Photodissociation of jet-cooled, vibrationally excited CHF 2 Cl molecules was studied in a time-of-flight mass spectrometer to elucidate bond rupture and intramolecular dynamics. The molecules were first excited with infrared photons to the Nϭ3, Nϭ7/2, and Nϭ4 C-H stretch-bend polyad components, representing stretch-bend mixed states. They were then dissociated via promotion to excited electronic states by ϳ235 or 243.135 nm photons, which also tagged 35 Cl( 2 P j ) and 37 Cl( 2 P j ) or H photofragments, respectively, by ͑2ϩ1͒ resonantly enhanced multiphoton ionization. Comparison of the photofragment yield spectra to the simultaneously measured room-temperature infrared absorption spectra revealed significant narrowing of the former due to the reduction of rotational inhomogeneous structure. These spectra, and particularly the band contraction, afforded observation of resonance splitting in the vicinity of the 3 1 , 3 4 , 4 1 , and 4 4 components, reflecting redistribution times in the range of 1-18 ps. These times manifest the vibrational redistribution of the mixed states to other states of the molecule and are longer than those for the coupling of the stretch-bend. The initial vibrational excitation enhanced C-Cl and C-H bond cleavage with the former producing both ground-, Cl 2 P 3/2 ͓Cl͔, and excited-, Cl 2 P 1/2 ͓Cl*͔, spin-orbit states. The branching ratio of Cl*/Cl was ϳ0.5 and of H/͓Cl*ϩCl͔ϳ0.1, independent on the initially prepared state, signifying preferential production of Cl photofragments and energy flow from the initially excited bond.

A double resonance scheme was employed to photodissociate jet-cooled CH 3 CF 2 Cl in a time-of-flight mass spectrometer. First, the molecule was promoted to the second (3ν CH ) or third (4ν CH ) methyl overtone by direct IR excitation. Subsequently, a UV laser beam at ∼235 nm was used to both dissociate the molecule and tag the Cl 2 P 3/2 [Cl] and Cl 2 P 1/2 [Cl*] photofragments by (2 + 1) resonantly enhanced multiphoton ionization. The photofragment action spectra revealed multiple peak structures in both overtone regions, attributed to couplings of the C-H stretches and to methyl stretch-deformation Fermi resonances. The cooling of the samples afforded narrowing of the peaks, relative to room temperature photoacoustic spectra, due to the reduced rotational and vibrational congestion, and enabled observation of a new splitting in the high frequency peak of the second overtone. This splitting apparently resulted from a local resonance of the mixed stretch-deformation state with a close lying dark state. The time scales for vibrational energy redistribution in the local resonance and between the mixed stretch-deformations were evaluated. These time scales and the measured Cl*/Cl branching ratios were compared to those of other hydrohalocarbon compounds. The Cl*/Cl ratio was also compared to that of the nearly isoenergetic vibrationless ground state 193 nm photodissociation and found to be different, demonstrating the effect of vibrational pre-excitation on the photodissociation dynamics. † Part of the special issue "Donald Setser Festschrift".