Electronic states and potential energy surfaces of selenium dihydride and dihydridoselenium(1+)

Abstract

Complete active space MCSCF (CASSCF) followed by second-order configuration interaction (SOCI) calculations are carried out on seven electronic states of SeH/sub 2/ and the lowest state of the SeH/sub 2//sup +/ ion. The potential energy surfaces of three electronic states (/sup 1/A/sub 1/, /sup 3/B/sub 1/, /sup 1/B/sub 1/) of SeH/sub 2/ are obtained by using the CASSCF method. The CASSCF/SOCI calculations yield a /sup 1/A/sub 1/ ground state with a Se-H bond length of 1.461 /angstrom/ and a H-Se-H bond angle of 91.5/degrees/. The SOCI bond energy D/sub 0/(HSe-H) is calculated to be 3.45 eV in excellent agreement with a recent experimental value of 3.42 eV reported by Gibson et al. The SOCI atomization energy of the SeH/sub 2/ molecule is calculated to be 6.67 eV or 154 kcal/mol. The enthalpy of formation ..delta..H/sub f/ of the SeH/sub 2/ molecule is deduced to be -51 kcal/mol. The effect of extension of basis sets on the vertical separations of the seven states of SeH/sub 2/ molecule is deduced to be -51 kcal/mol. The effect of extension of basis sets on the vertical separations of the seven states of SeH/sub 2/ considered here is studied by employing a large (5s5p8d/5s5p5d) basismore » set. The bending potential energy surfaces of SeH/sub 2/ reveal that the Se(/sup 1/D) atom inserts into H/sub 2/ spontaneously to form the bent SeH/sub 2/(/sup 1/A/sub 1/) molecule while the Se(/sup 3/P) atom has to surmount a large barrier to the insertion into H/sub 2/. The dipole moment of SeH/sub 2/ calculated by using the SOCI method employing an extended (4s4p4d) basis set is 0.712 D with the polarity Se/sup -/H/sup +/. The effect of f functions on the properties of the ground state of SeH/sub 2/ is also studied.« less