Photolysis and spectroscopy of vibrationally excited C-H overtones of CHFCl₂

Photodissociation of jet-cooled vibrationally excited CHFCl₂ coupled with mass spectroscopic detection of ³⁵Cl (²P_3/2) [Cl], ³⁵Cl (²P_1/2) [Cl*], ³⁷Cl (²P_3/2), ³⁷Cl (²P_1/2), and H photofragments was performed. It enabled determination of Cl*/Cl and H/[Cl*+Cl] branching ratios and measurement of the action spectra of the N = 3, N = 7/2, and N = 4 CH stretch-bend polyads. Enhanced C-Cl and C-H bond breaking was observed for all the initially prepared C-H stretch-bend states demonstrating that energy is not preserved in the initial state but rather flows into the other part of the molecule. The yield of Cl* photofragments was found to be about half that of Cl for approximately 235 nm photolysis of vibrationally excited CHFCl₂. The action spectra are significantly narrower than the room-temperature photoacoustic spectra due to reduction of the rotational inhomogeneous structure. The action spectra also enabled one to resolve the components arising from the different isotopomers of the precursor and a resonance splitting attributed to a local resonance of the 7/2₁ polyad component with a combination of the 7/2₃ component and the ClCCl bending. This splitting reflects a approximately 3 ps period for the vibrational redistribution and indicates that the coupling of the stretch-bend mixed state to the rest of the molecule is weaker than the stretch-bend coupling itself.