Tunneling and decay dynamics of (H)over-bar(1)Sigma(+)(g) outer well states in hydrogen

We present an experimental study of the decay dynamics of rovibrational sta tes confined in the outer minimum of the <H(H)over bar> (1)Sigma(g)(+) pote ntial of the hydrogen molecule. Specific (v,J) quantum states are populated using a two-step excitation process involving a pulsed extreme ultraviolet laser source. Decay products are selectively probed with additional laser pulses, using the timing of these pulses to determine lifetimes. The compet ition between dissociation and ionization, occurring at short internuclear distance after tunneling through the potential barrier, is addressed. Obser ved lifetimes and decay channels of (H) over bar levels are consistent with a semiclassical description of tunneling of the nuclear motion through the potential barrier towards small internuclear distance. For the HD isotopom er breaking of the g-u symmetry is found to strongly affect the decay dynam ics. (C) 2000 American Institute of Physics. [S0021-9606(00)00624-3].