A rigid rotor in a tetrahedral field model was applied to (H,Be) and (D,Be) complexes. The issue of <111>, as opposed to <100>, minima was explored; with the latter model providing support for these complexes. It was then shown that parity was nearly a good quantum number for the wave functions when the minima were in <100> directions; even though the Hamiltonian was invariant under operations of the group, Td. Calculations were then made of stress effects upon the levels within this model; thus refuting the suggestion that a [111] stress had no effect when the minima were in six <100> directions. The stress effects for the small basis-set tetrahedral tunnelling model were re-calculated, and it was found that previous conclusions would have to be re-evaluated. Formulae were also presented for stress effects in the small basis-set octahedral tunnelling model. A coupling scheme was developed by using symmetry arguments, and oscillator strengths were calculated for transitions in both the infra-red (hole transition plus rotational side-bands) and far-infrared (coupled rotational transitions).

K.R.Martin, W.B.Fowler: Physical Review B, 1995, 52[23], 16516-29