Electronic states responsible for the decomposition

The value of tai is nearly 1 at short wavelengths, while it is considerably less than 1 in the longer wavelength region. Accordingly, luminescence was not observed at wavelengths shorter than 3000 

Investigations of Borkowski and Ausloos at 3025-3340 A revealed that the emission observed was fluorescence, the yield of which increased with increasing aldehyde concentration. The pressure dependence was interpreted by the following scheme 

Rebbert and Ausloos reported that -butyraldehyde quenches the phosphorescence, but exerts no influence on the fluorescence, of acetone (excited by radiation of 3130 A wavelength). Borkowski and Ausloos reported that strong phosphorescence can be observed on irradiating n-butyraldehyde in the presence of biacetyl. The phosphorescence yield increases with increasing aldehyde concentration, and 

These observations show that energy transfer may occur from the triplet acetone to the aldehyde molecule, and that triplet biacetyl can be formed as a result of energy transfer from the excited aldehyde. However, the data available at present leave unsettled the queastion as to whether reaction (5), or (5 ) followed by (5 ), is responsible for the formation of the triplet state in the photolysis of -butyr-aldehyde. 

The increase in the yield of the induced biacetyl phosphorescence with increasing aldehyde pressure is probably due to the competition between 

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Very little is known regarding the nature of the electronic state responsible for the decomposition of other ketones. The low quenching efficiencies observed in the photolysis of 2-hexanone may be interpreted by the short-life-time of the triplet state of 2-hexanone. The similar distribution of the butene isomers found in the photolysis of 4-methyl 2-hexanone at 2537 A and in its mercury-sensitized decomposition, indicates the important role played by the triplet state in reaction II even at short wavelengths. Finally, it is to be mentioned that the presence of secondary H atoms in the y position seems to enhance the contribution of the excited singlet state to the decomposition step II. 

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