Further study on collisional quantum interference effect in energy transfer within CO singlet-triplet mixed states Noble gas induced collisional line broadening of atomic Li Rydberg states nS and nD (n=4 to 30) measured by trilevel echoes AIP Conf.Collision-induced vibrational energy transfer has been studied from four levels ͓30 2 ͑E vib ϭ240 cm Ϫ1 ͒, 8 2 ͑E vib ϭ361 cm Ϫ1 ͒, 27 1 ͑E vib ϭ403 cm Ϫ1 ͒ and 6 1 ͑E vib ϭ410 cm Ϫ1 ͔͒ in S 1 p-difluorobenzene in supersonic free jet expansions of He, Ne, Ar, and Kr at ϳ30-40 K. In broad terms the trends are similar to those observed previously in studies of aromatics: the transfer is highly selective, and one quantum changes in the low frequency modes are preferred. However, a significant collision partner dependence is observed, whereby changing from He through to Kr causes a substantial increase in multiple quanta ͉͑⌬͉Ͼ1͒ transfer. SSH-T calculations fail to capture this trend. The preference for ͉⌬͉Ͼ1 transfer appears to be enhanced as the interaction time and attractive force on the collision partner increase. Consequently, it is predicted that ͑i͒ differences in the state-to-state branching ratios between collision partners will increase as the temperature is lowered; ͑ii͒ for a particular collision partner there will be an increase in ͉⌬͉Ͼ1 transfer with decreasing temperature; and ͑iii͒ ͉⌬͉Ͼ1 transfers will be most important for collision partners with small velocities ͑i.e., large masses͒, large intermolecular potential well depths ͑⑀͒ and size ͑͒. The nearly isoenergetic 27 1 and 6 1 levels have virtually identical state-to-state branching ratios for Ar and small differences are observed for He. This suggests that the branching ratios are not particularly sensitive to the initial vibrational motion. Relaxation of 6 1 and 27 1 is inefficient compared with relaxation from 30 2 and 8 2 .
Collision-induced vibrational energy transfer has been studied from three levels [302 (Evib=240 cm−1), 82 (Evib=361 cm−1), and 61 (Evib=410 cm−1)] in S1 p-difluorobenzene (pDFB) in a supersonic free jet expansion using the polyatomic partners methane, ethane, cyclopropane, and i-butane. The data indicate that vibration-to-vibration transfer is not efficient. Nevertheless, significant differences are found to exist between the state-to-state branching ratios for the polyatomic partners and those observed previously for monatomic and diatomic partners, with the exception of nitrogen. For the polyatomic partners single quantum changes in low frequency modes are no longer dominant. The polyatomic partners generally display a preference for transfer via channels involving large pDFB vibrational energy loss. There are similarities in the preferred two quanta channels for polyatomic and diatomic partners.
Collision-induced vibrational energy transfer has been studied from three vibrational levels at intermediate state density in S1 p-difluorobenzene in a supersonic free jet expansion. Transfer was studied from the 51 (Evib=818 cm−1; ρvib=0.6 per cm−1), 292 (Evib=876 cm−1; ρvib=0.6 per cm−1), and 5182 (Evib=1179 cm−1; ρvib=2.3 per cm−1) levels. The collision partners include a range of monatomics, diatomics, and polyatomics for 51 and 292. Hydrogen was the collision partner for 5182. For 292, transfers involving multiple changes in vibrational quanta are important, and generally such transfers dominate. This behavior is different from that observed at low state densities but is analogous to what has been observed previously at intermediate state densities in p-difluorobenzene [Mudjijono and W. D. Lawrance, J. Chem. Phys. 108, 4877 (1998)]. There is a suggestion in the data for c-propane and ethane that transfer to vibrational modes of these collision partners is occurring. 51 shows very inefficient relaxation. With the exception of N2, there is no evidence in the spectra for significant transfer via channels involving multiple changes in vibrational quanta. The state-to-state branching ratios for transfer from 5182 were essentially in quantitative agreement with those expected based on transfer from 82. It appears that the in-plane mode ν5, and combinations involving low frequency modes with ν5, behave qualitatively differently to the lower frequency, out-of-plane modes. The lower frequency, out-of-plane modes change their state-to-state relaxation preferences with increasing vibrational state density, with multiple quantum changes becoming preferred, while the higher frequency in-plane ν5 retains the state-to-state preferences seen at low state densities.
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