Spectroscopy of the H⋯H+ and D⋯D+ charge/induced-dipole complexes

Abstract

The first excited electronic state of the hydrogen molecular ion is essentially repulsive, but exhibits a shallow potential well with a minimum at 6.64 Å because of the long-range H⋯H⁺ charge/induced-dipole interaction. This well supports a small number of stable vibration–rotation levels, and we have observed an infrared electronic spectrum of the D⁺₂ ion arising from transitions to the D⋯D⁺ levels from high-lying vibration–rotation levels of the ground state. We have also detected two microwave electronic transitions in D⁺₂ and one in H⁺₂, thereby confirming the existence of these long-range states. This paper describes the principles, experimental techniques and interpretation of these studies.