Near-infrared spectrum and rotational predissociation dynamics of the He–HF complex from an ab initio symmetry-adapted perturbation theory potential

Abstract

Starting from an ab initio symmetry-adapted perturbation theory potential energy surface we have performed converged variational and close-coupling calculations of the bound rovibrational states and of the positions and widths of rotationally predissociating resonances of HeHF and HeDF van der Waals complexes. The energy levels were used to compute transition frequencies in the near-infrared spectra of these complexes corresponding to the simultaneous excitation of vibration and internal rotation in the HF(DF) subunit in the complex. The computed transition energies and other model independent characteristics of the near-infrared spectra are in excellent agreement with the results of high-resolution measurements of Lovejoy and Nesbitt [C. M. Lovejoy and D. J. Nesbitt, J. Chem. Phys. 93, 5387 (1990)]. In particular, the ab initio potential predicts dissociation energies of 7.38 and 7.50 cm " ' for HeHF and HeDF, respectively, in very good agreement with the Lovejoy and Nesbitt results of 7.35 and 7.52 cm -1. The agreement of the observed and calculated linewidths is less satisfactory. We have found, however, that the linewidths are very sensitive to the accuracy of the short-range contribution to the Vj(r,/?) term in the anisotropic expansion of the potential. By simple scaling of the latter component we have obtained linewidths in very good agreement with the experimental results. We have also found that this scaling introduces a very small (2%) change in the total potential around the van der Waals minimum.

Bound states and scattering resonances of OH(A)–He

“…Similar results have been reported for the scattering resonances of He-HF ͑j =1͒. 19,20 Formally the resonances associated with OH͑A͒, n = 2 belong to manifolds with K = 0, 1, and 2. However, rotation of the complex mixes states that differ in K via Coriolis coupling.…”

“…This splitting is primarily determined by vibrationally averaged value of the V 2 potential parameter. 17,20 The discrepancy indicates that the ab initio calculations overestimate the contribution of V 2 by about 10% over the range of radial separations sampled by the zero-point motion. For the n = 2 group the discrepancy in the separations of the N = 2 resonances is more difficult to interpret.…”

Accurate computations of the rovibrational spectrum of the He–HF van der Waals complex

“…This method was used together with Hutson's potential surface [9c] to obtain the rovibrational energy levels for He-HF, among other complexes. These energy levels were close to those obtained by Lovejoy et al [14] Moszynski et al [18,19] used symmetry-adapted perturbation theory (SAPT) and medium size basis sets to compute the intermolecular potential energy surfaces and the rovibrational spectra of the HeHF and HeDF complexes. The calculations were performed for three different HF distances, 1.6078, 1.7328 and 1.9180 a 0 .…”

Bound state spectroscopy of NH–He

“…This is similar to the situation encountered for He-HF. 9,10 Assignment of the observed spectral features was performed by searching for ground state combination differences that were compatible with the theoretical estimate for the rotational constant. The complex band assignments indicated in Fig.…”