Electron Impact Ionization

The total cross-sections for the single electron-impact ionization of pyrimidine (C 4 H 4 N 2), 2-chloropyrimidine (2-C 4 H 3 ClN 2), 5-chloropyrimidine (5-C 4 H 3 ClN 2), 2bromopyrimidine (2-C 4 H 3 BrN 2) and 5-bromopyrimidine (5-C 4 H 3 BrN 2) molecules have been calculated with the binary-encounter-Bethe model from the ionization threshold up to 5 keV. The input data for the BEB calculations concerning electronic structure of the studied targets have been obtained with quantum chemical methods including the Hartree-Fock (H-F) and the outer valence Green function (OVGF) methods. The calculated cross-section for the ionization of the pyrimidine molecules due to electron impact is compared with available experimental and theoretical data. The question of the magnitude the pyrimidine ionization cross-section is also discussed, as is the efficiency of the ionization process of studied halogenated derivatives of pyrimidine.

Abstract. The resonant states of HeH are computed by combining structure calculations at a full configuration interaction level with electron scattering calculations carried out using the Complex-Kohn variational method. We obtain the potential energy curves, autoionization widths, as well as non-adiabatic couplings among the resonant states. Using the non-adiabatic couplings, the adiabatic to diabatic transformation matrix can be obtained. A strict diabatization of the resonant states will be used to study various scattering processes where the resonant states are involved. These processes involve high energy dissociative recombination (DR) and ion-pair formation (RIP), resonant and direct dissociative excitation (DE), penning ionization (PI) as well as mutual neutralization (MN). 1.

Multiphoton ionization mechanisms and ionization rates of atmospheric air and constituent gases are studied at the 248-nm KrF laser wavelength within a laser pulse intensity range of 108–1013 W/cm2 using both long 25-ns and short 160-fs pulses. We have experimentally shown that it is the photoionization of water vapor naturally contained in atmospheric air that acts as the dominant process of air ionization. (2 + 1) Resonance-Enhanced Multiphoton Ionization (REMPI) occurs through 2-photon resonant excitation of water molecules, which results in a quadratic dependence of electron density on laser intensity at lower laser intensities of 108–1010 W/cm2 in the long pulse and in a cubic dependence at higher intensities of 1010–1013 W/cm2 in the short pulse. Direct 3-photon ionization and (3 + 1) REMPI take place in pure O2 and N2, respectively, and their contributions to air ionization are in the ratio of 5:3. The total ionization rate of O2 and N2 in atmospheric air is about an order of...

Electron impact ionization has several known advantages; however, heated filament electron sources have pressure limitations and their power consumption can be significant for certain applications, such as in field-portable instruments. Herein, we evaluate a VUV krypton lamp as an alternative source for ionization inside the ion trap of a mass spectrometer. The observed fragmentation patterns are more characteristic of electron impact ionization than photoionization. In addition, mass spectra of analytes with ionization potentials higher than the lamp's photon energy (10.6 eV) can be easily obtained. A photoelectron impact ionization mechanism is suggested by the observed data allowed by the work function of the ion trap electrodes (4.5 eV), which is well within the lamp's photon energy. In this case, the photoelectrons emitted at the surface of the ion trap end-cap electrode are accelerated by the applied rf field to the ring electrode. This allows the photoelectrons to gain sufficient energy to ionize compounds with high ionization potentials to yield mass spectra characteristic of electron impact. In this manner, electron impact ionization can be used in ion trap mass spectrometers at low powers and without the limitations imposed by elevated pressures on heated filaments.

Atomic structure data, electron impact excitations and ionization cross sections of tungsten ions, W 44+ , have been calculated using the multi-configuration Dirac-Fock and R-matrix methods for a set of configurations consists of 3 d 10 4 s 2 , 3 d 10 4 s 4 l , and 3 d 10 4 p 4 l . A set of configuration state functions (CSFs) with doubly excitations up to 5 l orbitals have been included within the calculations of energy levels and transition probabilities. As well as, 4-electron excitation to 4 l -levels and 3-electron to 5 l -levels have been involved in the computation process. R-matrix calculations of collision strength and cross section have been executed for the intercombination transitions between 3d 10 4s 2 , 3d 10 4s4p, 3d 10 4s4d, and 3d 10 4s4f at different angular momenta using DARC code. Resonance collision strengths have been observed at low energy of incident electron in the range of ∼ 6 -40 Ryd, however, the strong lines are limited to 6-25 Ryd. For cross section of various transitions, resonances arising from these transitions are observed at low-electron energies in the range of 6-25 Ryd. To estimate the accuracies of calculated energy levels and transition probabilities, comparisons between experimental observations and theoretical calculations are presented. The convergence between different methods for collision strengths and cross sections are observed. Different calculations of electron impact ionization cross section of the present ion in the collision energy range of 100-1000 Ryd are evaluated.

