Dissociation energy of hydrogen

Abstract

The measurement of the dissociation energy of hydrogen remains an important problem in spectroscopy for comparison with theoretical calculations. We report on a preliminary determination of the dissociation energy of H from a fluorescence-excitation spectrum obtained using laser-generated tunable radiation near 85 nm. The radiation was tuned to excite the uppermost vibrational levels of the B state of H and the higher-lying dissociation continuum from the ground state X(v" = 0), while the fluorescence intensity was monitored. Features which were blended in previous work1 are resolved, and they correspond well to predicted2 R(1) and P(1) branches of the X B (v' = 38, 39) transitions, thus confirming Stwalley's identification of lines in the spectrum of H near the dissociation limit of the B state. This limit is then found by extrapolating the P(1) branch positions using Stwalley's technique,2 and from the onset of the dissociation continuum1. The B state dissociates into the products H(1s) + H(2p); therefore, the binding energy of the ground state of H is found by subtracting the Lyman-energy from the B state dissociation limit. From the extrapolation, a value of 36118.6 0.2 cm1 is obtained which agrees with Stwalley's estimate,2 and is 0.5 cm1 higher than a recent theoretical calculation by Kolos et al., and a measurement by Eyler et al. using multiphoton spectroscopy. A less precise value, found from the onset of the continuum, is limited by the presently available resolution.