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

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.

Hydroxyl Radical Kinetics in Repetitively Pulsed Hydrogen–Air Nanosecond Plasmas

“…where τ rad is the spontaneous radiative lifetime of the gas mixture [27], which, for the OH A 2 Σ + (v = 1) state, is equal to 1150 ns [28]. For this measurement, this sum is determined experimentally from the time-resolved LIF fluorescence decay curves.…”

Nanosecond plasma enhanced H2/O2/N2 premixed flat flames

“…As shown in [11], the uniformity of the large-volume plasma discharge under the low-pressure and high-temperature conditions of the plasma-flame facility is quite good. the radiative lifetime is taken from German [14]. For the spatially-resolved measurements, only one time delay (t=8 µs) between the plasma discharge and the Nd:YAG laser is reported.…”

A laser-photolysis fragment-fluorescence (LPFF) method for the detection of gaseous nitric acid in ambient air

“…OH(A) fluorescence is efficiently quenched by almost all gases (Schofield, 1979). In fact, Figure 5 indicates that, due to quenching by air, the emission lifetime is much shorter than about 690 ns, the electronic lifetime of that state (German, 1975). In order that the fluorescence emission does not coincide with the stray light at, for example, atmospheric pressure in the cell, we have worked at a (reduced) pressure of typically 8 mbar.…”