Lifetimes of fine structure levels of metastable H2 in the c 3Πu state

Abstract

Lifetimes of fine structure levels of the v=0 level of the metastable c 3Πu state of H2 are calculated by considering both the forbidden predissociation and the forbidden radiative transition to the same dissociative b 3Σu+ state as the competing decay processes. The decay rate Wp due to forbidden predissociation is calculated for the rotational level N=1 of ortho-H2 and N=2 of para-H2. The weak spin–orbit and spin–spin interactions are the perturbative interactions to mix the metastable c 3Πu state with the repulsive b 3Σu+ state. For the fine structure levels J=N, the forbidden predissociative decay rate Wp calculated is approximately 14 times larger than the previously calculated radiative decay rate Wr. The resulting lifetimes for these J=N levels (which are 0.12 msec for N=1 and 0.11 msec for N=2) are shorter than the detection limit of Johnson’s time of flight experiment. For the fine structure levels J=N±1, Wp is approximately 1/3 of Wr (except for case J=N−1=0, where Wp=0) and the resulting lifetimes vary from 1.3 to 1.4 msec. The lifetimes of non-metastable levels which predissociate via the strong Λ-doubling (or orbit–rotation) interaction are also calculated. They are 1.36×10−9 sec for N=1 of para-H2 and 4.52×10−10 sec for N=2 of ortho-H2.