Overtone spectroscopy of methyl C–H stretch vibration in CH3CF2Cl and CH3CFCl2

Abstract

Photoacoustic spectra of the second (3νCH), third (4νCH), and fourth (5νCH) overtones of the methyl C–H stretches in CH3CF2Cl and CH3CFCl2 were measured. The spectra are characterized by a multiple peak structure of partially resolved triplets and quartets with an anomalous linewidth decrease in the 4νCH region. The results are interpreted in terms of a simplified local mode model for C–H stretching vibrations, including also the stretch-deformation Fermi resonances. The model accounts for most spectral features and allows determination of the time scale for vibrational redistribution.

Vibrationally Mediated Photodissociation of Jet-Cooled CH3CF2Cl: A Probe of Energy Flow and Bond Breaking Dynamics

“…Previously we also measured the room-temperature PA vibrational spectra in the second (3ν CH ), third (4ν CH ), and fourth (5ν CH ) CH 3 overtones of CH 3 CF 2 Cl (HCFC 142b) and found out that they were characterized by a multipeak structure that was attributed to strong coupling between the zeroth order C-H stretch and deformation states that generated the observed mixed eigenstates. 29 A simplified local mode (LM) model was used by us to assign the spectra. The LM model, based on the model of Duncan et al, 30 included Darling-Dennison resonances between the C-H stretches and stretch-deformation Fermi resonances.…”

Dynamics of vibrationally mediated photodissociation of CH3CFCl2

“…and on direct photodissociation of CH 3 CFCl 2 21 at 193 nm, we report on the results of ϳ235 nm photodissociation of CH 3 CFCl 2 13,14 excited with three, four, and five quanta of C-H methyl stretches. 14,20 This molecule was chosen to study the involvement of the different PES's, to examine the role of the three-body channel in VMP and to get insight on the structural dependence of the decay mechanism. The speed distribution f (v) and anisotropy parameters, ␤, were obtained from the time-of-arrival profiles of 35 Cl and 35 Cl*.…”

“…Experimental 35 Cl and 35 Cl* ion arrival profiles, following the ϳ235 nm photodissociation of CH 3 CFCl 2 prepared in the main peak of the observed multiple peak structure of C-H ϭ3 -5 vibrational states 14,20 are displayed in Figs. 1͑a͒-1͑c͒, respectively.…”

“…1͑a͒-1͑c͒, respectively. In the case of four quanta of C-H methyl stretches, the pre-excitation of the two main peaks observed in the action spectra 20 were examined, whereas for C-H ϭ3 and 5, only the main peak was measured. No significant differences were found between the two in C-H ϭ4, therefore only the results from the main peak are presented.…”

“…14 The action spectra and the Doppler profiles of the corresponding photofragments were measured, revealing that both Cl and Cl 2 P 1/2 ͓Cl*͔ are released as a result of C-Cl bond cleavage. The action spectra were characterized by a multiple peak structure, attributed, relying on a simplified local mode model, 19,20 to couplings of C-H methyl stretches and deformations. From the area ratios of the Doppler profiles, the Cl*/Cl branching ratio was found to be ϳ0.…”