THE FORBIDDEN PREDISSOCIATION OF METASTABLE H-2(C(3)PI(-)(U)) MOLECULES STUDIED BY STATE-SPECIFIC LIFETIME MEASUREMENTS

Using laser induced fluorescence detection of metastable H-2(c (3) Pi(u)(-), upsilon=0-3, N=1-4) molecules in a beam at different distances from the source, the lifetime of resolved fine structure levels was determined. It was found to be much shorter for the F-2 levels (similar to 150-10 mu s for nu=0-3, respectively) than for the F-1 plus F-3 components (several hundred to 70 mu s). This is due to a forbidden (Delta N double dagger 0) predissociation by the b (3) Sigma(u)(+) state, which operates preferentially on the F-2 levels. Accurate bound-free Franck-Condon factor calculations reproduce the increasing trend of the predissociation rate in going from upsilon=0-3. The absolute predissociation rates from previous theoretical work, however, can only be brought into agreement with the experimental results if they are multiplied with a common scale factor of 38.