Excitation cross sections by electron impact of tungsten ions, W 39+ , have been calculated using R-matrix method for a configuration state list consists of [Ar]3d 10 4s 2 4p 5 , [Ar]3d 10 4s 2 4p 4 4l, (l = d, f ), and [Ar]3d 10 4s 2 4p 4 5l , l = s, p. A set of configuration state functions (CSFs) with 2-electron excitations up to 5l orbitals have been included within the MCDF-calculations of the used radial integrals of collisional excitations. R-matrix calculations of collision strength and cross section have been executed for the intercombination transitions between 4p 5 , 4p 4 4d, and 4p 4 4f at different angular momenta using DARC code. Resonance cross section have been observed at low energy of incident electron in the range of ∼5-40 Ryd, however, the strong lines limited between 5-25 Ryd. The relativistic distorted-wave (DW) approximation, Coulomb-Born-Exchange (CBE) approximation, and the Binary-Encounter-Dipole (BED) theory have been used to calculate the electron impact ionization (EII) of the present ion. The accuracies of the present results are estimated by comparing R-matrix calculations with the available literature.

Maxwellian electron energy distributions in a highly non-equilibrium plasma of low pressure dc discharges is one the oldest and fascinating mysteries of gas discharge physics. There is extensive literature and many hypotheses attempting to explain this paradox, but the ...

Heacl space gas chromatography with flame-ionization detection (HS-GC-FID), ancl purge and trap gas chromatography-mass spectrometry (P&T-GC-MS) have been used to determine methyl-tert-butyl ether (MTBE) and benzene, toluene, and the xylenes (BTEX) in groundwater. In the work discussed in this paper measures of quality, e.g. recovery (94-111%), precision (4.6 -12.2%), limits of detection (0.3 -5.7 I~g L 1 for HS and 0.001 I~g L 1 for PT), and robustness, for both methods were compared. In addition, for purposes of comparison, groundwater samples from areas suffering from odor problems because of fuel spillage and tank leakage were analyzed by use of both techniques. For high concentration levels there was good correlation between results from both methods. Results from P&T analysis showed that 20 of the 21 samples from the vulnerable areas contained MTBE at concentrations up to 666 I~g L 1. Levels in seven samples exceeded maximum permissible levels for odor and taste set by the USEPA (20 -40 I~g L 1); for thirteen of the samples levels were bel',,veen 0.28 and 179 I~g L 1. The sensitivily of HS-GC-FID was, however, I',,vo to three orders of magnitude lower and concentrations of 6-10 I~g L 1 could not always be detected, leading to false negatives. The same behavior was observed for analysis of BTEXthe lower sensitivity of HS-GC-FID and coelution of peaks led to results of poor rehabihty, and confirmation by GC-MS was always necessary. The applicability of I',,vo analytical methods widely used for routine monitoring of VOC thus depends on the organoleptic thresholds of MTBE and BTEX in groundwater (20 I~g L 1) and the need to survey trace concentrations of persistent MTBE in vulnerable aquifers.

The geometrical isomers of carotenoids are now attracting considerable interest, due in part to the fact that they are known to behave differently in terms of susceptibility to oxidation, vitamin A activity and bioavailability. The study of such isomers has been facilitated by the development of the C30 stationary phase, which has made it possible to evaluate their occurrence in

We provide a detailed description of a model and its computational algorithm for the secondary electron emission process. The model is based on a broad phenomenological fit to data for the secondary emission yield (SEY) and the emitted-energy spectrum. We provide two sets of values for the parameters by fitting our model to two particular data sets, one for copper and the other one for stainless steel.

