The Lyman and Werner bands of H2

Abstract

The Lyman and Werner bands of H2 have been measured under high resolution in the vacuum ultraviolet from 1000 to 1650 Å. Flash discharge spectra, both in absorption and in emission, have allowed an extension of the analysis to include most of the rotation–vibration levels of the ground state ([Formula: see text], ν = 0 to 14, J = 0 to 29). The C1Πu state has been observed from ν = 0–13, and the [Formula: see text] state from ν = 0–17, including highly rotationally excited levels for ν = 0–6. The resulting rotation–vibration energy levels are accurate to 0.1 cm−1.The agreement between observation and ab initio theory is now very good. The deviations of the vibrational levels are very close to zero for low ν, but increase to 0.3 cm−1 for high ν. The ab initio calculations are somewhat less accurate for the rotational levels. The deviations are close to zero for low J, but increase to 4 cm−1 for high J, that is, for energy levels close to the dissociation limit. It can also be seen that the convergence error in the Born–Oppenheimer calculation is small (~0.1 cm−1) at low energies, but approaches 1 cm−1 near the dissociation limit.