Papers by Zbigniew Dreger
High Pressure Chemistry, Biochemistry and Materials Science, 1993
In this paper we discuss recent applications of luminescence spectroscopy to resolve problems con... more In this paper we discuss recent applications of luminescence spectroscopy to resolve problems concerning phosphors in crystals or dissolved in polymers. On the first two examples we treat intramolecular excitations for molecules dissolved in polymers and explain mechanisms of energy dissipation due to changes of molecular conformation. The second set of examples involve ZnS phosphors with various dopants. We establish the characteristics of the donor and acceptor states via photoluminescence, and the trap characteristics by means of thermoluminescence. We treat very briefly thermoluminescence in crystalline coronene.
The journal of physical chemistry. A, Jan 10, 2014
Raman spectroscopy was used to examine the vibrational and polymorphic behavior of 1,1-diamino-2,... more Raman spectroscopy was used to examine the vibrational and polymorphic behavior of 1,1-diamino-2,2-dinitroethene (FOX-7) to elucidate its structural and chemical stability under high pressure. Measurements were performed on single crystals compressed in a diamond anvil cell, and data were obtained over the entire frequency range of FOX-7 Raman activity. Several new features were observed with increase of pressure: (i) new vibrational peaks and discontinuity in the shifts of the peaks at 2 and 4.5 GPa, (ii) apparent coupling or mixing of several modes, and (iii) changes in the NH2 stretching spectral shape and modes shift. The spectral changes at 2 GPa, in contrast to previous reports, involved only a few peaks and likely resulted from a small molecular transformation. In contrast, changes at 4.5 GPa involved most of the modes, and the pressure for the onset and completion of the changes depended on the pressure medium. A large pressure hysteresis regarding the changes at 4.5 GPa imp...
The Journal of Physical Chemistry B, 2004
The effect of pressure on the Raman spectra of pentaerythritol (PE) single crystals was examined ... more The effect of pressure on the Raman spectra of pentaerythritol (PE) single crystals was examined up to 10 GPa. Several abrupt changes in the spectra were found at 4.6 (0.2 GPa and 6.8 (0.3 GPa. These changes occur both in the internal and external modes and indicate the onset of phase transitions. Both transitions demonstrate considerable pressure hysteresis characteristic of a first-order phase change. It is concluded that PE crystals can exist in three different phases in the pressure range up to 10 GPa. Phase I, which has the bct structure, extends up to 4.6 GPa. In phase II, the number of translationally nonequivalent molecules in a PE unit cell is likely doubled. Phase III, above 6.8 GPa, has features of a disordered structure and is associated with a large softening of hydrogen bonding.
The Journal of Physical Chemistry B, 2006
To gain insight into the anisotropic sensitivity of shocked pentaerythritol tetranitrate (PETN) s... more To gain insight into the anisotropic sensitivity of shocked pentaerythritol tetranitrate (PETN) single crystals, single-pulse Raman spectroscopy was used to examine the response of crystals shocked along the [100] (insensitive) and [110] (sensitive) orientations. High-resolution Raman spectra revealed several orientationdependent features under shock compression: (i) substantially different stress dependence of the Raman shift for the CH 2 and NO 2 stretching modes for the two orientations, (ii) discontinuity in the stress dependence of the Raman shift for the CH 2 stretching modes above 4 GPa for the [110] orientation, and (iii) large broadening for the CH 2 and NO 2 asymmetric stretching modes for stresses above 4 GPa for the [110] orientation. The present data in combination with previous static pressure results provide support for conformational changes in PETN molecules for shock compression along the [110] (sensitive) orientation. Implications of the present results for the anisotropic sensitivity of shocked PETN are discussed.
The Journal of Physical Chemistry A, 2008
Quantum chemical calculations on single molecules were performed to provide insight into the deco... more Quantum chemical calculations on single molecules were performed to provide insight into the decomposition mechanism of shocked RDX. These calculations complement time-resolved spectroscopy measurements on shock wave compressed RDX crystals (previous paper, this issue). It is proposed that unimolecular decomposition is the primary pathway for RDX decomposition in its early stages and at stresses lower than ∼10 GPa. This decomposition leads to the generation of broadband emission from 350 to 850 nm. Chemiluminescence from 2 B 1 and 2 B 2 excited states of NO 2 radicals is associated with a major portion of the experimentally observed emission spectrum (>400 nm). The remaining portion (<400 nm) of the emission spectrum primarily results from excited HONO intermediates. It is proposed that for stresses higher than 10 GPa, bimolecular reactions between radical decomposition products and unreacted RDX molecules become the dominant pathway. This radical assisted homolysis pathway is cyclic and leads to the acceleration of decomposition, with increased production of low energy NO 2 radicals. These radicals produce emission that is stronger in the long wavelength portion of the spectrum. Finally, a comprehensive chemical decomposition mechanism is put forward that is consistent with the experimental observations of shock-induced emission in RDX crystals.
