Electronic relaxation of 1B3u(nπ*) pyrazine in a supersonic jet:Rotational state dependence of the nonradiative rate leading to biexponential decay

The decay of single rotational levels of the vibrationless first excited singlet state of pyrazine (1,4‐diazabenzene) following expansion in a helium supersonic jet and excitation with a pulse dye laser is biexponential, as it is for single vibronic level excitation in the bulk gas phase. However, both the relative contribution and the lifetime of the fast, ’’nonradiative’’, component are strongly dependent on the initial rotational state. A fit to the data shows that the rate of nonradiative decay is proportional to K2, where K is the projection of the rotational angular momentum vector on the (near‐symmetric) top axis. Both the interpretation of these results and their implications with respect to the theory of radiationless transitions are discussed briefly.(AIP