Predissociation of H-3 Rydberg states - art. no. 042711

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 H-3 is moni tored in parallel with the field ionization signal. Using this spectrometer , we have measured the natural lifetime of low principal quantum number Ryd berg states nsA(1)' and npE'. For the 3sA(1)', 4sA(1)', and 5sA(1)' electro nic states, we find lifetimes decreasing with increasing principal quantum number. This is unexpected for a Rydberg series and confirms the observatio ns of a previous investigation. In addition, our experiments give direct ev idence that even very high principal quantum number Rydberg states of H-3 a re selectively subject to strong predissociation. This process appreciably shortens their natural lifetimes. In the high principal quantum number ns- and nd Rydberg series converging to the lowest ionization threshold of H-3 we find a significant variation of the predissociation yield with principal quantum number and electronic angular momentum. Windows with enhanced pred issociation in the Rydberg series are explained by nonadiabatic couplings o f the laser-prepared initial states with the repulsive ground states surfac e mediated by vibrationally degenerate mode excited 4pE' and 5pE' states. T he relevance of the H-3 predissociation mechanisms for the dissociative rec ombination of H-3(+) is discussed.