J. Klos et al., Ab initio potential-energy surface for the He(S-1) plus NO(X (2)Pi) interaction and bound rovibrational states, J CHEM PHYS, 112(5), 2000, pp. 2195-2203
Adiabatic potential-energy surfaces for the (2)A' and (2)A " states of the
He(S-1)-NO(X (2)Pi) complex have been calculated at the restricted coupled
cluster level of theory including single, double, and noniterated triple ex
citations [RCCSD(T)]. The potential-energy surface (PES) of the A' state ha
s three minima: for the T-shaped geometry, barely skewed toward oxygen (R=6
.07 a(0), Theta=96.7 degrees, and D(e)approximate to 29.2 cm(-1)), and for
two collinear forms. In contrast, PES of the A " state has two minima, both
related to T-shaped forms: (i) A global minimum, with He shifted toward ni
trogen (R=6.27 a(0), Theta=76.1 degrees, and D(e)approximate to 25.3 cm(-1)
), and a shoulderlike minimum, with He shifted toward oxygen (R=6.34 a(0),
Theta=117.6 degrees, and D(e)approximate to 24.5 cm(-1)). The collinear for
ms of the A " state correspond to saddle points. The A' surface lies above
the A " surface, except in the vicinity of perpendicular arrangement. The i
nteraction energies have been analyzed via perturbation theory of intermole
cular forces. The shape and location of the minima is determined primarily
by the anisotropy of the exchange component, and stronger repulsion of A' i
s due to repulsion between the singly occupied anti-bonding pi* orbital and
He. A variational calculation of the bound rovibrational states supported
by the potential suggests that the HeNO complex is bound by about 7 cm(-1).
The bound levels correlate with NO rotational levels with j=1/2 and j=3/2,
and are well described as nearly free-rotor states in which j (NO rotation
) and L (end-over-end rotation of R) are nearly good quantum numbers. Excit
ed intermolecular stretching vibrations are not predicted to be bound. (C)
2000 American Institute of Physics. [S0021-9606(00)30404-4].