Electronic states and potential energy surfaces of AuH/sub 2/

Complete active space multiconfiguration self-consistent field (CASSCF) followed by second-order configuration interaction (SOCI) calculations as well as multireference singles and doubles CI (d-MRSDCI) including the d electrons of Au are carried out on the two low-lying electronic states (/sup 2/B/sub 2/ and /sup 2/A/sub 1/) of AuH/sub 2/. The bending potential energy surfaces of the /sup 2/B/sub 2/ and /sup 2/A/sub 1/ states with the bond lengths optimized for all angles are presented. The ground state of AuH/sub 2/ is found to be a bent /sup 2/B/sub 2/ electronic state with a bending angle of 127/sup 0/ at the d-MRSDCI level and 128/sup 0/ at the CASSCF/SOCI level. The d correlation is shown to be significant, especially for the /sup 2/B/sub 2/ (bent) state. Two linear states, namely /sup 2/..sigma../sub g//sup +/ and /sup 2/..sigma../sub u//sup +/, approximately 0.88 and 0.59 eV, respectively, above the /sup 2/B/sub 2/ bent ground state are found. The bending potential energy surfaces of the two states reveal that the ground state of the gold atom (/sup 2/S) has to surmount a large barrier (90 kcal/mol) to insert into H/sub 2/ to form the /sup 2/..sigma../sub g//sup +/ linear state while the excited /sup 2/Pmore » state of the gold atom inserts spontaneously into H/sub 2/ to form the bent /sup 2/B/sub 2/ ground state. The AuH/sub 2/ ground state is about 0.85 eV less stable than Au(/sup 2/S) + H/sub 2/ at the d-MRSDCI level while the atomization energy of AuH/sub 2/ (i.e., AuH/sub 2/(/sup 2/B/sub 2/) ..-->.. Au(/sup 2/S) + 2H) is found to be 3.71 eV.« less