Composition of exhaust from a ship diesel engine using heavy fuel oil (HFO) was investigated onbo... more Composition of exhaust from a ship diesel engine using heavy fuel oil (HFO) was investigated onboard a large cargo vessel. The emitted particulate matter (PM) properties related to environmental and health impacts were investigated along with composition of the gas-phase emissions. Mass, size distribution, chemical composition and microphysical structure of the PM were investigated. The emission factor for PM was 5.3 g (kg fuel) À1 . The mass size distribution showed a bimodal shape with two maxima: one in the accumulation mode with mean particle diameter D P around 0.5 mm and one in the coarse mode at D P around 7 mm. The PM composition was dominated by organic carbon (OC), ash and sulphate while the elemental carbon (EC) composed only a few percent of the total PM. Increase of the PM in exhaust upon cooling was associated with increase of OC and sulphate. Laser analysis of the adsorbed phase in the cooled exhaust showed presence of a rich mixture of polycyclic aromatic hydrocarbon (PAH) species with molecular mass 178-300 amu while PM collected in the hot exhaust showed only four PAH masses. Microstructure and elemental analysis of ship combustion residuals indicate three distinct morphological structures with different chemical composition: soot aggregates, significantly metal polluted; char particles, clean or containing minerals; mineral and/or ash particles. Additionally, organic carbon particles of unburned fuel or/and lubricating oil origin were observed. Hazardous constituents from the combustion of heavy fuel oil such as transitional and alkali earth metals (V, Ni, Ca, Fe) were observed in the PM samples. Measurements of gaseous composition in the exhaust of this particular ship showed emission factors that are on the low side of the interval of global emission factors published in literature for NO x , hydrocarbons (HC) and CO.
Considering that the motions of the particles take place on continuous but non-differentiable cur... more Considering that the motions of the particles take place on continuous but non-differentiable curves, i.e. on fractals with constant fractal dimension, an extended scale relativity model in its hydrodynamic version is built. In this approach, static (particle in a box and harmonic oscillator) and time-dependent (free particle etc.) systems are analyzed. The static systems can be associated with a coherent fractal fluid (of superconductor or of super-fluid types behavior), whose particles are moving on stationary trajectories. The complex speed field of the fractal fluid proves to be essential: the zero value of the real (differentiable) part specifies the coherence of the fractal fluid, while the non-zero value of the imaginary (non-differentiable or fractal) part selects, through some “quantization” relations, the “stationary” trajectories (that may correspond to the observables from quantum mechanics) of the fractal fluid particles. Moreover, the momentum transfer in the fractal fluid is achieved only through the fractal component of the complex speed field. The free time-dependent systems can be associated with an incoherent fractal fluid, and both the differentiable and fractal components of complex speed field are inhomogeneous in fractal coordinates due to the action of a fractal potential. It exist momentum transfer on both speed components and the “observable” in the form of an uniform motion is generated through a specific mechanism of “vacuum” polarization induced by the same fractal potential. The analysis on the fractal fluid specifies conductive properties in the case of movements synchronization both on differentiable and fractal scales, and convective properties in the absence of synchronization.
Thin films of formaldehyde-water mixtures are co-deposited at 88 K and 10 À1 Torr from gas collec... more Thin films of formaldehyde-water mixtures are co-deposited at 88 K and 10 À1 Torr from gas collected above formaldehyde aqueous solutions of different concentrations (5, 10, 15, 20, 30 mol%). They are analyzed in situ by micro-Raman scattering in the 2700-3800 cm À1 spectral range. The spectral characteristic of H 2 CO distributed molecularly in amorphous solid water is obtained under vacuum conditions. As temperature is increased formaldehyde is released during the crystallization of ice between 118 and 138 K. On the other hand, under controlled nitrogen atmosphere, the deposits crystallize in hydrate phases (or solid H 2 CO(s)) during annealing. A new phase (metastable FOR-A) of H 2 CO(s) (or a low hydrate after rejection by crystallizing ice) can be spectroscopically identified at 138 K before transformation into a hydrate (with molecular H 2 CO distributed within the cages of the clathrate FOR-B) takes place at 148 K. This latter phase decomposes between ca. 180 and 200 K. The significant spectral differences between these hydrates and those formed in frozen formaldehyde aqueous solutions reflect the existence of H 2 CO-clusters of distinctive structural nature relative to those resulting from important oligomerization process in the liquid. Moreover, the structure, the gas distribution and relative gas population in the formaldehyde clathrate cages are influenced by the relative amount of trapped nitrogen at the surface, which moreover depends on the ice film morphology. The dependence on the crystallization temperature of the deposits is explained by the relative amounts of occluded H 2 CO/N 2 and the external pressure conditions. The distinct behavior observed between vacuum and N 2 -atmosphere conditions certainly reflects a complex mechanism of surface mediated nucleation in which the transport of the reactants to the hydrate reaction zone is facilitated by the presence of a polar dopant.
Natural gas hydrates recovered from the Congo-Angola basin and Nigerian margins are analyzed by s... more Natural gas hydrates recovered from the Congo-Angola basin and Nigerian margins are analyzed by synchrotron X-ray powder diffraction. Biogenic methane is the most abundant gas trapped in the samples and others minor components (CO 2 , H 2 S) are co-clathrated in a type I cubic lattice structure. The refinement for the type I structure gives lattice parameters of a = 11.8646 (39) Å and a = 11.8619 (23) Å for specimens from Congo-Angola and Nigerian margins respectively at 90 K. These values, intermediate between the lattice constant of less pure methane specimens and pure artificial methane hydrates, indicate that lattice constants can be affected by the presence of encaged CO 2 , H 2 S and other gas molecules, even in small amounts. Thermal expansion is also presented for Congo-Angola hydrate in the temperature range 90-200 K. The coefficients are comparable with values reported for synthetic hydrates at low temperature and tend to approach thermal expansion of ice at higher temperature.
