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

Abstract

The rovibrational spectrum of the He–HF van der Waals complex is calculated from an accurate intermolecular potential energy surface. This is obtained by fitting a considerable number of interaction energies evaluated at the Coupled Cluster Singles and Doubles level including connected triple corrections and with an augmented correlation consistent polarized valence quintuple zeta basis set extended with a set of 3s3p2d1f1g mid-bond functions. The basis set was selected after a systematic study carried out at four intermolecular geometries. The potential is characterized by two linear minima, i.e., He–HF and He–FH, with distances from the He atom to the HF centre of mass of 3.1662 Å and 2.9989 Å and binding energies of −43.844 and −26.169 cm⁻¹, respectively. These results are compared to data available in the literature. An analytic fit to this potential energy surface is presented and used to compute several low-lying rovibrational energy states using coupled channel methods. These results are compared with fixed-frame diffusion Monte-Carlo calculations using a method developed specifically for linear molecules.

Keywords:

• Rovibrational spectrum
• CCSD(T) intermolecular potential energy surface
• He–HF van der Waals complex

Acknowledgements

This work has been supported by the European Research and Training Network NANOQUANT, contract No. MRTN-CT-2003-506842; by the Spanish Ministerio de Educación y Ciencia and FEDER (CTQ2005-01076 project); by the Petroleum Research fund, administered by the American Chemical Society; and by the US National Science Foundation though grant 0202185. We acknowledge computer time from CESGA.