Vibrationally mediated photodissociation of CH3Cl: the v=3 and 4 CH stretch overtone levels

The photodissociation of jet-cooled vibrationally excited CH3Cl near 235 nm has been investigated by detection of the Cl(2P3/2) and Cl(2P1/2) photofragments through resonance enhanced multiphoton ionization (REMPI) in a time-of-flight mass spectrometer. Vibrationally excited molecules with three or four quanta of CH stretch excitation were prepared by irradiation with tunable near infrared (NIR) laser radiation, and a single UV laser beam was used for both photolysis and fragment detection. The action spectra of the photofragments were much more highly resolved than the room-temperature photoacoustic (PA) spectrum. The differing intensities of vibrational bands in the PA and action spectra are discussed.