A new model of the atom is built based on a complete and detailed nonlinear dynamics analysis (co... more A new model of the atom is built based on a complete and detailed nonlinear dynamics analysis (complete time series, Poincaré sections, complete phase space, Lyapunov exponents, bifurcation diagrams and fractal analysis), through the correlation of the chaotic-stochastic model with a fractal one. Some specific mechanisms that ensure the atom functionality are proposed: gun, chaotic gun and multi-gun effects for the excited states (the classical analogue of quantum absorption) and the fractalization of the trajectories for the stationary states (a natural way of introducing the quantification).
The dynamics of a transient laser ablation plasma plume has been investigated by means of space- ... more The dynamics of a transient laser ablation plasma plume has been investigated by means of space- and time-resolved optical emission spectroscopy (OES), through a high-resolution monochromator and a fast gate ICCD camera. The experiments have been carried out with the third harmonic (355 nm) of a Q-switched (10 ns) Nd:YAG laser focused on Al2O3 samples placed in a vacuum chamber (10−7 Torr). The splitting of the plasma plume into two components has been evidenced by ICCD imaging. In the OES study, Al and O neutral atoms and different charge state ions have been monitored through the evolution of selected spectral lines. The two plume components (fast and slow) are found to consist mainly of charged and neutral species, respectively. Fundamental parameters of these species (e.g. excitation temperature) have been derived.
A new method is proposed to measure the ratio of the refractive index function of soot particles ... more A new method is proposed to measure the ratio of the refractive index function of soot particles E(m) at the two fixed wavelengths: 532 and 1064 nm. Using a non-intrusive, in-situ laser based technique, the ratio E(m,1064 nm)/E(m,532 nm) can be determined by comparing laser induced incandescence (LII) intensities at 532 and 1064 nm excitation wavelengths. The method consists of selecting laser energies that insure the equality of the LII signals in the low fluence regime under given conditions. Such equality is consistent with the fact that the soot particle will have reached the same temperature independently of the laser wavelength, i.e. the soot particle has absorbed the same energy. As the absorbed energy is proportional to the laser irradiance times E(m), the measurement of the laser energies required to insure perfect concordance of the LII intensities (spatially and temporally) serves to deduce the ratio E(m,1064 nm)/E(m,532 nm). The method is demonstrated in an acetylene/air flame, validated against extinction measurements performed by cavity ring-down spectroscopy (CRDS) by using laser radiations at 532 nm and 1064 nm and finally applied to different flame conditions.
Solid deposits have been formed at 88 K and 10 À1 Torr from ethanol-water gas collected above aqu... more Solid deposits have been formed at 88 K and 10 À1 Torr from ethanol-water gas collected above aqueous solutions of ethanol (EtOH) (0.6, 2, 4.5, 9 and 17 mol%). The composition of different gas mixtures varying between 1:16 and 1:0.8 EtOH:H 2 O are determined at 295 K using our experimental vapor-liquid equilibrium (VLE) data in combination with the Wilson model . The Wilson constants derived at this temperature are L 12 = 0.37(4) and L 21 = 0.58(5). The concentration of EtOH in the ice mixture can be calculated using these data and a kinetic model of condensation. It is found to vary between 9 and 65 mol% EtOH. The ice mixtures are analyzed in situ in a modified cryostage by micro-Raman spectroscopy. The distinct vibrational signatures of pure EtOH, EtOH aqueous solutions and EtOH-ice mixtures are identified in the 400-3800 cm À1 spectral range. Internal vibrational motions of EtOH molecules are affected by temperature and concentration. The presence of amorphous EtOH-ice phases at 88 K is demonstrated by the characteristic vibrational signatures of the n OH stretching modes. The crystallization of an EtOH hydrate is proposed during annealing at $140 K of a 65 mol% EtOH-ice mixture. According to our preliminary X-ray diffraction work, this phase has apparently a distinct structure from that of solid EtOH or from EtOH-clathtrate structures usually found in frozen aqueous solutions. For ice mixtures of lower EtOH content, a distinct hydrate phase crystallizes at $170 K. These results suggest that ice mixtures obtained by vapor deposition reflect the existence of EtOH clusters of a distinctive structural nature with respect to those encountered in frozen aqueous mixtures. #
We present the use of a combined laser desorption/multi-photon ionization/time-of-flight mass spe... more We present the use of a combined laser desorption/multi-photon ionization/time-of-flight mass spectrometry technique for the analysis of polycyclic aromatic hydrocarbon (PAH) solid samples. A thorough characterization of the first step (laser desorption) of this experimental technique has been performed. By varying the energy of the laser pulse, a specific response of each PAH has been evidenced for pure and mixed PAH sample desorption. This behaviour has also been studied with respect to the fragmentation processes. Similar studies on PAHs adsorbed on graphite evidenced the possibility of desorbing molecules from the adsorbed phase only, i.e. without a contribution from the graphite substrate. These findings represent important preliminary steps towards the final goal of setting up a completely characterized analytical method for the investigation of the adsorbed phase of soot particles generated in combustion processes.
