$OD-N_{2}$: INFRARED SPECTROSCOPY, POTENTIAL ANISOTROPY, AND PREDISSOCIATION DYNAMICS FROM IR-UV DOUBLE RESONANCE STUDIES

Abstract

The infrared spectrum of $OD-N_{2}$ has been obtained in the OD overtone region at $1.9 \mu m$ using an IR-UV double resonance technique. An optical parametric oscillator prepares $OD-N_{2}$ with two quanta of OD stretch, while an UV laser operating in the $OD A-X 1-2$ region promotes $OD-N_{2} (2\nu_{OD})$ to the excited A electronic state, resulting in a laser-induced fluorescence signal. A rotationally resolved infrared spectrum of the pure overtone band of $OD-N_{2}$ has been observed at $5174.0 cm^{-1}$, shifted $0.7 cm^{-1}$ to lower energy than the OD monomer $Q(3/2)$ line. Analysis of the rotational structure reveals a $P = 3/2$ projection of the total angular momentum along the intermolecular axis originating from the unquenched electronic angular momentum of OD in a linear $OD-N_{2}$ complex. A lifetime of approximately 140 ns has been measured for $OD-N_{2} (2\nu_{OD})$ by varying the time delay between the IR and UV lasers. In addition, two combination bands, involving OD stretch and geared bend excitation, have also been identified 35.1 and $40.6 cm^{-1}$ to higher energy of the pure overtone band. A surprising decrease in lifetime has been observed upon excitation of one of the combination bands. The $OD-N_{2}$ observations will be compared with previous results for $OH-N_{2}$ to provide detailed information on the anisotropy of the intermolecular potential and the vibrational predissociation mechanism.