The Journal of Physical Chemistry A, 2008
Pressure effects on the vibrational structure of alpha-RDX were examined using density functional... more Pressure effects on the vibrational structure of alpha-RDX were examined using density functional theory (DFT) up to 4 GPa. The calculated vibrational frequencies at ambient conditions are in better agreement with experimental data than are previous single molecule calculations. The calculations showed the following pressure-induced changes: (i) larger shifts for lattice modes and for internal modes associated with the CH(2) and NO(2) groups as compared to the pressure shifts for modes associated with the triazine ring, (ii) enhancement of mixing between different vibrations, for example, between NN stretching and CH(2) scissor, wagging, twisting vibrations, and (iii) increase in mixing between translational lattice vibrations and the NO(2) wagging vibrations, reducing the distinction between internal and lattice modes. The calculated volume and lattice constants at ambient pressure are larger than the experimental values, due to the inability of the present density functional approach to correctly account for van der Waals forces. Consequently, the pressure-induced frequency shifts of many modes deviate substantially from experimental data for pressures below 1 GPa. With increasing pressure, both the lattice constants and the frequency shifts agree more closely with experimental values.
The Journal of Physical Chemistry A, 2004
The Journal of Physical Chemistry A, 2010
Raman spectroscopy and optical imaging were used to determine the phase boundaries between variou... more Raman spectroscopy and optical imaging were used to determine the phase boundaries between various hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) polymorphs. Experiments were performed on single crystals at pressures up to 8.0 GPa and temperatures ranging from room temperature to 550 K. Several distinct pressure regions were found in the RDX response at elevated temperatures: (i) melting of R-RDX followed by decomposition, below 2.0 GPa, (ii) decomposition of R-RDX between 2.0 and 2.8 GPa, (iii) irreversible transformation of Rand γ-RDX to ε-RDX between 2.8 and 6.0 GPa, and (iv) decomposition of γ-RDX above 6.0 GPa. A triple point between the R-, γ-, and ε-RDX was found at 3.7 GPa and 466 K. The R-γ phase transition was confirmed to occur at the same pressure, ∼3.7 GPa, regardless of temperature, in the range of 295-460 K. Furthermore, it was determined that ε-RDX (i) has limited chemical stability under the pressure and temperature conditions where it is produced and (ii) decomposes according to the autocatalytic rate law. The findings reported here have provided new information about the response of RDX crystals at high pressures and temperatures.
Journal of Applied Physics, 2008
Impulsive stimulated thermal scattering (ISTS) was used to determine the complete set of second-o... more Impulsive stimulated thermal scattering (ISTS) was used to determine the complete set of second-order elastic constants for pentaerythritol tetranitrate (PETN) and cyclotrimethylene trinitramine (RDX) single crystals. Despite the weak scattering efficiency of these materials, excellent signal quality was obtained by using an optical heterodyne detection approach. The elastic constants for PETN agree well with previous values obtained from ultrasonic velocity measurements. The elastic constants for RDX are consistent with previous values obtained from ultrasonic velocity measurements and from resonant ultrasound spectroscopy, but show significant differences with values obtained from Brillouin scattering data. The present results demonstrate that the ISTS method, with optical heterodyne detection, provides a useful and accurate approach for determining the elastic constants of energetic crystals.
Journal of Applied Physics, 2011
The acoustic properties of four polymers compressed to high pressures in a diamond anvil cell wer... more The acoustic properties of four polymers compressed to high pressures in a diamond anvil cell were determined using the impulsive stimulated light scattering (ISLS) method. Despite the weak scattering efficiency of these polymers, good signal quality was obtained by using a continuous wave probe and an optical heterodyne detection. We provide, for the first time, longitudinal acoustic velocities up to 5 GPa for two thermoplasts: poly(methyl-methacrylate) and poly(styrene), and two elastomers: poly(butadiene) and triblock copolymer of polystyrene-block-polybutadiene-block-polystyrene. The longitudinal acoustic velocities for all of these polymers displayed nonlinear pressure dependence. Despite the significant differences in the initial acoustic velocities these velocities converged above 2.5 GPa. This convergence is associated with the ultimate reduction of free volume in the studied polymers. We explored the possibility of measuring shear acoustic waves in these polymers using ISLS...
