Abstract

Throughout the years an enormous amount of spectroscopy has been performed on molecular hydrogen, the simplest molecule. The most accurate absorption measurements of the various transition frequencies are still those of Dabrowski and Herzberg reported in 1974.¹Although recently an emission atlas of the H₂spectrum has appeared,^2,3low rotational quantum states could not be measured due to radiation trapping. For this reason we performed a new spectroscopic study of the lowest J-values of the ${\text{B}}^1{\Sigma }_{\text{u}}^{+}-{\text{X}}^1{\Sigma }_{\text{g}}^{+}$ Lyman and the ${\text{C}}^1{\Pi }_{{\text{u}}^{-}}-{\text{X}}^1{\Sigma }_{\text{g}}^{+}$ Werner band systems of H₂in the extreme ultraviolet wavelength region from 91-98 nm, measured in a sub-Doppler crossed beam configuration. In this laser-based experiment rotational lines with a linewidth of 0.23 cm⁻¹were recorded. The XUV-radiation is produced by frequency-tripling the output of a Nd: YAG pumped frequency-doubled dye-laser system in a dense xenon jet of. The H₂spectrum is recorded by 1 XUV + 1 UV photoionization while simultaneously an iodine⁴and an etalon spectrum are recorded in the visible for calibration purposes. With the etalon spectrum we compensate for nonlinearities in the wavelength scan. By using computerized linearization and interpolation the transition frequencies of the B-X (10-0) and the B-X (11-0) bands are determined to within 0.02 cm⁻¹. For the other bands investigated the absolute accuracy is 0.03-0.08 cm⁻¹. Apart from H₂also the D₂molecule has been investigated.

© 1994 IEEE