Search

Vibrational energy transfer was a key property of chemical reactions that remains deeply understood. In this work, the detail information of vibrational energy transfer in aniline, N,N-dimethylaniline (DMA) and N,N-diethylaniline (DEA) were studied by femtosecond time-resolved coherent anti-Stokes Raman scattering (CARS) spectroscopy, respectively. Low frequency modes of aniline, DMA and DEA were collectively excited, the beats arising from vibrational couplings among these modes were described. With analysis of vibrational coupling, energy transfer flow from one mode to another was visualized. An investigation into the molecular structure and vibrational couplings can be found that vibrational energy transfer is related to vibrational mode symmetry. In addition, substituent groups play an important role in vibrational coupling and energy transfer of aniline, DMA and DEA. A decrease of the number of substituent vibrational modes involved in coupling and energy transfer efficiency with the increase of the amount of relative molecular mass ratio was found out. [ABSTRACT FROM AUTHOR]

Time‐resolved Raman spectroscopy has been used to simultaneously measure temperature and pressure in the TATB‐based plastic‐bonded explosive (PBX) sample under laser‐driven shock wave. Temperature and pressure have been confirmed according to the ratio of anti‐Stokes to Stokes Raman intensities and the variation of the center wavenumber of the Raman peak under shock loading, respectively. The location of the shock front has been determined according to the ratio of the spectral height of the shifted Raman peak under shock loading to that of the original Raman peak, and the velocity of the shock front has been estimated by linear fit for the locations of the shock front versus delay times. Therefore, the shock propagation in this PBX sample is characterized according to the measured temperature, pressure, and shock velocity. In addition, the correlation between the pressure and the temperature under shock waves is established, and the pressure‐dependence temperature gradient is 10.06 ± 0.67 K/GPa. [ABSTRACT FROM AUTHOR]

Shock‐driven electron redistribution of triamino trinitrobenzene has been studied by time‐resolved Raman spectroscopy and first‐principle calculation. The variation trends of electron densities of CNO2 bonds, HNH bonds and intermolecular hydrogen bonds (inter‐HB) are respectively analyzed from the Raman peak shifts and the intensity changes under shock conditions. In addition, the pressure‐dependent effective bond order is calculated by density functional theory. By combining the experimental and computational results, it is deduced that electrons redistribute mainly through two paths under shock loading. In one path, the electrons transfer from the HNH, CNH2, NO bonds, and the intramolecular hydrogen bonds (intra‐HB) to the inter‐HB; and in the other path, the electrons transfer from the NO and CC bonds to the CNO2 bonds. These results suggest that this mechanism is reversible under relatively modest shock conditions and may change the strength orders of some chemical bonds and make some chemical bonds broken easily under violent shock conditions. [ABSTRACT FROM AUTHOR]

Femtosecond time-resolved transient grating (TG) technique was employed to get insight into the photodissociation mechanism of liquid nitromethane (NM). Broadband white-light continuum was introduced as the probe to observe the evolution of electronic excited states of NM molecules and the formation of photodissociation products simultaneously. The reaction channel of liquid NM under 266 nm excitation was obtained that NM molecules in excited state S 2 relax through two channels: about 73% relax to low lying S 1 state through S 2 /S 1 internal conversion with a time constant of 0.24 ps and then go back to the ground state through S 1 /S 0 internal conversion; the other 27% will dissociate with a time constant of 2.56 ps. NO 2 was found to be one of the products from the experimental TG spectra, which confirmed that C–N bond rupture was the primary dissociation channel of liquid NM. [ABSTRACT FROM AUTHOR]

Abstract: Nanosecond time-resolved Raman spectroscopy has been performed to study anthracene films using pump-probe technique. A Raman shift at 1404cm−1, which is attributed to symmetric ring stretching mode in anthracene, was examined under laser-driven shock compression up to 1.6GPa. During the shock compression, time-resolved Raman spectra with good S/N ratios are obtained, and the shock propagation and pressure are monitored in detail. The variations in Raman spectra imply that the overall linewidth broadening is likely due to the shock pressure gradient, rather than the shock-induced temperature increase in anthracene film. [ABSTRACT FROM AUTHOR]

• Low frequency parent modes are selectively excited by time- and frequency-resolved CARS spectroscopy technique, unidirectional up-hill energy transfer is detected. • Vibrational energy transfer only occur among relevant modes or bands with same vibrational symmetry. • The efficiencies of up-hill energy redistribution decrease monotonically with the increase of the frequency differences are described. Femtosecond time- and frequency-resolved coherent anti-Stokes Raman scattering (CARS) spectroscopy is proposed to selectively excite parent vibrational modes and detect energy flow to daughter modes in liquid nitromethane (NM, CH 3 NO 2). The NO symmetric bending mode (δ s NO 2 ~657cm−1, symmetry: A 1), CN symmetric stretching mode (ν s (CN)~918cm−1, symmetry: A 1), CH 3 rocking mode (ρ(CH 3)~1104cm−1, symmetry: B 1), nitro group stretching modes (ν s (NO 2)~1379cm−1, symmetry: A 1 and ν a (NO 2)~1560cm−1, symmetry: B 1) of nitromethane (NM) are selectively excited in an orderly manner, vibrational energy flow to the neighboring higher ones located outside the excitation range is observed. Counterintuitive up-hill energy flow from lower frequency modes to higher ones is related to the vibrational symmetry. What's more, it is also found that up-hill intramolecular vibrational energy redistribution efficiencies decrease monotonically with the increase of the frequency differences. [ABSTRACT FROM AUTHOR]