Systematic studies of the molecular properties of intrashell and intershell doubly excited states of C 4 + and He

The molecular (and antimolecular) properties of a large number of intrashell and intershell doubly excited states of C4+ and He are studied. By comparing a number of expectation values using wavefunctions calculated by the truncated diagonalisation method (TDM) and the group theoretic doubly excited symmetry basis (DESB) functions, the origin of the molecular properties of doubly excited states are examined. In particular, properties such as rotor structure, rotational contraction and T-doubling are inherent in the DESB approximation where the rotational energy separation is due to the bielectronic repulsion. In the full TDM calculation, it is shown that whenever intershell coupling is strong, such as in He, a molecule-like rotational expansion along a rotor series becomes possible. An extensive calculation of momentum correlation, ( p , p2 ) , has also been carried out for many intrashell and intershell doubly excited states and the results are shown to be generally consistent with the classical molecular model of Krause, Morgan and Berry.