A calculation of the interaction potential and hyperfine shift in HeH

The interatomic potential V(R) and hyperfine splitting constant a(R) for a hydrogen atom in interaction with a helium atom are calculated as functions of the internuclear distance R(3<or=R<or=12a0) by a generalized valence bond procedure. Using these configurations, a separate perturbation calculation of the coefficients of the leading (R-6) terms in the asymptotic expansion of V(R) and a(R) yields values in good agreement with previous estimates. Comparison with previous calculations of V(R) indicates that further investigation is required to establish accurate values in the vicinity of the potential minimum. The function a(R) is also found to exhibit a shallow minimum, and it is emphasized that calculations of a(R) can be inaccurate if the decision on which terms to include in the wavefunction is based on energetic considerations alone. The computed hyperfine shift at 50 degrees C is 10% smaller than the most recent experimental value, the agreement becoming closer with increasing temperature. Values obtained for the temperature derivative of the shift are consistent with the available experimental data.