Nonadiabatic effects on the positions and lifetimes of the low-lying rovibrational levels of the GK 1 Σ+g and H 1 Σ+g states of H 2

The term values of rovibrational levels of the GK 1 Σ+g and H 1 Σ+g states of H 2 have been measured with absolute and relative accuracies down to 10 −4 cm −1 (≈3 MHz) and 10 −6 cm −1 (≈30 kHz), respectively, by measuring transitions to long-lived high- n Rydberg states using single-mode cw laser radiation and a collimated supersonic beam of cold H 2 molecules. The term values are compared with those determined in earlier experimental and theoretical investigations and the comparison points at discrepancies and a need for improved theoretical treatments of nonadiabatic, relativistic and radiative corrections for these states. The lifetimes of several low-lying rovibrational levels of the GK, H and I + 1 Π g states have been determined in pump–probe experiments. These lifetimes reveal a significant dependence on the electronic, vibrational and rotational excitation and also deviate from results obtained in earlier experimental and theoretical investigations.