Improved calculations of the lowest vibrational transitions in HeH+

Abstract

More accurate variational calculations of the lowest three pure vibrational states v=0,1,2 of the 4HeH+ molecular ion have been carried out without assuming the Born-Oppenheimer approximation. In the calculations we included the complete set of 2 relativistic corrections, i.e., mass-velocity, Darwin, spin-spin, and orbit-orbit. This allowed us to improve the agreement between the theory and the experiment for the vibrational frequencies of the 1→0 and 2→1 transitions as compared to our previous calculations