Carbonyl and Oxygen-containing Compounds

The spectrophone technique has shown that a transient chemical species formed in the photolysis of acetaldehyde vapour, previously identified as an oxetan, is in fact the acetyl radical formed by the sensitized decomposition of trace amounts of biacetyl,84 and the involvement of biacetyl in the photodecomposition of other simple aliphatic carbonyl compounds may be much more important than has been realized hitherto. 

Because of the lack of structure in the absorption spectra of many simple carbonyl compounds, excitation of individual vibronic features is rarely possible. However, in simple aldehydes such as glyoxal and methylglyoxal (pyruvaldehyde)96 and propynal, 6 as indeed for formaldehyde (discussed above), such studies are possible and have recently been reported. 

In the study on propynal vapour, 6 the observed behaviour was explicable in terms of a simple model [(34)—(42)], for which individual rate-constants were 

The luminescence decay characteristics of biacetyl vapour have also been studied at low pressures as a function of excess energy.66 Kommandeur et al. showed that at very low pressures the decay of the optically excited 1 states into isoenergetic Aul states is reversible, giving rise to two components in the fluorescence decay, viz. a short (nanosecond) component and a longer component which is sensitive to pressure and excitation wavelength, extrapolating to a rate of 

This group of workers ignore the possible fate in the vibrationally hot triplet state of intersystem crossing to the gound state, but the data have been reconsidered in the paper by Yardley et a/. 8 to include this possibility, which seems to be plausible on both experimental and theoretical grounds, and the authors show the interpretation to be consistent also with the spectrophone measure- 

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