Perturbation theory of the spatial confinement effects in the Rydberg HeH molecule

The applicability of the perturbation theory to studies on the effect of confinement is discussed in the context of the influence of spatial confinement on the Rydberg HeH molecule. In the analysis the confining potential is assumed to have cylindrical symmetry, with symmetry axis of the potential overlapping with the molecular axis. In the direction perpendicular to the axis the quadratic dependence of the potential on the electron coordinates is assumed. The ionization due to the confinement and the influence of the confining potential on the form of the potential energy curves, in particular on the bond lengths, are studied in detail.