Lifetimes of high Rydberg states of methyl halides

Abstract

The lifetimes of high Rydberg states of the methyl halides CH3I, CH3Br and CH3Cl have been studied. A pulsed dye laser tuned near half the ionization energy was used, with preprogrammed field pulses, and the high Rydberg states of the compounds in selected ranges of n values were ionized after a variable delay. Plots of the electron signal versus delay yielded information about the Rydberg state lifetime. The clearest trend was found for around n = 120–160: the lifetimes of the states decreased by more than an order of magnitude from CH3I (τ ≈12.3 μs) through CH3Br to CH3C1. Within the range studied, the theoretically predicted increase in lifetimes (n 5 or n 3) was not found, and in fact the highest group of states studied (with n > 215) exhibited for all three compounds relatively short lifetimes (≈2-3 μs), possibly due to collisional processes.