The 2980 Å Absorption Spectrum of 1,2,5-Selenadiazole

The u.v. absorption spectrum of 1,2,5-selenadiazole in the 3050–2600 Å region has been recorded and, by analogy to previous studies of furazan (1,2,5-oxadiazole) and 1,2,5-thiadiazole, an interpretation of the spectrum in terms of an allowed electronic transition involving primarily activity of ν 5 , a symmetric ring in-plane bending vibration, and ν 10 , a ring out-of-plane bending vibration, has been made. This analysis indicates that the excited state is non-planar, and the barrier to planarity has been calculated to be in the order of 115 cm −1 .