Molecular structure in non-Born–Oppenheimer quantum mechanics

We present the first fully non-Born–Oppenheimer (BO) calculations of the wave function of a molecule with more than two atoms: H3+ and its isotopomers. We also calculate expectation values of the internuclear distances (i.e., the molecular geometry). Since the operators representing the internuclear distances do not commute with the internal non-BO Hamiltonian, the only information that can be acquired from the wave function are the average values of bond distances and for each subset of identical nuclei in the system only one unique interparticle distance can be determined.