Photodissociation dynamics of CH₂ICl at 222, 236, 266, 280, and 304 nm

Abstract

Dynamics of I^∗(²P_½) formation from CH₂ICl dissociation has been investigated at five different ultraviolet excitation wavelengths, e.g., 222, 236, 266, 280, and ~304 nm. The quantum yield of I^∗(²P_½) production, φ^∗, has been measured by monitoring nascent I(²P_3/2) and I^∗ concentrations using a resonance enhanced multiphoton ionization detection scheme. The measured quantum yield as a function of excitation energy follows the same trend as that of methyl iodide except at 236 nm. The photodissociation dynamics of CH₂ICl also involves three upper states similar to methyl iodide, and a qualitative correlation diagram has been constructed to account for the observed quantum yield. From the difference in behavior at 236 nm, it appears that the crossing region between the two excited states (³Q₀ and ¹Q₁) is located near the exit valley away from the Franck Condon excitation region. The B- and C-band transitions do not participate in the dynamics, and the perturbation of the methyl iodide states due to Cl-I interaction is relatively weak at the photolysis wavelengths employed in this investigation.