AB-INITIO CALCULATIONS OF THE VIBRONICALLY AVERAGED HYPERFINE COUPLING-CONSTANTS IN THE 1(2)PI(U)(X(2)B(1),A(2)A(1)) STATE OF THE WATER CATION

The hyperfine coupling constants (hfcc's) A(iso) and A(ij) are calcula ted for all centres of H2O+ in its two lowest lying electronic states (X(2)B(1), A(2)A(1)) at various molecular geometries by means of the a b initio multireference configuration method. The vibronically average d values of the hfcc's for the K = 0 and K = 1 levels in (H2O)-O-17 in the energy range up to 25000 cm(-1) are computed. The study shows tha t the reliable hfcc's of higher vibronic states can only be obtained i f the vibronic coupling between the two electronic states is taken int o account, while the lowest vibronic states of the X(2)B(1) are nearly unaffected by the nuclear motion. Comparisons to the isoelectronic sy stem NH2 are made.