Radiative and predissociative lifetimes of the V ′=0, 1, and 2 levels of the A 2Σ+ state of OH and OD

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Abstract
A direct measurement of the fluorescent decay rates of the V ′=0, 1, 2 vibrational levels of the A 2Σ+ state of OH and OD has been performed using pulsed laser excitation and at total gas pressures of less than 1 mTorr. The present experiment is the first in which lifetime measurements have been performed for individual rotational levels (N ′) of each of the three lowest vibrational states of both OH and OD and at pressures where both quenching and excitation transfer should be minimal. The radiative lifetime was found to increase slightly for the higher vibrational levels in agreement with a model of linear decrease of the transition moment with increasing internuclear separation. The measured radiative lifetimes, τV ′± (3σ), for OH were τ0=693±30 nsec, τ1=736±33 nsec and for OD were τ0 =691±27 nsec, τ1=712±30 nsec, τ2=736±39 nsec. The V ′=2 level of OH was found to be strongly predissociated with a predissociation lifetime of about 270±25 nsec at N ′=1. An analysis of the energies at which predissociation occurs leads to the conclusion that the repulsive 4Σ− state is responsible for all the observed predissociations for V ′?2 in both OH and OD.

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