Quantitative measurements of the partial vapor pressure of formaldehyde are performed above aqueo... more Quantitative measurements of the partial vapor pressure of formaldehyde are performed above aqueous H 2 CO solutions of different concentrations (from 10 -5 to 0.3 molar fraction) using mass spectrometry and IR diode laser spectroscopy. Both experimental techniques allow direct probing of the gas phase concentration collected at equilibrium above the aqueous solutions. A correlation is observed between the polymerization processes occurring in the solution and the partial pressure of H 2 CO measured at vapor liquid equilibrium (VLE). A similar correlation is observed from total pressure measurements for which the equilibrium vapor pressure decreases as [ H 2 CO VLE ] liq is increased. A saturation regime of the H 2 CO partial pressure is reached as the dissolved fraction of formaldehyde increases above ∼0.15 mol frac. Henry's law constants are derived at 295K for the diluted solutions.
Species adsorbed at the surfaces of soot particles sampled at different locations in a low-pressu... more Species adsorbed at the surfaces of soot particles sampled at different locations in a low-pressure methane flame have been analyzed. The analysis method is laser desorption/laser ionization/time-of-flight mass spectrometry (LD/LI/TOF-MS) applied to soot particles deposited on a filter after probe extraction in the flame. In order to fully characterize the experimental apparatus, a strategy of systematic investigations has been adopted, beginning with the study of less complex systems constituted by model soot (standard polycyclic aromatic hydrocarbons, PAHs, adsorbed on black carbon), and then natural soot sampled from a literature reference ethylene flame. This characterization allowed a good understanding of the analytical response of PAHs to the desorption and ionization processes and the definition of the optimal experimental conditions. The soot PAH content was then investigated on a low-pressure methane/oxygen/nitrogen premixed flat flame (/ = 2.32) as a function of the sampling height above the burner (HAB). The obtained mass spectra are reproducible, fragment-free, well resolved in the analyzed m/z range and they are characterized by an excellent signal-to-noise ratio. They all feature regular peak sequences, where each signal peak has been assigned to the most stable high-temperature-formed PAHs. The structure of the mass spectra depends on the sampling HAB into the flame, i.e., on the reaction time. An original contribution to the data interpretation comes from the development of a new sampling method that makes it possible to infer hypotheses about the PAH partition between the gas phase and the soot particles. This method highlights the presence of high-mass PAHs in the soot nucleation zone, and it suggests the importance of heterogeneous reactions occurring between flame PAHs and soot particles.
The formation and dynamics of aluminum laser produced plasma are experimentally and theoretically... more The formation and dynamics of aluminum laser produced plasma are experimentally and theoretically investigated. The visible emitting regions of plasma form two structures of different expansion velocities. Such behavior is in agreement with the transient current recorded by a cylindrical Langmuir probe. Using the hydrodynamic model of scale relativity theory, the plasma dynamics at different time scales are numerically and analytically analyzed. #
Long series of hydrated clusters of organic molecules (formaldehyde, methanol, ethanol and trypto... more Long series of hydrated clusters of organic molecules (formaldehyde, methanol, ethanol and tryptophan) have been generated by infrared optical parametric oscillator (OPO) resonant desorption of frozen aqueous solutions. Using a comparative approach, we derived some general trends from cluster size and velocity distribution measurements. In the biologically interesting case of tryptophan amino acid, our technique yields a much longer (and complete) series of hydrated clusters than that obtained previously using a combined laser desorption/pulsed jet expansion technique [L.C. Snoek, R.T. Kroemer, J.P. Simons: Phys. Chem. Chem. Phys. 4, 2130 (2002)].
Soot formation is compared in turbulent diffusion flames burning a commercial Diesel and two Dies... more Soot formation is compared in turbulent diffusion flames burning a commercial Diesel and two Diesel surrogates containing n-decane and a-methylnaphthalene. A burner equipped with a high-efficiency atomisation system has been specially designed and allows the stabilisation of liquid fuels flames with similar hydrodynamics conditions. The initial surrogate composition (70% n-decane, 30% a-methylnaphthalene) was previously used in the literature to simulate combustion in Diesel engines. In this work, a direct comparison of Diesel and surrogates soot tendencies is undertaken and relies on soot and fluorescent species mappings obtained respectively by Laser-Induced Incandescence (LII) at 1064 nm and Laser-Induced Fluorescence at 532 nm. LIF was assigned to soot precursors and mainly to high-number ring Polycyclic Aromatic Hydrocarbons (PAH). The initial surrogate was found to form 40% more soot than the tested Diesel. Consequently, a second surrogate containing a lower a-methylnaphthalene concentration (20%) has been formulated. That composition which presents a Threshold Soot Index (TSI) very close to Diesel one is also consistent with our Diesel composition that indicates a relatively low PAH content. The spatially resolved measurements of soot and fluorescent soot precursors are quite identical (in shape and intensity) in the Diesel and in the second surrogate flames. Furthermore the concordance of the LII temporal decays suggests that a similar growth of the primary soot particles has occurred for Diesel and surrogates. In addition, the comparison of the LII fluence curves indicates that physical/optical properties of soot contained in the different flames might be similar. The chemical composition present at the surface of soot particles collected in Diesel and surrogate flames has been obtained by laser-desorption ionisation time-offlight mass spectrometry. An important difference is found between Diesel and surrogate samples indicating the influence of the fuel composition on soot content.
