Abstract
The 3A 2( nπ*)→ 1A 1X ( T 1→ S 0) phosphorescence excitation spectrum of jet-cooled xanthione was investigated in the region 14 920–17 600 cm −1. The structure observed is shown to be due to the T 1← S 0 absorption and an assignment in terms of the vibronic structure of that band is proposed. A previous assignment of the S 1← S 0 origin is considered in detail and the transition involved is shown to be most probably due to absorption of a vibronic triplet state T 1 z,ν7 . An alternative but tentative assignment of the S 1,0← S 0,0 transition is suggested. Comparison is made with previous spectroscopic and theoretical work on the molecule and its congeners, 4H-pyran-4-thione and 4H-1-benzopyran-4-thione.
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