A comprehensive study of the stress release and structural changes caused by postdeposition thermal annealing of tetrahedral amorphous carbon (ta-C) on Si has been carried out. Complete stress relief occurs at 600–700 °C and is accompanied by minimal structural modifications, as indicated by electron energy loss spectroscopy, Raman spectroscopy, and optical gap measurements. Further annealing in vacuum converts sp3 sites to sp2 with a drastic change occurring after 1100 °C. The field emitting behavior is substantially retained up to the complete stress relief, confirming that ta-C is a robust emitting material.

In the dlssociatlvc cxcitatlon of hydrogen contaimng molcculcs by clcctron Impact. the decay curves of th.: rcstdting 11, Intcnsitics have been mcawrcd by means of rl dclaycd comcidcncc tcchniquc. WC dctcrmmed the contribution of the tfIc stntc to the total II, emission intensity by analy\ls of thcsc decay curves. The molcculcs urd in this work arr, Ef2,_EIC!, 1120, Nil-and Cila. Our cxocriment.rl results are in ac!rccment with those found prcviourly by means of tRc appIic.ltiun of the Starkicvcl mivi& effect:

Ionization of aliphatic and aromatic aldehydes is improved by performing simultaneous chemical derivatization using 4-aminophenol to produce charged iminium ions during paper spray ionization. Accelerated reactions occur in the microdroplets generated during the paper spray ionization event for the tested aldehydes (formaldehyde, n-pentanaldehyde, n-nonanaldehyde, n-decanaldehyde, ndodecanaldehyde, benzaldehyde, m-anisaldehyde, and p-hydroxybenzaldehyde). Tandem mass spectrometric analysis of the iminium ions using collision-induced dissociation demonstrated that straight chain aldehydes give a characteristic fragment at m/z 122 (shown to correspond to protonated 4-(methyleneamino)phenol), while the arylaldehydeiminium ions fragment to give a characteristic product ion at m/z 120. These features allow straightforward identification of linear and aromatic aldehydes. Quantitative analysis of n-nonaldehyde using a benchtop mass spectrometer demonstrated a linear response over 3 orders of magnitude from 2.5 ng -5 µg of aldehyde loaded on the filter paper emitter. The limit of detection was determined to be 2.2 ng for this aldehyde. The method had a precision of 22%, relative standard deviation. The experiment was also implemented using a portable ion trap mass spectrometer.

The x-ray reaflectivity of the VETI'A-I optic, the outermost shell of the AXAF x-ray telescope, with a bare 7_erodur surface, is measured and compared with theoretical predictions. Measurements made at energies of 0.28, 0.9, 1.5, 2.1, and 2.3 keV are compared with predictions based on ray trace calculations. The data were obtained at the x-ray calibration facility at Marshall Space Flight Center with an electron impact x-ray source kr.ated 528 m from the grazing incidence mirror. The source used photoelectric absorption filters to eliminate bremsstrahlung continuum. The mirror has adiameter of 1.2 m and a focal length of 10 m. The incident and reflected x-ray flux are detected using two proportional counters, one located in the incident beam of x-rays at the ennance apernue of the VErA-I, and the other in the focal plane behind an apertureof variable size. Results on the variation of the reflectivity with energy as well as the absolute value of the roflectivity are presented. We also present a synchrotrm mflectivity measurement with high energy resolution over the range 0.26 to 1.8 keV on a flat Zeredur sample, done at NSLS. We present evidence for contamination of the flat by athin iayer of carbon on the surface, and the possibility of alteration of the surface composition of the VETA-I mirror perhaps by the polishing technique. The overall agreement between the measured and calculated effective area of VETA-I is between 2.6% and 10%, depending on which model for the surface composition is adopted. Measurements at individual energies deviate from the best-fitting calculation to 0.3 to 0.8%, averaging 0.6% at energies below the high energy cutoff of the mirror reflectivity, and are as high as 20.7% at the cutoff. We also discuss the approach to the fired preflight calibration of the full AXAF flight mirror.

