INFRARED ACTION SPECTROSCOPY AND VIBRATIONAL PREDISSOCIATION DYNAMICS OF $OH-N_{2}$
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Date
2001
Journal Title
Journal ISSN
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Publisher
Ohio State University
Abstract
A sensitive IR pump - UV probe technique has been used to obtain the infrared action spectrum of $OH-N_{2}$ complexes and probe their subsequent decay dynamics. An optical parametric oscillator operating in the OH overtone region near $1.4 \mu m$ prepares $OH-N_{2}$ with two quanta of OH stretch $(2\nu_{OH})$. The $OH (v = 1)$ fragments resulting from vibrational predissociation are then detected by laser-induced fluorescence on the $OH A-X 0-1$ transition. Scanning the IR pump laser has revealed the pure OH overtone band of $OH-N_{2}$ at $6973.5 cm^{-1}$, which is shifted $2.3 cm^{-1}$ to higher energy of the $OH Q(3/2)$ line. The rotational band structure is indicative of a parallel transition for a linear $OH-N_{2}$ complex having a projection $P = 3/2$ of the total angular momentum along the intermolecular axis. The nonzero projection originates from the electronic angular momentum of OH. Several combination bands involving the simultaneous excitation of OH stretching and geared bending modes have also been identified 32.9, 38.9, and $70.6 cm^{-1}$ to higher energy of the pure overtone band. The rotational structures of these bands are characteristic of transitions to $P = 1/2$, 5/2, and 3/2 states with vibrational angular momentum from fundamental and overtone geared bending excitation. In addition, the rate of appearance of the OH fragments yields the lifetime for $OH-N_{2} (2\nu_{OH})$ of $30 \pm 4 ns$, while the OH product state distribution indicates that vibrational predissociation proceeds by a vibration-to-vibration energy transfer mechanism. The experimental measurements for $OH-N_{2}$ will be compared with previous results for closely related systems.
Description
$^{a}$Permanant address: Department of Chemistry, Amherst College, Amherst, MA 01002-5000
Author Institution: University of Pennsylvania; Department of Chemistry, University of Pennsylvania
Author Institution: University of Pennsylvania; Department of Chemistry, University of Pennsylvania