Electronic states and potential energy surfaces of AgH sub 2 : Comparison with AuH sub 2

Complete active space MCSCF (CASSCF) followed by second-order configuration interaction (SOCI) and multireference single plus double configuration interaction (MRSDCI) which include excitations from the d shells are carried out on the two low-lying states of AgH{sub 2} ({sup 2}B{sub 2} and {sup 2}A{sub 1}). The bending potential energy curves of the two states with bond lengths optimized for all angles are presented. The {sup 2}B{sub 2} surface contains a double minimum with acute and obtuse H-Ag-H angles. The {sup 2}A{sub 1} surface contains a large barrier for the insertion of an Ag({sup 2}S) atom into H{sub 2} to form the linear {sup 2}{Sigma}{sup +} state of AgH{sub 2}. The excited Ag({sup 2}P) atom spontaneously inserts into H{sub 2} to form an acute-angled weak complex of Ag with H{sub 2} and another more stable {sup 2}B{sub 2} state with obtuse bending angle. The d shell correlation lowers the {sup 2}B{sub 2} obtuse-angled structure significantly. The potential energy surfaces and electronic states of AgH{sub 2} are compared with those of AuH{sub 2}. Relativistic mass-velocity effects are significant for AuH{sub 2} in comparison to AgH{sub 2}, while d correlation effects are more significant for AgH{sub 2} in comparison to AuH{sub 2}. The Mullikenmore » population analyses of the electronic states of AgH{sub 2} reveal considerable 5p participation. The bending potential energy surfaces of the {sup 2}B{sub 2} and {sup 2}A{sub 1} states of both the molecules cross, which would lead to avoided crossing of the {sup 2}E{sub {1/2}} components if the spin-orbit term is included. The effect of f-type polarization functions is also investigated by carrying out MRSDCI calculations which included the ten-component f functions in the basis sets.« less