Leading order nonadiabatic corrections to rovibrational levels of H2, D2, and T2

An efficient computational approach to nonadiabatic effects in the hydrogen molecule (H-2, D-2, and T-2) is presented. The electronic wave function is expanded in the James-Coolidge basis set, which enables obtaining a very high accuracy of nonadiabatic potentials. A single point convergence of the potentials with growing size of the basis set reveals a relative accuracy ranging from 10(-8) to 10(-13). An estimated accuracy of the leading nonadiabatic correction to the rovibrational energy levels is of the order of 10(-7) cm(-1). After a significant increase in the accuracy of the Born-Oppenheimer and adiabatic calculations, the nonadiabatic results presented in this report constitute another step towards highly accurate theoretical description of the hydrogen molecule. (C) 2015 AIP Publishing LLC.