Nonadiabatic Relativistic Correction to the Dissociation Energy of H2, D2, and HD

The relativistic correction to the dissociation energy of H2, D2, and HD molecules has been accurately calculated without expansion in the small electron-nucleus mass ratio. The obtained results indicate the significance of nonadiabatic effects and resolve the discrepancy of theoretical predictions with recent experimental values for H2 and D2. While the theoretical accuracy is now significantly improved and is higher than the experimental one, we observe about 3σ discrepancy for the dissociation energy of HD, which requires further investigation.</p>