We investigate the resonant character of the laser desorption of polycyclic aromatic hydrocarbons... more We investigate the resonant character of the laser desorption of polycyclic aromatic hydrocarbons (PAH) in the 3.3 lm range by exciting the C-H stretching with a tunable pulsed LiNbO 3 optical parametric oscillator. A perfect match is obtained between the desorption yield and the optical absorption spectra of naphthalene, acenaphtene, and phenanthrene. The plume dynamics is probed by varying the delay between the desorption and ionization laser pulses. Simple calculations using Beer-Lambert and Hertz-Knudsen equations account for the absence of phase explosion mechanism and for the long desorption times observed. Analytical and technological openings of this resonant technique are discussed.
The formation and dynamics of a laser-produced aluminum plasma have been experimentally and theor... more The formation and dynamics of a laser-produced aluminum plasma have been experimentally and theoretically investigated. The visible-emitting regions of the plasma form two structures with different lifetimes and expansion velocities. The first part of the transient ionic signal simultaneously recorded by a Langmuir probe presents an oscillatory structure. A hydrodynamic model in a nondifferentiable space-time has been established. The numerical simulation of the plasma expansion showed the plasma plume separation into two patterns. Moreover, the self-structuring of the interface appears through a negative differential conductance and the current oscillations are explained as being induced by thermal fluctuations that appear in the plasma cooling processes.
Recent advances in the field of laser desorption/laser ionization mass spectrometry (LD/LI/MS) ha... more Recent advances in the field of laser desorption/laser ionization mass spectrometry (LD/LI/MS) have renewed interest in these separation methods for fast analysis of chemical species adsorbed on soot particles. These techniques provide mass-separation of the desorbed phase with high selectivity and sensitivity and require very small soot samples. Combining LD/LI/MS with in situ measurements of soot and gaseous species is very promising for a better understanding of the early stage of soot growth in flames. In this work, three lightly sooting laminar jet flames (a methane diffusion flame and two premixed acetylene flames of equivalence ratio (/) = 2.9 and 3.5) were investigated by combining prompt and 50 ns-delayed laser-induced incandescence (LII) for spatially resolved measurements of soot volume fraction (f v ) and laser-induced fluorescence (LIF) of polycyclic aromatic hydrocarbons (PAH). Soot and PAH calibration is performed by two-colour cavity ring-down spectroscopy (CRDS) at 1064 and 532 nm. Soot particles were sampled in the flames and analysed by LD/LI/Time-of-flight-MS. Soot samples are cooled to À170°C to avoid adsorbed phase sublimation (under high vacuum in the TOF-MS). Our set-up is novel because of its ability to measure very low concentration of soot and PAH together with the ability to identify a large mass range of PAHs adsorbed on soot, especially volatile two-rings and three-rings PAHs. Studied flames exhibited a peak f v ranging from 15 ppb (acetylene, / = 2.9) to 470 ppb (acetylene, / = 3.5). Different mass spectra were found in the three flames, each exhibiting one predominant PAH mass; 202 amu (4-rings) in methane, 178 amu (3-rings) in acetylene,/ = 2.9 and 128 amu (2-rings) in acetylene, / = 3.5. These variations with flame condition contrasts with other recent studies and is discussed. The other PAH masses ranged from 102 (C 8 H 6 ) to 424 amu (C 34 H 16 ) and are well predicted by the stabilomer grid of Stein and Farr.
Rapidly frozen aqueous solutions containing variable amounts of dissolved formaldehyde (0.1, 5, 7... more Rapidly frozen aqueous solutions containing variable amounts of dissolved formaldehyde (0.1, 5, 7, 10, 15, and 20 mol %) have been analyzed by micro-Raman spectroscopy at ambient pressure and low temperature. The importance of the formladehyde-ice system has been repeatedly quoted in various contexts, such as atmospheric and snowpack chemistry and interstellar and cometary ices. Understanding and characterizing the effects of freezing and the interactions of formaldehyde with ice are therefore of relevant interest. In this study, the distinct vibrational signatures of the oligomers present in the solution and in the frozen ice mixtures have been identified in the 120-4000 cm -1 spectral range. From the subtle changes of the bands assigned to the CO and CH group frequencies, at least two distinct crystalline phases (pI and pII) are found to coexist with ice at different temperatures. Depending on the cooling-rewarming protocol, pI is found to crystallize in the 163-213 K temperature range. Above ∼213 K, pI gets transformed irreversibly into pII which is stable up to ∼234 K. pII is found to interact more strongly with ice than pI, as revealed, for example, by the drop in frequency of the bands assigned to the O-H stretching as pI transforms into pII. It is suggested that pII consists of a hydrogen-bonded network of oligomers and water molecules. On the other hand, it is suggested that the oligomers mainly present in pI interact through weak forces with the surrounding water molecules.
The microscopic structures of neat liquid nicotine and nicotine-water mixtures are examined throu... more The microscopic structures of neat liquid nicotine and nicotine-water mixtures are examined through infrared spectroscopy and laser resonant desorption mass-spectroscopy. The infrared spectra of the solutions are analyzed using DFT calculations of homogenous and mixed hydrogen-bonded clusters. Neat nicotine and hydrated nicotine cluster are experimentally observed through IR laser resonant desorption of a nicotine/water ice mixture followed by laser ionization mass-spectrometry. A sizable fraction of those cluster ions is the result of laser ionization of small neutral clusters already present in the sample.
