Fluorescence quantum yields and radiative and nonradiative lifetimes of glyoxal (1A u)

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Abstract
Fluorescence quantum yields (ΦF) from single vibronic levels (SVL’s) of glyoxal have been measured between 1 and 12 mTorr. The zero‐pressure extrapolated values of ΦF decrease nearly monotonically from 0.58 for the zeroth vibrational level (00) to 0.22 for the 2181 level at Evib=2126 cm−1. From our values of ΦF and the fluorescence decay times (τF) measured earlier by Beyer, Zittel, and Lineberger (BZL), the collision‐free values of radiative (τR) and nonradiative (τNR) lifetimes have been obtained. The observed value of τR for the 00 level is 4.1 μsec, as compared to the calculated value of 15 μsec estimated from integrated absorption by BZL. Since the observed values of ΦF are considerably greater than what had been estimated earlier, the new values for the nonradiative rate (kNR) are correspondingly smaller. The out‐of‐plane deformation mode (ν′8) is most effective as an inducing and promoting mode.