An overlap expansion method for improving ab initio model potentials: Anisotropic intermolecular potentials of N2, CO, and C2H2 with He*(2 3S)

Abstract

An overlap expansion method is proposed for improving ab initio model potentials. Correction terms are expanded in terms of overlap integrals between orbitals of the interacting system. The method is used to improve ab initio model potentials for N2+He*(2(3)S), CO+He*(2(3)S), and C2H2+He*(2(3)S). Physical meanings of the optimization are elucidated in terms of target orbitals. Correction terms are found to be dominated by the components of HOMO, LUMO, next-HOMO, and next-LUMO on the target molecule. The present overlap expansion method using a limited number of correction terms related to frontier orbitals provides an efficient and intuitive approach for construction of highly anisotropic intermolecular interaction potentials.

Collision-Energy-Resolved Penning Ionization Electron Spectroscopy of Thiazole and Benzothiazole: Study of Ionic States and Anisotropic Interactions between a Metastable He*(23S) Atom and Hetero Cyclic Compounds

“…23 The Li model potentials can also be modified in order to give quantitative agreement between observed and calculated CEDPICS. 24 In this study, He*(2 3 S) 2D-PIESs were measured for aromatic compounds with two different heteroatoms, thiazole and benzothiazole. Although five- 25 and six-membered 26 heterocyclic compounds have been extensively studied by collision energy resolved measurements, the already investigated molecules contain just one kind of heteroatom.…”

Anisotropic Interaction and Stereoreactivity in a Chemi-Ionization Process of OCS by Collision with He*(23S) Metastable Atoms

“…The coefficients C i for the unoccupied MOs (C 5 -C 7 ) are found to be positive, which are consistent with the previous studies. [30][31][32][33] The relative ratio between the optimized K (i) parameters associated with the ionization width for producing respective ionic states Γ (i) in eq 7 is found to be K (X) :K (A) :K (B) :K (C) ) 1.0: 2.2:7.1:15.8. The increasing trend for K (i) with respect to the ionization potentials for the respective ionic states has been discussed in the previous studies.…”

“…In the occupied MOs, the coefficients C i except for C 2 show positive values. As discussed in the previous studies, [30][31][32][33] contributions of the positive coefficients for occupied MOs supplement 2s-2p hybridization effects, 21,[57][58][59] which are underestimated in the Li model potential V 0 due to the larger energy gap between the 2s and 2p orbitals of the Li atom (1.848 eV) than that of He*(2 3 S) (1.114 eV). The relatively large negative value (-1195 meV) of the optimized coefficient C 2 is somewhat confusing; however, it is supposed that this feature is caused by a subtle balance of many factors in evaluating highly anisotropic interaction as the present system.…”

“…On the basis of the discussion noted previously, − the ionization width Γ ( i ) producing each ionic state of OCS + was evaluated in the following manner; where K ( i ) is a parameter to be determined so as to reproduce observed branching ratio and collision energy dependence for respective ionic states. This treatment is based on the consideration that Γ ( i ) is mainly governed by the mutual overlap between the He 1s orbital (χ 1s ) and corresponding MOs ( φ i ).…”

Collision-Energy-Resolved Penning Ionization Electron Spectroscopy of Phenylacetylene and Diphenylacetylene by Collision with He*(23S) Metastable Atoms

“…It would be interesting to obtain information on the electronic structure of π conjugated compounds as well as anisotropic interaction around the phenyl groups and the Ct C triple bond compared with related compounds such as benzene, acetylene, biphenyl, etc. 28,[43][44][45][46]…”