Composition of exhaust from a ship diesel engine using heavy fuel oil (HFO) was investigated onbo... more Composition of exhaust from a ship diesel engine using heavy fuel oil (HFO) was investigated onboard a large cargo vessel. The emitted particulate matter (PM) properties related to environmental and health impacts were investigated along with composition of the gas-phase emissions. Mass, size distribution, chemical composition and microphysical structure of the PM were investigated. The emission factor for PM was 5.3 g (kg fuel) À1 . The mass size distribution showed a bimodal shape with two maxima: one in the accumulation mode with mean particle diameter D P around 0.5 mm and one in the coarse mode at D P around 7 mm. The PM composition was dominated by organic carbon (OC), ash and sulphate while the elemental carbon (EC) composed only a few percent of the total PM. Increase of the PM in exhaust upon cooling was associated with increase of OC and sulphate. Laser analysis of the adsorbed phase in the cooled exhaust showed presence of a rich mixture of polycyclic aromatic hydrocarbon (PAH) species with molecular mass 178-300 amu while PM collected in the hot exhaust showed only four PAH masses. Microstructure and elemental analysis of ship combustion residuals indicate three distinct morphological structures with different chemical composition: soot aggregates, significantly metal polluted; char particles, clean or containing minerals; mineral and/or ash particles. Additionally, organic carbon particles of unburned fuel or/and lubricating oil origin were observed. Hazardous constituents from the combustion of heavy fuel oil such as transitional and alkali earth metals (V, Ni, Ca, Fe) were observed in the PM samples. Measurements of gaseous composition in the exhaust of this particular ship showed emission factors that are on the low side of the interval of global emission factors published in literature for NO x , hydrocarbons (HC) and CO.
Considering that the motions of the particles take place on continuous but non-differentiable cur... more Considering that the motions of the particles take place on continuous but non-differentiable curves, i.e. on fractals with constant fractal dimension, an extended scale relativity model in its hydrodynamic version is built. In this approach, static (particle in a box and harmonic oscillator) and time-dependent (free particle etc.) systems are analyzed. The static systems can be associated with a coherent fractal fluid (of superconductor or of super-fluid types behavior), whose particles are moving on stationary trajectories. The complex speed field of the fractal fluid proves to be essential: the zero value of the real (differentiable) part specifies the coherence of the fractal fluid, while the non-zero value of the imaginary (non-differentiable or fractal) part selects, through some “quantization” relations, the “stationary” trajectories (that may correspond to the observables from quantum mechanics) of the fractal fluid particles. Moreover, the momentum transfer in the fractal fluid is achieved only through the fractal component of the complex speed field. The free time-dependent systems can be associated with an incoherent fractal fluid, and both the differentiable and fractal components of complex speed field are inhomogeneous in fractal coordinates due to the action of a fractal potential. It exist momentum transfer on both speed components and the “observable” in the form of an uniform motion is generated through a specific mechanism of “vacuum” polarization induced by the same fractal potential. The analysis on the fractal fluid specifies conductive properties in the case of movements synchronization both on differentiable and fractal scales, and convective properties in the absence of synchronization.
Thin films of formaldehyde-water mixtures are co-deposited at 88 K and 10 À1 Torr from gas collec... more Thin films of formaldehyde-water mixtures are co-deposited at 88 K and 10 À1 Torr from gas collected above formaldehyde aqueous solutions of different concentrations (5, 10, 15, 20, 30 mol%). They are analyzed in situ by micro-Raman scattering in the 2700-3800 cm À1 spectral range. The spectral characteristic of H 2 CO distributed molecularly in amorphous solid water is obtained under vacuum conditions. As temperature is increased formaldehyde is released during the crystallization of ice between 118 and 138 K. On the other hand, under controlled nitrogen atmosphere, the deposits crystallize in hydrate phases (or solid H 2 CO(s)) during annealing. A new phase (metastable FOR-A) of H 2 CO(s) (or a low hydrate after rejection by crystallizing ice) can be spectroscopically identified at 138 K before transformation into a hydrate (with molecular H 2 CO distributed within the cages of the clathrate FOR-B) takes place at 148 K. This latter phase decomposes between ca. 180 and 200 K. The significant spectral differences between these hydrates and those formed in frozen formaldehyde aqueous solutions reflect the existence of H 2 CO-clusters of distinctive structural nature relative to those resulting from important oligomerization process in the liquid. Moreover, the structure, the gas distribution and relative gas population in the formaldehyde clathrate cages are influenced by the relative amount of trapped nitrogen at the surface, which moreover depends on the ice film morphology. The dependence on the crystallization temperature of the deposits is explained by the relative amounts of occluded H 2 CO/N 2 and the external pressure conditions. The distinct behavior observed between vacuum and N 2 -atmosphere conditions certainly reflects a complex mechanism of surface mediated nucleation in which the transport of the reactants to the hydrate reaction zone is facilitated by the presence of a polar dopant.
Natural gas hydrates recovered from the Congo-Angola basin and Nigerian margins are analyzed by s... more Natural gas hydrates recovered from the Congo-Angola basin and Nigerian margins are analyzed by synchrotron X-ray powder diffraction. Biogenic methane is the most abundant gas trapped in the samples and others minor components (CO 2 , H 2 S) are co-clathrated in a type I cubic lattice structure. The refinement for the type I structure gives lattice parameters of a = 11.8646 (39) Å and a = 11.8619 (23) Å for specimens from Congo-Angola and Nigerian margins respectively at 90 K. These values, intermediate between the lattice constant of less pure methane specimens and pure artificial methane hydrates, indicate that lattice constants can be affected by the presence of encaged CO 2 , H 2 S and other gas molecules, even in small amounts. Thermal expansion is also presented for Congo-Angola hydrate in the temperature range 90-200 K. The coefficients are comparable with values reported for synthetic hydrates at low temperature and tend to approach thermal expansion of ice at higher temperature.
