Description:
<jats:title>Abstract</jats:title><jats:p>The long‐range interaction energies for different dissociation products of the HeH<jats:sup>+</jats:sup> molecule have been calculated using the Rayleigh–Schrödinger perturbation theory up to the third order in the energy. The calculations were carried out for the ground state (He(ls<jats:sup>2</jats:sup>) + H<jats:sup>+</jats:sup>), the first excited state (H(ls) + He<jats:sup>+</jats:sup>(ls)) and the second excited state Π(H(2pπ) + He<jats:sup>+</jats:sup>(ls)). The unperturbed states correspond to the dissociation products denoted in parentheses. Assuming the overlap to be zero, expanding the interaction potential in the inverse powers of the internuclear distance <jats:italic>R</jats:italic> and using the familiarly known perturbation‐variational technique, the coefficients of various powers of <jats:italic>R</jats:italic><jats:sup>−1</jats:sup> in the energy expansion were evaluated. They correspond to different multipole‐multipole interactions. The potential energy curves of all three states under consideration were calculated for large values of <jats:italic>R</jats:italic>. Also calculated were the multipole polarizabilities of the hydrogen atom in the is and 2pπ states and of the helium atom in the ground state.</jats:p>