MEASUREMENT OF THE LIFETIME OF METASTABLE TRIATOMIC HYDROGEN

We measured the survival probability of the metastable (N = 0, K = 0) level of the 2p2A″2 of H3 as a function of time elapsed from formation of the molecule by probing its population with photoionization. We find lifetimes τ = 640-100+300 ns for the ground vibrational state and τ = 740-100+300 ns for the symmetric stretch-excited level. Equally short lifetimes are obtained from an analysis of the photoinduced bleaching of the spontaneous dissociation signal of metastable H3. These lifetimes are about 2 orders of magnitude shorter than those expected on the basis of the allowed radiative transition 2p2A″2→2s2A′ 2. We attribute the faster decay channel to weakly allowed radiative transitions between the metastable state and the degenerate mode-excited repulsive ground state of H3, as well as to predissociation of the metastable levels by the repulsive ground state of H3 induced by spin-orbit coupling. © 1990 American Institute of Physics.