A new model of the atom is built based on a complete and detailed nonlinear dynamics analysis (co... more A new model of the atom is built based on a complete and detailed nonlinear dynamics analysis (complete time series, Poincaré sections, complete phase space, Lyapunov exponents, bifurcation diagrams and fractal analysis), through the correlation of the chaotic-stochastic model with a fractal one. Some specific mechanisms that ensure the atom functionality are proposed: gun, chaotic gun and multi-gun effects for the excited states (the classical analogue of quantum absorption) and the fractalization of the trajectories for the stationary states (a natural way of introducing the quantification).
The dynamics of a transient laser ablation plasma plume has been investigated by means of space- ... more The dynamics of a transient laser ablation plasma plume has been investigated by means of space- and time-resolved optical emission spectroscopy (OES), through a high-resolution monochromator and a fast gate ICCD camera. The experiments have been carried out with the third harmonic (355 nm) of a Q-switched (10 ns) Nd:YAG laser focused on Al2O3 samples placed in a vacuum chamber (10−7 Torr). The splitting of the plasma plume into two components has been evidenced by ICCD imaging. In the OES study, Al and O neutral atoms and different charge state ions have been monitored through the evolution of selected spectral lines. The two plume components (fast and slow) are found to consist mainly of charged and neutral species, respectively. Fundamental parameters of these species (e.g. excitation temperature) have been derived.
A new method is proposed to measure the ratio of the refractive index function of soot particles ... more A new method is proposed to measure the ratio of the refractive index function of soot particles E(m) at the two fixed wavelengths: 532 and 1064 nm. Using a non-intrusive, in-situ laser based technique, the ratio E(m,1064 nm)/E(m,532 nm) can be determined by comparing laser induced incandescence (LII) intensities at 532 and 1064 nm excitation wavelengths. The method consists of selecting laser energies that insure the equality of the LII signals in the low fluence regime under given conditions. Such equality is consistent with the fact that the soot particle will have reached the same temperature independently of the laser wavelength, i.e. the soot particle has absorbed the same energy. As the absorbed energy is proportional to the laser irradiance times E(m), the measurement of the laser energies required to insure perfect concordance of the LII intensities (spatially and temporally) serves to deduce the ratio E(m,1064 nm)/E(m,532 nm). The method is demonstrated in an acetylene/air flame, validated against extinction measurements performed by cavity ring-down spectroscopy (CRDS) by using laser radiations at 532 nm and 1064 nm and finally applied to different flame conditions.
Solid deposits have been formed at 88 K and 10 À1 Torr from ethanol-water gas collected above aqu... more Solid deposits have been formed at 88 K and 10 À1 Torr from ethanol-water gas collected above aqueous solutions of ethanol (EtOH) (0.6, 2, 4.5, 9 and 17 mol%). The composition of different gas mixtures varying between 1:16 and 1:0.8 EtOH:H 2 O are determined at 295 K using our experimental vapor-liquid equilibrium (VLE) data in combination with the Wilson model . The Wilson constants derived at this temperature are L 12 = 0.37(4) and L 21 = 0.58(5). The concentration of EtOH in the ice mixture can be calculated using these data and a kinetic model of condensation. It is found to vary between 9 and 65 mol% EtOH. The ice mixtures are analyzed in situ in a modified cryostage by micro-Raman spectroscopy. The distinct vibrational signatures of pure EtOH, EtOH aqueous solutions and EtOH-ice mixtures are identified in the 400-3800 cm À1 spectral range. Internal vibrational motions of EtOH molecules are affected by temperature and concentration. The presence of amorphous EtOH-ice phases at 88 K is demonstrated by the characteristic vibrational signatures of the n OH stretching modes. The crystallization of an EtOH hydrate is proposed during annealing at $140 K of a 65 mol% EtOH-ice mixture. According to our preliminary X-ray diffraction work, this phase has apparently a distinct structure from that of solid EtOH or from EtOH-clathtrate structures usually found in frozen aqueous solutions. For ice mixtures of lower EtOH content, a distinct hydrate phase crystallizes at $170 K. These results suggest that ice mixtures obtained by vapor deposition reflect the existence of EtOH clusters of a distinctive structural nature with respect to those encountered in frozen aqueous mixtures. #
We present the use of a combined laser desorption/multi-photon ionization/time-of-flight mass spe... more We present the use of a combined laser desorption/multi-photon ionization/time-of-flight mass spectrometry technique for the analysis of polycyclic aromatic hydrocarbon (PAH) solid samples. A thorough characterization of the first step (laser desorption) of this experimental technique has been performed. By varying the energy of the laser pulse, a specific response of each PAH has been evidenced for pure and mixed PAH sample desorption. This behaviour has also been studied with respect to the fragmentation processes. Similar studies on PAHs adsorbed on graphite evidenced the possibility of desorbing molecules from the adsorbed phase only, i.e. without a contribution from the graphite substrate. These findings represent important preliminary steps towards the final goal of setting up a completely characterized analytical method for the investigation of the adsorbed phase of soot particles generated in combustion processes.
