Optically enhanced electron attachment to thiophenol

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Abstract
Enhanced electron attachment to KrF excimer laser irradiated thiophenol (C6H5SH) molecules has been studied in a electron swarm experiment using nitrogen as the buffer gas. Two distinct electron attachment processes were found to be responsible for the observed large enhancement in electron attachment under different experimental conditions. One enhanced electron attachment process occurred immediately (within a few μs) after laser irradiation and is shown to be due to dissociative electron attachment to electronically excited thiophenol molecules in their first excited triplet state produced indirectly via excited singlet states reached by excimer laser irradiation. At low mean electron energies (∼0.1 eV), up to 5 orders of magnitude enhancement in electron attachment has been observed for the triplet state compared to the ground electronic state. This enhanced electron attachment decreased with (i) increasing nitrogen pressure due to quenching of the first excited singlet state of thiophenol (precursor of the triplet state) by nitrogen, and (ii) increasing time delay between laser irradiation and subsequent electron attachment to the laser-irradiated molecules. This latter observation is shown to be due to the self-(triplet–triplet) quenching of the electron attaching triplet state molecules. The second observed enhanced electron attachment process occurred at longer times (>100 μs) after laser irradiation and is attributed to the electron attachment to diphenyl disulfide (C6H5SSC6H5) produced by the interaction of thiophenoxy radicals (C6H5S ̇) formed directly or indirectly via laser irradiation.