Sub-Doppler laser spectroscopy of H2 and D2 in the range 91–98 nm

The absorption spectra of hydrogen and deuterium have been measured in the range 91–98 nm. A narrowband extreme ultraviolet laser source is employed in combination with a molecular beam, allowing for sub-Doppler resolution and yielding linewidths of 0.23 cm−1. Transition frequencies of 291 lines of the Lyman and Werner bands are determined with an average absolute accuracy of 0.03 cm−1. The data are analyzed in a semi-empirical perturbation model, involving heterogeneous couplings between nearby lying levels of B1Σu+ and C1Πu states. This model is found to be accurate on the level of accuracy of the data obtained.