The 4875 Å Band System of <i>cis</i> Glyoxal

Abstract

The 4875 Å band of glyoxal has been photographed in absorption under high resolution and a rotational analysis carried out. The band is of type C and the principal molecular constants are: A′ = 0.9069 cm −1 , B′ = 0.1983 cm −1 , C′ = 0.1627 cm −1 , A″ = 0.8910 cm −1 , B″ = 0.2066 cm −1 , C″ = 0.1681 cm −1 , v 0 = 20 507.57 cm −1 . The A-rotational constants are smaller by a factor of ~2 than the constants found earlier for trans glyoxal. The new results are consistent with the assignment of the band to an allowed 1 B 1 – 1 A 1 (π*–n) transition of cis glyoxal. Temperature studies indicate that the cis isomer lies 1125 ± 100 cm −1 above the trans isomer. This is the first time that cis glyoxal has been detected experimentally.