Ortho–para nuclear-spin isomerization energies for all bound vibrational states of ditritium (T2) from non-Born–Oppenheimer variational calculations performed with explicitly correlated all-particle Gaussian functions

Abstract

Direct variational calculations, where the Born–Oppenheimer (BO) approximation is not assumed, are performed for all 26 bound rovibrational states corresponding to the lowest rotational excitation (i.e. the N=1 states) of the tritium molecule (T2). The non-BO energies are used to determine the ortho–para isomerization energies. All-particle explicitly correlated Gaussian basis functions are employed in the calculations and over 11000 Gaussians independently generated for each state are used. The exponential parameters of the Gaussians are optimized with the aid of analytically calculated energy gradient determined with respect to these parameters. The non-BO wave functions are used to calculate expectation values of the inter-particle distances and the triton–triton correlation functions.