Chemical Physics Letters, 2006
First-principles calculations for the vibrational frequencies of the pentaerythritol crystal are ... more First-principles calculations for the vibrational frequencies of the pentaerythritol crystal are presented, at ambient and hydrostatic pressure. The CRYSTAL03 program with the Hartree-Fock potential and B3LYP density functional were used with 6-31G and 6-31G** basis sets, respectively. The calculated OH stretching mode vibrational frequencies using this approach are about 200 cm −1 lower using CRYSTAL03 than those calculated using the Gaussian98 program. The effect of hydrostatic pressure on vibrational frequencies is calculated and compared with experimental data, up to 4 GPa. The OH-stretching mode frequency decreased as a function of increasing pressure, in agreement with experiment.
Chemical Physics Letters, 1998
We report the effect of pressure on fluorescence of two flexible dye molecules of a series of par... more We report the effect of pressure on fluorescence of two flexible dye molecules of a series of para-substituted Ž. benzylidenemalononitriles dissolved in solid poly methyl methacrylate. Under pressure these molecules exhibit a remarkable increase of intensity and slowing of excited state decay. We show that these changes can be well explained by a kinetic model in which the pressure is assumed to control the barrier for the intramolecular transformation of the flexible molecules in their excited state.
APS March Meeting Abstracts, Mar 1, 1997
APS March Meeting Abstracts, Mar 1, 1997
Polish Journal of Chemistry, 1993
The effect of pressure has been measured for two non-linear optical phenomena: second harmonic ge... more The effect of pressure has been measured for two non-linear optical phenomena: second harmonic generation (SHG) in organic crystals and one and two photon fluorescence excitations in a molecule dissolved in an organic polymer. Both sets of results are discussed in terms of theory.
The Journal of Physical Chemistry A, 2020
Despite the considerable interest in insensitive high explosives (IHE) as a safer alternative to ... more Despite the considerable interest in insensitive high explosives (IHE) as a safer alternative to conventional high explosives, a good understanding of the low sensitivity of IHEs to shock initiation is lacking. In particular, real-time measurements to directly probe the molecular-level response of shock-compressed IHE single crystals constitute an important need. To address this need, plate impact experiments were conducted to determine timeresolved changes in the Raman spectra of 1,1-diamino-2,2dinitroethene (FOX-7) single crystalsa representative IHE crystalshock-compressed up to 20 GPa longitudinal stress. The Raman measurements examined vibrational frequencies from 800 to 1500 cm −1 with 15 ns time resolution and were conducted at several peak stresses. At 4−6 GPa, two new Raman peaks appeared, in addition to the original peaks, consistent with onset of the α′−ε structural transformation reported previously in static compression work. The measured spectra indicated completion of the transformation at 10 GPa. Raman data to 20 GPa showed neither additional transformations nor any indication of chemical decomposition. This finding, though consistent with recent continuum measurements, is in marked contrast to the chemical decomposition observed at lower stresses in shock-compressed conventional high explosive single crystals. Our Raman results support the previous suggestion that strengthening of intra-and intermolecular bonds, because of the α′−ε structural transformation, plays a significant role in the insensitivity of FOX-7 single crystals to shock initiation. The present work, in conjunction with previous static compression studies, provides the first experimental insight into the molecular-level response of a shock-compressed IHE single crystal and can serve as a bench mark for theoretical studies.
Aps Shock Compression of Condensed Matter Meeting Abstracts, Jun 1, 2001
Aps Shock Compression of Condensed Matter Meeting Abstracts, Jun 1, 2001
Journal of the Chinese Chemical Society, 1995
In this paper we present two recent studies utilizing pressure tuning spectroscopy. In the first ... more In this paper we present two recent studies utilizing pressure tuning spectroscopy. In the first of these we use high pressure photoluminescence to characterize the large difference in luminescence efficiency at one atmosphere between [Ru(bpy)3]2+ and [Ru(bpy)2py2]2+ ions. The lower efficiency of the latter ion is due to dissipation of excitation energy by motion of the pyridines.The second study involves a combination of photo‐and thermoluminescence of doped ZnS phosphors of technical importance. In the phosphor doped with CI and Cu+ we demonstrate that the donors are pinned to the conduction band and the acceptors to the valence band. We invoke the presence of “deep levels” to describe the behavior of the traps. In the phosphor doped with Mn+2 plus C1‐ and Cu+ a series of traps appeared as the pressure was increased. By comparison with ZnS doped only with Mn+2 it was possible to assign some of the traps to C1‐ and others to Mn+2.
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Papers by Zbigniew Dreger