Potential energy surfaces for the molybdenum + hydrogen reaction: collinear versus perpendicular collisions

Abstract

The potential energy surfaces (PES) of 16 electronic states for the Mo + H{sub 2} reaction are studied in two modes of collisions, namely collinear (C{sub {infinity}{nu}}) and perpendicular (C{sub 2{nu}}) modes, using the complete active space MCSCF (CASSCF) followed by multireference singles + doubles configuration interaction (MRSDCI) method. The effect of spin-orbit coupling on the ground state of MoH{sub 2} is also addressed by use of the relativistic CI (RCI) method. In the insertion mode (C{sub 2{nu}}), the {sup 7}S ground state of Mo has to surmount a barrier of 89 kcal/mol to insert with H{sub 2} to form the linear {sup 7}{Sigma}{sub g}{sup +} MoH{sub 2} state, while the b{sup 5}D (4d{sup 5}5s{sup 1}) state of Mo inserts spontaneously into H{sub 2} to form the bent {sup 5}B{sub 2} MoH{sub 2} ground state (R{sub e} = 1.67 {angstrom}, {theta}{sup c} = 116{degree}). The other electronic states of Mo such as a {sup 5}S, a {sup 5}D, etc. insert into H{sub 2} with small barriers while a {sup 3}P, a {sup 3}D, and a {sup 1}S states insert into H{sub 2} spontaneously. The {sup 7}A{sub 1} and {sup 5}B{sub 2} curves cross at {theta} {approximately} 35{degree} which should providemore » for a channel for {sup 7}S insertion in the Landau-Zener model. In the collinear (C{sub {infinity}{nu}}) mode of collision, the Mo({sup 7}S) atom forms only a weak complex with H{sub 2} while some of the quintet and triplet states form a stronger bond with H{sub 2}. Thus Mo reacts in the insertion mode more readily than the collinear mode. Mulliken population analyses and dipole moment analyses reveal considerable ionic character of the Mo-H bonds in MoH{sub 2}.« less