A Test of the Influence of the Nuclear Spin in Electron Impact Excitation Processes

Abstract

The Percival-Seaton hypothesis (Percival and Seaton 1958) on the role of the nuclear spin I in electron impact excitation of atoms can be summarised as follows: during the excitation and decay processes I is assumed to be “frozen” and only the total electronic angular momentum J of the atom is changed. Between excitation and decay, however, I and J couple to give the total angular momentum F; this coupling then allows a transfer of orientation and alignment from the electronic to the nuclear spin system and vice versa. These effects can be described by “perturbation coefficients” (Frauenfelder and Steffen 1968, Steffen and Alder 1975, Blum 1981) and for collisionally oriented electronic angular momenta and unpolarised nuclear spins in general lead to a depolarisation of the emitted radiation.