Fundamental vibrational transitions of the 3He 4He+ and 7LiH+ ions calculated without assuming the Born-Oppenheimer approximation and with including leading relativistic corrections

Abstract

Very accurate variational calculations of the fundamental pure vibrational transitions of the 3He 4He+ and 7LiH+ ions are performed within the framework that does not assume the Born-Oppenheimer BO approximation. The non-BO wave functions expanded in terms of one-center explicitly correlated Gaussian functions multiplied by even powers of the internuclear distance are used to calculate the leading relativistic corrections. Up to 10 000 Gaussian functions are used for each state. It is shown that the experimental 3He 4He+ fundamental transitions is reproduced within 0.06 cm−1 by the calculations. A similar precision is expected for the calculated, but still unmeasured, fundamental transition of 7LiH+. Thus, three-electron diatomic systems are calculated with a similar accuracy as two-electron systems