We report differential elastic cross sections for low-energy electron scattering by CHF 3 , CH 2 F 2 , CH 3 F, CHCl 3 , CH 2 Cl 2 , CH 3 Cl, CHCl 3 , CF 2 Cl 2 , and CF 3 Cl, obtained with the Schwinger multichannel method with norm-conserving pseudopotentials. Our results are in excellent agreement with available experimental and theoretical data. We compare the present results with our previous results for CH 4 , CF 4 , and CCl 4 and show that the oscillatory behavior of the cross sections is related to electron scattering from heavier centers ͑F or Cl͒, which favors the coupling of high partial waves. We also include a table with momentum-transfer cross sections. ͓S1050-2947͑99͒02801-2͔

We calculate electronic excitation cross sections for the b 3 ⌺ u ϩ a 3 ⌺ g ϩ c 3 ⌸ u , and d 3 ⌸ u states of H 2 by electron impact. Our results were obtained with the Schwinger multichannel method with pseudopotentials and real potentials at the two-channel level of approximation. Pseudo-H atoms are used to generate H 2 molecules with almost the same low-energy spectrum as the real molecules. We show that the dynamics of the electronic excitation process of the pseudomolecules by electron impact is very similar to the real case. Our results support the idea that pseudopotentials can be used to obtain reliable molecular electronic excitation cross sections by low-energy electron impact, confirming the expectations of previous studies with CH 2 O ͓Bettega et al.,

Ab initio cross-section calculations of low-energy e -molecule scattering have been limited to molecular targets composed of atoms with few electrons. We use soft norm-conserving pseudopotentials in both the target description and the scattering calculations to study molecules with hundreds of electrons. Comparison with all-electron calculations and crossed-beam experiments for the smallest molecule proves the high quality of the combined pseudopotentialab initio technique. Our results for all other molecules compared to experimental data indicate that we have a very promising technique.

Metabolic dealkylation and hydroxylation reactions in xenobiotics are common and may take place at different sites in the molecules. Sometimes confusion may arise as to the nature and site of the resulting metabolic change when there is more than one potential site. The use of GC-MS in resolving the problem has been demonstrated by using tramadol as example. Human urine samples containing tramadol and its metabolites were extracted under basic pH conditions and analyzed by GC-MS, in the electron impact and chemical ionization modes, before and after trimethylsilyl (TMS) derivatization. By recognizing the mass-tocharge ratios of molecular and base-peak ions in the mass spectra, it was possible to predict and designate sites of demethylation and hydroxylation in tramadol metabolites. In addition to the designation of the known tramadol metabolites, the practice has led to the tentative characterization of hydroxytramadol and norhydroxytramadol as new metabolites of tramadol in humans. Possible extension of the modus operandi to other xenobiotics was discussed.

Metabolic dealkylation and hydroxylation reactions in xenobiotics are common and may take place at different sites in the molecules. Sometimes confusion may arise as to the nature and site of the resulting metabolic change when there is more than one potential site. The use of GC-MS in resolving the problem has been demonstrated by using tramadol as example. Human urine samples containing tramadol and its metabolites were extracted under basic pH conditions and analyzed by GC-MS, in the electron impact and chemical ionization modes, before and after trimethylsilyl (TMS) derivatization. By recognizing the mass-tocharge ratios of molecular and base-peak ions in the mass spectra, it was possible to predict and designate sites of demethylation and hydroxylation in tramadol metabolites. In addition to the designation of the known tramadol metabolites, the practice has led to the tentative characterization of hydroxytramadol and norhydroxytramadol as new metabolites of tramadol in humans. Possible extension of the modus operandi to other xenobiotics was discussed.

In this study, we report the angular distribution of double dierential cross sections of ejected electrons from Ar in intermediate energy region. Double dierential cross-sections for electron impact ionization of argon have been measured at 348 eV. A hemispherical energy analyzer is used to analyze the ejected electrons with energies between 25 and 325 eV and angles between 25 • and 130 • .

Under electron impact malonaldehydedianil and its bis Co(II), Ni(II) and Zn(II) complexes produce a stable molecular ion. The Cu(I1) complex appears to decompose prior to ionization. The free dianil molecular ion fragments by expulsion of the azomethine proton or by fission of C-N bonds. The molecular ions of the metal complexes usually expel a complete ligand before undergoing demetallation.

An experimental evidence is reported on the observation of the Doppler effect in fluorine K-Auger line emitted from a core-ionized SF 6 molecule under an impact of 16 keV electrons. The emitting source of the Auger line is found to acquire a kinetic energy of 4.7± 0.3 keV. We propose that such large energy is released from the Coulomb repulsion taking place between F + and SF 5 + fragment ions under influence of an intense focusing field of the incident electrons. In the presence of the Coulomb field of these ions, the Auger line obtains a polarization P =76% ±7%.

