Improved parametric fits for the HeH[sub 2] ab initio energy surface

Thesis/Dissertation · Wed Jan 01 04:00:00 EST 1992

OSTI ID:7263619

Muchnick, P

A brief history of the development of ab initio calculations for the HeH[sub 2] quasi-molecule energy surface, and the parametric fits to these ab initio calculations, is presented. The concept of physical reasonableness' of the parametric fit is discussed. Several new improved parametric fits for the energy surface, meeting these requirements, are then proposed. One fit extends the Russek-Garcia parametric fit for the deep repulsion region to include r-dependent parameters, resulting in a more physically reasonable fit with smaller average error. This improved surface fit is applied to quasi-elastic collisions of He on H[sub 2] in the impulse approximation. Previous classical calculations of the scaled inelastic vibrorotational excitation energy distributions are improved with this more accurate parametric fit of the energy surface and with the incorporation of quantum effects in vibrational excitation. It is shown that Sigmund's approach in developing his scaling law is incomplete in the contribution of the three-body interactions to vibrational excitation of the H[sub 2] molecule is concerned. The Sigmund theory is extended to take into account for r-dependency of three-body interactions. A parametric fit for the entire energy surface from essentially 0 [le]R[le][infinity] and 1.2[le]r[le]1.6 a.u., where R is the intermolecular spacing and r is the hydrogen bonding length, is also presented. This fit is physically reasonable in all asymptotic limits. This first, full surface parametric fit is based primarily upon a composite of ab initio studies by Russek and Garcia and Meyer, Hariharan and Kutzelnigg. Parametric fits for the H[sub 2](1s[sigma][sub g])[sup 2], H[sub 2][sup +](1s[sigma][sub g]), H[sub 2][sup +](2p[sigma][sub u]) and (LiH[sub 2])[sup +] energy surfaces are also presented. The new parametric fits for H[sub 2], H[sub 2][sup +](1s[sigma][sub g]) are shown to be improvements over the well-known Morse potentials for these surfaces.

• Research Organization: Connecticut Univ., Storrs, CT (United States)
• OSTI ID: 7263619
• Country of Publication: United States
• Language: English

Related Subjects

664100* -- Theory of Electronic Structure of Atoms & Molecules-- (1992-)
74 ATOMIC AND MOLECULAR PHYSICS
ENERGY
ENERGY LEVELS
EXCITED STATES
FREE ENERGY
HELIUM COMPOUNDS
HELIUM HYDRIDES
HYDRIDES
HYDROGEN COMPOUNDS
INTERATOMIC FORCES
MORSE POTENTIAL
PARAMETRIC ANALYSIS
PHYSICAL PROPERTIES
POTENTIALS
RARE GAS COMPOUNDS
SURFACE ENERGY
SURFACE PROPERTIES
THERMODYNAMIC PROPERTIES
VIBRATIONAL STATES