Photodissociation of jet-cooled vibrationally excited CHFCl2 coupled with mass spectroscopic detection of 35Cl (2P3/2) [Cl], 35Cl (2P1/2) [Cl*], 37Cl (2P3/2), 37Cl (2P1/2), 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 ∼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 ∼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.
Excitation of C-H stretch overtones of CHFCl 2 followed by ϳ235 nm photodissociation was applied to investigate the effect of internal parent excitation on the dynamics of two-and three-body photofragmentation. The ϳ235 nm photons also tagged ground Cl 2 P 3/2 ͓Cl͔ and spin-orbit excited Cl 2 P 1/2 ͓Cl*͔ state photofragments, via (2ϩ1) resonantly enhanced multiphoton ionization in a time-of-flight mass spectrometer, and monitored their time-of-arrival profiles. These profiles revealed the product velocities and angular distributions of 35 Cl and 35 Cl* and suggest the contribution of three-body decay in photodissociation of CHFCl 2 pre-excited with five quanta of C-H stretch. This is the first evidence for three-body decay in photodissociation of vibrationally excited molecules.
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