Dynamics of the E state of HBr and DBr: Evidence for the role of tunneling

The dynamics of the interaction of the Rydberg E(1Σ+) state and the valence state V(1Σ+) of HBr and DBr were investigated using a reflectron time-of-flight mass spectrometer coupled with a femtosecond laser system. Interrogation of the state formed by the avoided crossing of the Rydberg and valence states revealed dynamic behavior that was different for the two isotopes. Pump–probe experiments on HBr showed no change in the lifetime over the range of pump wavelengths of 256.7–254.7 nm. However, the lifetime of DBr decreased as the pump wavelength was tuned bluer. Tunneling is involved in the evolution of the population in photoexcited Rydberg state to the ion-pair state.