Vibrational predissociation (VP) of glyoxal complexes formed in a supersonic
expansion, has been studied in several vibrational levels of the first excited singlet
electronic state S1(1Au) of glyoxal. Light complexes as H2-glyoxal display a nice state
to state dissociation. Whereas the analysis of the fluorescence spectrum, together with
lifetime measurements, have shown that VP is in competition with other intramolecular
vibrational energy redistribution processes in these systems, as well as inter-system
crossing (ISC). Glyoxal-Ar and glyoxal-Kr behave very similarly. In particular, two
isomers exist with different dissociation schemes (but similar for the same isomer of
Ar or Kr-complex), and Kr does not seem to enhance ISC. Thus selectivity in the
dissociation routes has to be understood as a competition between these deactivation
channels.