The dissociative ionization of a N 2 O molecule is studied at an electron energy of 10 keV using the multiple-ioncoincidence imaging technique. The complete as well as the incomplete Coulomb explosion pathways for N 2 O 2+ and N 2 O 3+ ions are examined and identified. The precursor-specific relative partial ionization cross sections for resulting fragment ions are obtained. It is found that about 81.8% of single ionization, 17.8% of double ionization, and about 0.4% of triple ionization of the parent molecule contribute to the total fragment ion yield. Furthermore, the relative ionic fractions for ion-pair and ion-triple formation are also determined. The kinetic energy release distributions for different coincidence channels are obtained and compared with the available data at lower energies of electron and photon impacts and with that of high-energy ion impact. From the angular correlation studies of fragment ions, it is inferred that states with bent geometries are involved for most of the fragmentation channels of N 2 O 2+ and N 2 O 3+ ions. The concerted and/or sequential nature of the six dissociation pathways is also assigned. No other experimental or theoretical data exist in the literature to compare with the results obtained at the considered impact energy.

A time-of-flight spectrometer has been designed and fabricated for measuring the charge state distributions of target ions produced in collisions of keV-electrons with gaseous target atoms/molecules. The design details of the spectrometer and the description of experimental procedures for optimizing various parameters are presented and discussed. The working principle of the spectrometer, its time-and mass-focussing conditions, transmissions and detection efficiency etc. are given. A few typical test runs on multiple ionization of Ne and Ar gas atoms are illustrated. These spectra are found to yield the time resolution of about 10 ns for Ar 4• ion peak in 24.0 keV e -Ar collisions while the mass resolution of the spectrometer is obtained about 10% at mass m 20.

The dynamics of ionic fragmentation of CH 4 molecules under impact of 10-keV electrons has been studied. The technique of recoil ion momentum spectroscopy is employed to obtain information about the kinetic energy release and the dissociation mechanisms of different pathways arising from the fragmentation of a CH 4 dication. The results show that there are altogether eight dissociation pathways that arise from the complete and the incomplete Coulomb explosions of the CH 4 2+ molecular ions. The kinetic energy release for these pathways is compared with earlier data from the literature for the impact of different charged particles, photons, and their impact energies. The present results indicate that mostly the lower electronic states of CH 4 2+ are involved for the observed dissociation channels. Also, the dissociation mechanisms associated with these channels are suggested and discussed. Further, we have also estimated the relative ion intensities of different channels of fragmentation of CH 4 dication produced under impact of considered energy of electrons.

The electron-impact multiple ionization and subsequent dissociation of CO 2 is studied for 12-keV electron energy using a linear time-of-flight mass spectrometer coupled with a multihit, position-sensitive detector. The complete as well as incomplete Coulomb explosion pathways for CO 2 2+ and CO 2 3+ ions are examined and identified. The kinetic energy release distributions for these precursor ions are obtained. The experimental kinetic energy release values for the complete Coulomb fragmentation channels are found to be overestimated by those calculated from the Coulomb explosion model. From the angular correlation studies, it is inferred that bent geometrical states are involved for most of the fragmentation channels of CO 2 2+ and CO 2 3+ ions. The concerted and/or sequential nature of all the dissociation pathways is also assigned. This study provides the first results on energetics associated with the charge separation in dissociative ionization of CO 2 under the impact of electrons at a subrelativistic energy.

The ionic fragmentation of a multiply charged CO molecule is studied under impact of 10-keV electrons using recoil-ion momentum spectroscopy. The kinetic-energy-release distributions for the various fragmentation channels arising from the dissociation of CO q+ (q = 2-4) are measured and discussed in light of theoretical calculations available in the literature. It is observed that the present kinetic-energy-release values are much smaller than those predicted by the Coulomb explosion model. The kinetic-energy-release distribution for the C + + O + channel is suggested to arise from the tunneling process. It is seen that the peak of kinetic-energy-release distribution is larger for that dissociation channel that arises from the same molecular ion which has higher charge on the oxygen atom. Further, the relative ionic fractions for seven ion species originating from ionization and subsequent dissociation of the CO molecule are obtained and compared with the existing data reported at low energy of the electron impact. The precursor-specific relative partial ionization cross sections are also obtained and shown to be about 66.4% from single ionization, 29.9% from double ionization, 3.3% from triple ionization, and about 0.4% from quadruple ionization of the precursor CO molecule contributing to the total fragment ion yield.

