Abstract
A fast-beam spectrometer is used to investigate the photofragmentation and autoionization dynamics of laser-excited triatomic hydrogen molecules. The yield of neutral products from rapidly predissociated states of is monitored in parallel with the field ionization signal. Using this spectrometer, we have measured the natural lifetime of low principal quantum number Rydberg states and For the and electronic states, we find lifetimes decreasing with increasing principal quantum number. This is unexpected for a Rydberg series and confirms the observations of a previous investigation. In addition, our experiments give direct evidence that even very high principal quantum number Rydberg states of are selectively subject to strong predissociation. This process appreciably shortens their natural lifetimes. In the high principal quantum number - and Rydberg series converging to the lowest ionization threshold of we find a significant variation of the predissociation yield with principal quantum number and electronic angular momentum. Windows with enhanced predissociation in the Rydberg series are explained by nonadiabatic couplings of the laser-prepared initial states with the repulsive ground states surface mediated by vibrationally degenerate mode excited and states. The relevance of the predissociation mechanisms for the dissociative recombination of is discussed.
- Received 13 September 2000
DOI:https://doi.org/10.1103/PhysRevA.63.042711
©2001 American Physical Society