Abstract
The zero-field magnetic resonance spectra of the lowest triplet state of glyoxal in neat crystals and in a 3-methylpentane glass were studied. Microwave double resonance and action spectroscopy were employed to identify and characterize the emitting triplet species to be two x-traps of trans-glyoxal. The T 1 └ S 0 absorption of glyoxal was found to play a major role in the population of its lowest triplet state. This is attributed to the existence of an intersystem crossing bottleneck.