Photodissociation of CH stretch overtone excited CH3Cl and CHD2Cl(vCH=5): Cl spin–orbit branching and atomic fragment yields

Abstract

The photodissociation dynamics of CH3Cl and CHD2Cl excited through their respective fourth C–H stretch overtone transitions have been investigated by detection of ground state Cl(2P3/2), spin–orbit excited Cl(2P1/2), H, and D atomic fragments by 2+1 resonance enhanced multiphoton ionization in a time-of-flight mass spectrometer. The yield of atomic Cl fragments from the vibrationally mediated photodissociation of CHD2Cl is significantly less than for CH3Cl, more than can be accounted for from differences in the cross sections for overtone excitation. This suggests that state mixing leads to a greater amplitude of the wave function of the vibrationally excited level along the dissociation coordinate in CH3Cl than in CHD2Cl. The observed differences in the Cl spin–orbit branching in the photolysis of ground state versus vibrationally excited molecules are ascribed to differences in the nuclear dissociation dynamics, rather than access to other excited electronic states. The relative yields of H and D atoms from the photodissociation of ground and vibrationally excited CHD2Cl are also reported and discussed.