Vibrational predissociation in van der Waals complexes of glyoxal with Ar and Kr

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Abstract
Vibrational predissociation (VP) of glyoxal–Ar and glyoxal–Kr complexes formed in a supersonic expansion has been studied in several vibrational levels of the first excited singlet electronic state S1 (1Au) of glyoxal. Analysis of the fluorescence spectrum, together with lifetime measurements, has shown that VP is in competition with other intramolecular vibrational energy redistribution processes in these systems, as well as intersystem 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 complexes), and Kr does not seem to enhance ISC. A comparison with collisional results is presented. Another interesting result of this work is that 710, a forbidden transition of free glyoxal, was found in the excitation spectrum of complexed glyoxal. The corresponding 7̄01 emission line of the complex was also observed, as well as combination bands. This suggests a strong interaction between mode 7 and one of the van der Waals modes. This interaction is the basis for a simple theoretical model which reproduces the experimental lifetime of the excited complex (7̄2).