Fine-structure transitions in K(4P) induced by rare gases and diatomic molecules

The energy dependence and the absolute value of the cross section for the P 1/2 to P 3/2 fine-structure transition (FST) of K(4P) induced by H 2 molecules has been measured in a crossed-beam experiment. For K(4P)-rare-gas pairs, the beam data and the theoretical results for the energy dependence of the FST cross sections are in good agreement. The discrepancy between 'bulk' experimental results and theoretical data is shown to be associated with errors in the experimental data. For the K(4P)-H 2 ,-N 2 pairs, under beam conditions, the mechanism responsible for the FST process is similar to that involved when the target is a rare gas. Under the conditions of a 'bulk' experiment, when the rotational temperature of the N 2 molecules is higher, another mechanism seems to play a role. The nature of this additional mechanism is discussed.