Intermolecular ab initio potential and spectroscopy of the ground state of HeI2 complex revisited

The structure, energetics, and spectroscopy of ground-state HeI(2) molecule are analyzed from first principles. Ab initio methodology at CCSD(T) level of theory was employed, and large basis sets were used to compute the interaction energies. Scalar relativistic effects were accounted for by relativistic effective core potentials for the iodine atoms. Recent experimental investigations of the HeI(2) rovibronic spectra have estimated the ground-state binding energies of 16.6 +/- 0.6 and 16.3 +/- 0.6 cm(-1) for the T-shaped and linear isomers, respectively. Given the extremely small difference between the two conformers, special attention was paid in the choice of basis sets used and the extrapolation schemes employed, as well as the fitting process for its analytical representation. The complete analytical form is provided, and variational fully quantum mechanical calculations were carried out by using the new parametrized surface, to evaluate vibrationally averaged structures and binding energies for the different conformers. The results obtained are in good accord with recent data available from experimental investigations of the He-I(2) rovibronic spectra.