PREDISSOCIATION OF THE ACETYLENE A1AU STATE AND ITS MECHANISM

The fluorescence excitation spectrum, the MPI spectrum, and the absorption spectrum of acetylene were observed for the à 1A u←X̃1Σg+ band system in a static gas cell and in a supersonic jet. A sudden and drastic decrease in fluorescence quantum yield, Φf, was found between the V 4K2 (46 339 cm-1) and 21V 3K0 (46 673 cm-1) sublevels. The decrease in Φf, is concluded to be due to the predissociation into C 2H + H. J dependence of Φf was found for the V 4K1 vibronic sublevel, while it is absent for the level lying above V4K1. From the observed J dependence, the predissociation mechanism was concluded to be vibrational predissociation by tunneling through a potential barrier. © 1990 American Institute of Physics.