A b i n i t i o potential-energy surfaces for Cd(1P)+H2=CdH(X 2Σ+)+H, HCdH(X 1Σ+g), Cd(3P)+H2, and Cd(1S)+H+H

Abstract

The outcome of laser excitation of the van der Waals CdH2 complex [which consists of a ground-state Cd(1S) atom bound to an H2 molecule] to its lowest-energy singlet state(s), which connects with Cd(1P)+H2, is examined by calculating ab initio potential-energy surfaces for the above excited singlet states, the corresponding underlying triplet states [connecting to Cd(3P)+H2 ], and the singlet ground state. It is necessary to study such a multitude of states because energetically accessible reaction products such as Cd(3P)+H2, CdH(X 2Σ+)+H, Cd+H+H, and HCdH(X 1Σ+g) connect to various surfaces. In carrying out these calculations, the lowest-energy surface of 1A1 symmetry was evaluated at nearly 1100 C2v geometries using complete-active-space self-consistent-field wave functions with a valence double-zeta and a double-zeta-plus-polarization basis set on cadmium and hydrogen, respectively. The excited singlet and triplet surfaces that correlate with 1P1 and 3PJ levels of Cd plus ground-state H2 were examined in detail along paths that flux prepared by laser excitation of the singlet surface(s) is most likely to follow. Among the photoexcited singlet states, the 1B2 surface is found to provide the most energetically attractive approach path for the excited CdH2 van der Waals complex to access geometries from which HCdH, Cd+H+H, and CdH+H can be formed via intersection and coupling with the lowest 1A1 surface. The 1B1 surface is found to be weakly attractive, and the excited 1A1 surface to be repulsive at geometries characteristic of the nascent photoexcited species. The underlying triplet surfaces are found to be repulsive (3A1), weakly attractive (3B1), and slightly more attractive (3B2) at such geometries. The repulsive 3A1 surface intersects the 1B2 surface in the latter’s entrance-channel ‘‘streambed’’; the 3B1 state intersects the 1B2 surface closer to where the 1B2 and lowest 1A1 cross. The 3A1 and 1B1 surfaces also intersect in the entrance streambed of the latter. All such triplet–singlet crossings provide paths to Cd(3P)+H2.