The relative differential partial ionization cross sections for the production of ionic fragments of SF 6 molecule under impact of 10-20 keV electrons have been measured using an ejected electron-produced ion coincidence technique in a crossed beam apparatus with a time-of-flight analysis of the ions. The detection angle of the ejected electrons of nondiscriminated energies was kept at 90°with respect to the incident electron-beam direction. The 14 ionic fragments: SF 5 ϩ , SF 4 ϩ , SF 3 ϩ , SF 2 ϩ , SF ϩ , S ϩ , F ϩ , SF 4 2ϩ , SF 3 2ϩ , SF 2 2ϩ , S 2ϩ , F 2ϩ , SF 3 3ϩ , and S 3ϩ resulting from the dissociative ionization of the SF 6 molecule were identified and their relative production cross sections have been measured. The branching ratios of 8 ionic fragments SF m nϩ (mϭ1 to 5 and nϭ1 to 3͒ as a function of impact energy have been determined. These ratios are found to have an almost a constant value over the considered impact energy range within the experimental uncertainty of the measurements. For the investigated impact energies, no previous data or theoretical calculations exist for a direct comparison with the present results.

An experimental evidence is reported on the observation of the Doppler effect in fluorine K-Auger line emitted from a core-ionized SF6 molecule under an impact of 16keV electrons. The emitting source of the Auger line is found to acquire a kinetic energy of 4.7±0.3keV. We propose that such large energy is released from the Coulomb repulsion taking place between F+ and SF5+ fragment ions under influence of an intense focusing field of the incident electrons. In the presence of the Coulomb field of these ions, the Auger line obtains a polarization P=76%±7%.

Cross sections for rotational excitation and de-excitation of the HeH+ ion by an electron impact are computed using a theoretical approach that combines the UK R-matrix code and the multi-channel quantum defect theory. The thermally-averaged rate coefficients derived from the obtained cross sections are fitted to an analytical formula valid for a wide range of temperatures.

This study investigates the elastic scattering of electrons and positrons by carbon dioxide (CO 2 ) molecules over a wide energy range from 1 eV to 1 KeV. We have computed differential and integral elastic cross-sections (DCS and ICS) using partial wave analysis and compared the theoretical results with available experimental data. Our findings show a strong correlation with experimental results, particularly at mid to high-energy ranges, validating the employed theoretical frameworks. Additionally, the Sherman function was examined to explore spin polarisation effects during scattering events. This research provides crucial insights for applications in atmospheric physics, materials science, and molecular scattering processes, demonstrating its direct relevance to real-world problems and paving the way for further investigation into particle-molecule interactions.

The eight members of two classes of heterocyclic isomers, namely 3‐methyl‐1,2‐, 1a‐d and 2‐methyl‐1,3‐thiazolopyridines 2a‐d have been characterized by mass spectrometry under electron ionization. High internal energy ions formed in the source have been studied by low and high resolution mass spectrometry.The data show remarkable differences among the various components of each class depending on the position of the nitrogen in the pyridine ring. Furthermore, by comparing the mass spectra of members of series 1 with those of their corresponding isomers belonging to series 2, it is still possible to obtain evidence for different behaviors in the fragmentation pathways. It seems to exclude the occurrence of inter‐conversion phenomena from one isomer into another, as well as conversion to a common intermediate before fragmentation. This also suggests that each member of series 1 and 2 retains its own structure after electron ionization.The data obtained on a double focusing instrument ...

In this work, we present an amelioration of the Dimirijević 84 formula of electron collisional Stark line widths based on modification of the semi empirical approach using collision strength values between initial, final and their perturbing levels. We have applied this method for calculation of Stark widths of some lines of neon. The obtained results were compared with experimental and other theoretical results.

