The 4875 Å Band System of cis 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, v0 = 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 1B1–1A1 (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.