Spectroscopy of H 3 + based on a new high-accuracy global potential energy surface

Abstract

The molecular ion is the simplest polyatomic and poly-electronic molecular system, and its spectrum constitutes an important benchmark for which precise answers can be obtained ab initio from the equations of quantum mechanics. Significant progress in the computation of the ro–vibrational spectrum of is discussed. A new, global potential energy surface (PES) based on ab initio points computed with an average accuracy of 0.01 cm −1 relative to the non-relativistic limit has recently been constructed. An analytical representation of these points is provided, exhibiting a standard deviation of 0.097 cm −1 . Problems with earlier fits are discussed. The new PES is used for the computation of transition frequencies. Recently measured lines at visible wavelengths combined with previously determined infrared ro–vibrational data show that an accuracy of the order of 0.1 cm −1 is achieved by these computations. In order to achieve this degree of accuracy, relativistic, adiabatic and non-adiabatic effects must be properly accounted for. The accuracy of these calculations facilitates the reassignment of some measured lines, further reducing the standard deviation between experiment and theory.