For momentum transfers of order 6 A nondipole transitions can make the same contribution to inner-shell energy-loss spectra as dipole transitions. Nondipole transitions are particularly significant when there is a high density of dipole-forbidden states in the near-threshold region. %e have studied the near-threshold region in the excitation of molybdenum 3d and the excitations of 2p electrons in TiO, and SiC as a function of scattering wave vector q. At large q dipole-forbidden monopole transitions become visible as a sharp peak on the Mq 5 threshold for molybdenum corresponding to 3d ~4d transitions or as a change in the L& 3 peaks intensity ratio in the cases of titani- um and silicon. Experimental results are confirmed by calculations.

Compelling evidence indicates that endocannabinoids are implicated in drug addiction. In the present study, we have addressed the interaction between cocaine and endocannabinoid system by means of neurochemical and neurophysiological experiments in rat brain slices. Using gas chromatography-electron impact mass spectrometry, we have found that cocaine increased the levels of the endocannabinoid anandamide in the striatum, a brain area primarily involved in the compulsive drug-seeking and drug-taking behaviors typical of addiction. This effect was attenuated by pharmacological inhibition of D2-like receptors but not D1-like receptors, and it was mimicked by D2-like but not D1-like receptor stimulation. The cocaine-induced increase in anandamide concentrations was attributable to both stimulation of its synthesis and inhibition of its degradation, as suggested by the ability of cocaine and quinpirole, a D2-like receptor agonist, to enhance the activity of NAPE-phospholipase D and to inhibit fatty acid amide hydrolase. By means of electrophysiological recordings from single striatal neurons, we have then observed that the ability of cocaine to inhibit, via D2-like receptors, GABA transmission was partially prevented following blockade of cannabinoid receptors, suggesting that endocannabinoids may act as downstream effectors in the action of cocaine in the striatum. Understanding the molecular and physiological effects of drugs of abuse in the brain is essential for the development of effective strategies against addiction.

We present an investigation of the Xe2 excimer emission spectrum observed in the near infrared range about 7800 cm -1 in pure Xe gas and in an Ar (90%) -Xe (10%) mixture and obtained by exciting the gas with energetic electrons. The Franck-Condon simulation of the spectrum shape suggests that emission stems from a bound-free molecular transition never studied before. The states involved are assigned as the bound (3)0 + u state with 6p [1/2]0 atomic limit and the dissociative (1)0 + g state with 6s [3/2]1 limit. Comparison with the spectrum simulated by using theoretical potentials shows that the dissociative one does not reproduce correctly the spectrum features.

The time-dependent description of the dynamics of electron-molecule collision complexes is out- lined within the framework of Feshbach's projection-operator formalism. It is shown that the equation of motion for the quantum-mechanical wave packet representing the collision complex contains effective-potential terms which are nonlocal as well as non-Markovian, that is, the time develop- rnent depends on the previous history of the system. The space-time integro-differential equation of motion is explicitly (numerically) solved for a class of simple models using expansions into complete sets of functions in both space and time. The exact wave-packet dynamics is compared with the re- sults obtained in the local-complex-potential approximation, which corresponds to the Markovian approximation for the decay dynamics. The concepts and numerical methods are illustrated for a model of the well-known 'll, , shape resonance in electron-N, scattering, where the boomerang effect is reproduced. For a model of a p-wave shape resonance near threshold, novel qualitative effects are revealed, namely, nonmonotonic electronic decay (recapture of electrorls from the continuum) as well as strong frictional effects i» the vibrational motion. The time-dependent description of virtual-state threshold effects in s-wave scattering is also briefly considered.

This paper studies the Yang-Lee edge singularity of 2-dimensional (2D) Ising model based on a quantum spin chain and transfer matrix measurements on the cylinder. Based on finite-size scaling, the low-lying excitation spectrum is found at the Yang-Lee edge singularity. Based on transfer matrix techniques, the single structure constant is evaluated at the Yang-Lee edge singularity. The results of both types of measurements are found to be fully consistent with the predictions for the (A4, A1) minimal conformal field theory, which was previously identified with this critical point.

Abstract. The resonant states of HeH are computed by combining structure calculations at a full configuration interaction level with electron scattering calculations carried out using the Complex-Kohn variational method. We obtain the potential energy curves, autoionization widths, as well as non-adiabatic couplings among the resonant states. Using the non-adiabatic couplings, the adiabatic to diabatic transformation matrix can be obtained. A strict diabatization of the resonant states will be used to study various scattering processes where the resonant states are involved. These processes involve high energy dissociative recombination (DR) and ion-pair formation (RIP), resonant and direct dissociative excitation (DE), penning ionization (PI) as well as mutual neutralization (MN). 1.

