15min:

ILANA B. POLLACK, MARIA TSIOURIS, HELEN O. LEUNG AND MARSHA I. LESTER, Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104-6323.

Infrared action spectra of the linear OD-CO reactant complex have been recorded in the OD overtone region near 1.9 µm using an infrared pump-ultraviolet probe technique. The pure overtone band of OD-CO (2 _\mathrmOD) was observed at 5148.4 cm^-1, and combination bands involving the simultaneous excitation of OD stretch and D-atom bend were identified 200.7 and 232.1 cm^-1 to higher energy. Band assignments and spectroscopic constants have been derived from the rotationally resolved structure of the spectra. Direct time-domain measurements yielded a lifetime of 34 ns for OD-CO (2 _\mathrmOD) prior to decay via inelastic scattering or chemical reaction. This is significantly longer than the laser-limited lifetime of \leq 5 ns observed for OH-CO (2 _\mathrmOH), and is attributed to the closing of a near resonant vibrational energy transfer channel upon deuteration. Intermolecular bending excitation, which drives the structural transformation from the reactant complex to the transition state for reaction, results in a dramatic shortening of the lifetime to \leq 5 ns. Excitation of the D-atom bend also supplies sufficient energy to reopen the near resonant vibrational energy transfer channel. Finally, an OD-CO binding energy of D₀ \leq 500 cm^-1 has been established from the OD (v=1) product state distribution observed following infrared overtone excitation.