Infrared action spectroscopy and time-resolved dynamics of the OD-CO reactant complex

摘要

The infrared action spectrum of the linear OD-CO reactant complex has been recorded in the OD overtone region near 1.9 mum using an infrared pump-ultraviolet probe technique. The pure overtone band of OD-CO (~2v_(OD)) is observed at 5148.6 cm~(-1) and combination bands involving the simultaneous excitation of OD stretch and D-atom bend are identified 160.0 and 191.2 cm~(-1) to higher energy. Band assignments and spectroscopic constants are derived from the rotationally resolved structure of the spectra. The change in the ground state rotational constant upon deuteration demonstrates that the H/D-atom of the hydroxyl radical points toward CO in the OH/D-CO complex. Direct time-domain measurements yield a lifetime of 37(4) ns for OD-CO (2v_(OD)) prior to decay via inelastic scattering or chemical reaction. This is attributed in part to the closing of a near-resonant vibration to vibration energy transfer channel upon deuteration. Vibrational predissociation of OD-CO (2v_(OD)) proceeds by a vibration to rotation and/or translation mechanism that yields highly rotationally excited OD (v = 1) fragments. Intermolecular D-atom bend 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 < = 6 ns (laser-limited). Excitation of the D-atom bend also supplies sufficient energy to reopen the near-resonant vibrational energy transfer channel, resulting in minimal rotational excitation of the OD (v = 1) fragments. Finally, a ground state binding energy for OD=CO of D_0 < = 456 cm~(-1) is established from the OD (v = 1) product state distribution.