We have applied optical-optical-optical triple resonance spectroscopy to resolve a system of high Rydberg states in BH that serves quantitatively to characterize a fundamental example of electronorbital-cation core rotational coupling. The third-color ionization-detected absorption spectrum originating from the photoselected 3s B 1 Rydberg state with vibrational and total angular momentum quantum numbers, v 0 1 and N 0 0 consists entirely of vibrationally autoionizing resonances for which final N 1 that converge in series to the BH v 1 rotational limits, N 0, 1, and 2. For series with l 1 converging to N 0 and 2, Rydberg orbital and rotational angular momenta couple to systematically perturb level energies and distribute lifetime in a well-isolated twochannel rotronic interaction that spans hundreds of wave numbers.

Omega-3 index is a relatively new concept, defined as the sum of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) expressed as a percentage of the total fatty acids in red blood cell membranes. This index reflects medium to long-term intake of omega-3 polyunsaturated fatty acids and could be a useful tool in epidemiological studies. The standard technique used for fatty acid analysis and quantification has been gas chromatography (GC) with flame ionization detection. This method is robust and has good precision and sensitivity. However, a major disadvantage is inability to confirm spectrometrically the identity of fatty acids detected, which is important especially in complex biological samples. The current study measures omega-3 index in 12 healthy human volunteers using GC-mass spectrometry (MS). Both the intra-assay and day-to-day variations were well within 5% with linearity of response extending to a concentration of 250 mg/ml (830 mmol/L) of EPA. The limit of detection of EPA was 0.36 mg/ml (1.2 mmol/L). About 25 fatty acids were consistently detected in red blood cells from healthy volunteers including cis and trans isomers. The omega-3 index ranged from 2.4% to 6.2% among the 12 volunteers examined and there was no difference between samples taken in the fasting and postprandial states. EPA and DHA concentrations ranged from 3.53 to 105.89 mg/ml (11.7-350 mmol/L) and 12.19 to 214.42 mg/ml (37.1-652.7 mmol/L), respectively. Thus a GC-MS method has been developed for measuring the omega-3 index. Further studies are required to determine the role of this index as a predictor of disease.

A quantitative method based on gas chromatography-mass spectrometry (GC-MS) has been developed for the detection of 16 endogenous androgens in the urine of mice. The substances are extracted from 100 L urine with freshly distilled diethyl ether after alkalinisation. The substances are derivatised with a mixture of N-methyl-N-trimethylsilyltrifluoroacetamide/NH 4 I/ethanethiol (383/1/2, v/w/v) and detected by GC-MS in the selected ion monitoring mode. The results of the method validation indicate good linearity, accuracy and precision, making the method suitable for the quantification of endogenous androgens in mouse urine. The selectivity of the method showed that no interfering peaks were observed at the retention times of the analytes. The method allows for the direct quantification and identification of testosterone and 15 other endogenous androgens at low concentrations (ng/mL) in mouse urine. The applicability of the method is shown by the analysis of a mouse urine. Several endogenous steroids could be detected.

Long-lived di-and trianions have been formed from fluorofullerenes in the gas phase by electrospray ionization. Fragmentation of multiply charged anions has been induced by multiple low-energy collisions. Two complementary dissociation experiments have been conducted. Firstly, unequivocal connectivity has been established between the precursor ion and the first and second generation of its product ions. Secondly, dianions have been studied in energy-resolved collisions, allowing the elucidation of the energetic demands of the dissociations. It was possible to study dianions with odd and even F numbers, possessing even and odd electron configurations, respectively. The fragmentation behavior is governed by the electronic stability of the anionic protagonists, in that ions with the less stable odd-electron configuration dissociate into species with the more stable even-electron configuration. Dianions with an odd electron count release an F atom to turn into an even electron system while retaining the charge state. Dianions with an even electron count undergo a more energy demanding charge separation reaction (Coulomb explosion) into an F À anion and an even electron monoanion. The studied trianions behave accordingly. F 2 loss is prominent only with monoanions within an even-to-even electron fragmentation cascade. The trianions are long-lived with lifetimes of at least 0.1 s.