New study of the even-parity spectrum of Ca I and of the influence of collisions on high Rydberg states

A new study of the even-parity spectrum of Ca I is reported. The term assignments of the 3d 2 doubly excited configuration are discussed in relation to those of the isoelectronic sequence and to the corresponding assignments in Ti I. The significance of term-dependent contraction of the 3d orbitals in Ca I, not considered in earlier studies of this spectrum, is demonstrated from ab initio Hartree-Fock calculations, and the energies of the missing terms are estimated. The authors show that data for the members n=62 to 85 of 4snd 1 D 2 do not agree as well as originally surmised with earlier MQDT extrapolations, indicating the presence of a further perturbation. They have investigated the breakdown of the Delta J selection rule in the presence of collisions with a foreign gas. A collision-induced perturbation around n=63 of 4snd 1 D 2 is used to locate the missing 1 G 4 term of 3d 2 .