Quantitative measurements of the partial vapor pressure of formaldehyde are performed above aqueo... more Quantitative measurements of the partial vapor pressure of formaldehyde are performed above aqueous H 2 CO solutions of different concentrations (from 10 -5 to 0.3 molar fraction) using mass spectrometry and IR diode laser spectroscopy. Both experimental techniques allow direct probing of the gas phase concentration collected at equilibrium above the aqueous solutions. A correlation is observed between the polymerization processes occurring in the solution and the partial pressure of H 2 CO measured at vapor liquid equilibrium (VLE). A similar correlation is observed from total pressure measurements for which the equilibrium vapor pressure decreases as [ H 2 CO VLE ] liq is increased. A saturation regime of the H 2 CO partial pressure is reached as the dissolved fraction of formaldehyde increases above ∼0.15 mol frac. Henry's law constants are derived at 295K for the diluted solutions.
Species adsorbed at the surfaces of soot particles sampled at different locations in a low-pressu... more Species adsorbed at the surfaces of soot particles sampled at different locations in a low-pressure methane flame have been analyzed. The analysis method is laser desorption/laser ionization/time-of-flight mass spectrometry (LD/LI/TOF-MS) applied to soot particles deposited on a filter after probe extraction in the flame. In order to fully characterize the experimental apparatus, a strategy of systematic investigations has been adopted, beginning with the study of less complex systems constituted by model soot (standard polycyclic aromatic hydrocarbons, PAHs, adsorbed on black carbon), and then natural soot sampled from a literature reference ethylene flame. This characterization allowed a good understanding of the analytical response of PAHs to the desorption and ionization processes and the definition of the optimal experimental conditions. The soot PAH content was then investigated on a low-pressure methane/oxygen/nitrogen premixed flat flame (/ = 2.32) as a function of the sampling height above the burner (HAB). The obtained mass spectra are reproducible, fragment-free, well resolved in the analyzed m/z range and they are characterized by an excellent signal-to-noise ratio. They all feature regular peak sequences, where each signal peak has been assigned to the most stable high-temperature-formed PAHs. The structure of the mass spectra depends on the sampling HAB into the flame, i.e., on the reaction time. An original contribution to the data interpretation comes from the development of a new sampling method that makes it possible to infer hypotheses about the PAH partition between the gas phase and the soot particles. This method highlights the presence of high-mass PAHs in the soot nucleation zone, and it suggests the importance of heterogeneous reactions occurring between flame PAHs and soot particles.
The formation and dynamics of aluminum laser produced plasma are experimentally and theoretically... more The formation and dynamics of aluminum laser produced plasma are experimentally and theoretically investigated. The visible emitting regions of plasma form two structures of different expansion velocities. Such behavior is in agreement with the transient current recorded by a cylindrical Langmuir probe. Using the hydrodynamic model of scale relativity theory, the plasma dynamics at different time scales are numerically and analytically analyzed. #
Long series of hydrated clusters of organic molecules (formaldehyde, methanol, ethanol and trypto... more Long series of hydrated clusters of organic molecules (formaldehyde, methanol, ethanol and tryptophan) have been generated by infrared optical parametric oscillator (OPO) resonant desorption of frozen aqueous solutions. Using a comparative approach, we derived some general trends from cluster size and velocity distribution measurements. In the biologically interesting case of tryptophan amino acid, our technique yields a much longer (and complete) series of hydrated clusters than that obtained previously using a combined laser desorption/pulsed jet expansion technique [L.C. Snoek, R.T. Kroemer, J.P. Simons: Phys. Chem. Chem. Phys. 4, 2130 (2002)].
Soot formation is compared in turbulent diffusion flames burning a commercial Diesel and two Dies... more Soot formation is compared in turbulent diffusion flames burning a commercial Diesel and two Diesel surrogates containing n-decane and a-methylnaphthalene. A burner equipped with a high-efficiency atomisation system has been specially designed and allows the stabilisation of liquid fuels flames with similar hydrodynamics conditions. The initial surrogate composition (70% n-decane, 30% a-methylnaphthalene) was previously used in the literature to simulate combustion in Diesel engines. In this work, a direct comparison of Diesel and surrogates soot tendencies is undertaken and relies on soot and fluorescent species mappings obtained respectively by Laser-Induced Incandescence (LII) at 1064 nm and Laser-Induced Fluorescence at 532 nm. LIF was assigned to soot precursors and mainly to high-number ring Polycyclic Aromatic Hydrocarbons (PAH). The initial surrogate was found to form 40% more soot than the tested Diesel. Consequently, a second surrogate containing a lower a-methylnaphthalene concentration (20%) has been formulated. That composition which presents a Threshold Soot Index (TSI) very close to Diesel one is also consistent with our Diesel composition that indicates a relatively low PAH content. The spatially resolved measurements of soot and fluorescent soot precursors are quite identical (in shape and intensity) in the Diesel and in the second surrogate flames. Furthermore the concordance of the LII temporal decays suggests that a similar growth of the primary soot particles has occurred for Diesel and surrogates. In addition, the comparison of the LII fluence curves indicates that physical/optical properties of soot contained in the different flames might be similar. The chemical composition present at the surface of soot particles collected in Diesel and surrogate flames has been obtained by laser-desorption ionisation time-offlight mass spectrometry. An important difference is found between Diesel and surrogate samples indicating the influence of the fuel composition on soot content.
We investigate the resonant character of the laser desorption of polycyclic aromatic hydrocarbons... more We investigate the resonant character of the laser desorption of polycyclic aromatic hydrocarbons (PAH) in the 3.3 lm range by exciting the C-H stretching with a tunable pulsed LiNbO 3 optical parametric oscillator. A perfect match is obtained between the desorption yield and the optical absorption spectra of naphthalene, acenaphtene, and phenanthrene. The plume dynamics is probed by varying the delay between the desorption and ionization laser pulses. Simple calculations using Beer-Lambert and Hertz-Knudsen equations account for the absence of phase explosion mechanism and for the long desorption times observed. Analytical and technological openings of this resonant technique are discussed.
The formation and dynamics of a laser-produced aluminum plasma have been experimentally and theor... more The formation and dynamics of a laser-produced aluminum plasma have been experimentally and theoretically investigated. The visible-emitting regions of the plasma form two structures with different lifetimes and expansion velocities. The first part of the transient ionic signal simultaneously recorded by a Langmuir probe presents an oscillatory structure. A hydrodynamic model in a nondifferentiable space-time has been established. The numerical simulation of the plasma expansion showed the plasma plume separation into two patterns. Moreover, the self-structuring of the interface appears through a negative differential conductance and the current oscillations are explained as being induced by thermal fluctuations that appear in the plasma cooling processes.
Recent advances in the field of laser desorption/laser ionization mass spectrometry (LD/LI/MS) ha... more Recent advances in the field of laser desorption/laser ionization mass spectrometry (LD/LI/MS) have renewed interest in these separation methods for fast analysis of chemical species adsorbed on soot particles. These techniques provide mass-separation of the desorbed phase with high selectivity and sensitivity and require very small soot samples. Combining LD/LI/MS with in situ measurements of soot and gaseous species is very promising for a better understanding of the early stage of soot growth in flames. In this work, three lightly sooting laminar jet flames (a methane diffusion flame and two premixed acetylene flames of equivalence ratio (/) = 2.9 and 3.5) were investigated by combining prompt and 50 ns-delayed laser-induced incandescence (LII) for spatially resolved measurements of soot volume fraction (f v ) and laser-induced fluorescence (LIF) of polycyclic aromatic hydrocarbons (PAH). Soot and PAH calibration is performed by two-colour cavity ring-down spectroscopy (CRDS) at 1064 and 532 nm. Soot particles were sampled in the flames and analysed by LD/LI/Time-of-flight-MS. Soot samples are cooled to À170°C to avoid adsorbed phase sublimation (under high vacuum in the TOF-MS). Our set-up is novel because of its ability to measure very low concentration of soot and PAH together with the ability to identify a large mass range of PAHs adsorbed on soot, especially volatile two-rings and three-rings PAHs. Studied flames exhibited a peak f v ranging from 15 ppb (acetylene, / = 2.9) to 470 ppb (acetylene, / = 3.5). Different mass spectra were found in the three flames, each exhibiting one predominant PAH mass; 202 amu (4-rings) in methane, 178 amu (3-rings) in acetylene,/ = 2.9 and 128 amu (2-rings) in acetylene, / = 3.5. These variations with flame condition contrasts with other recent studies and is discussed. The other PAH masses ranged from 102 (C 8 H 6 ) to 424 amu (C 34 H 16 ) and are well predicted by the stabilomer grid of Stein and Farr.
Rapidly frozen aqueous solutions containing variable amounts of dissolved formaldehyde (0.1, 5, 7... more Rapidly frozen aqueous solutions containing variable amounts of dissolved formaldehyde (0.1, 5, 7, 10, 15, and 20 mol %) have been analyzed by micro-Raman spectroscopy at ambient pressure and low temperature. The importance of the formladehyde-ice system has been repeatedly quoted in various contexts, such as atmospheric and snowpack chemistry and interstellar and cometary ices. Understanding and characterizing the effects of freezing and the interactions of formaldehyde with ice are therefore of relevant interest. In this study, the distinct vibrational signatures of the oligomers present in the solution and in the frozen ice mixtures have been identified in the 120-4000 cm -1 spectral range. From the subtle changes of the bands assigned to the CO and CH group frequencies, at least two distinct crystalline phases (pI and pII) are found to coexist with ice at different temperatures. Depending on the cooling-rewarming protocol, pI is found to crystallize in the 163-213 K temperature range. Above ∼213 K, pI gets transformed irreversibly into pII which is stable up to ∼234 K. pII is found to interact more strongly with ice than pI, as revealed, for example, by the drop in frequency of the bands assigned to the O-H stretching as pI transforms into pII. It is suggested that pII consists of a hydrogen-bonded network of oligomers and water molecules. On the other hand, it is suggested that the oligomers mainly present in pI interact through weak forces with the surrounding water molecules.
The microscopic structures of neat liquid nicotine and nicotine-water mixtures are examined throu... more The microscopic structures of neat liquid nicotine and nicotine-water mixtures are examined through infrared spectroscopy and laser resonant desorption mass-spectroscopy. The infrared spectra of the solutions are analyzed using DFT calculations of homogenous and mixed hydrogen-bonded clusters. Neat nicotine and hydrated nicotine cluster are experimentally observed through IR laser resonant desorption of a nicotine/water ice mixture followed by laser ionization mass-spectrometry. A sizable fraction of those cluster ions is the result of laser ionization of small neutral clusters already present in the sample.
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Papers by Cristian FOCSA