Accurate non-Born-Oppenheimer calculations of the lowest vibrational energies of D2 and T2 with including relativistic corrections

► New estimate of the fundamental vibrational transition in D2 molecule based on available experimental data is 2993.6108(30) cm-1. ► The inclusion of the relativistic corrections to the transition energy of D2 worsens the agreement between the theory and experiment. ► 0→1 vibrational transitions in D2 and T2 calculated with the inclusion of the relativistic corrections overestimate the experiment by about 0.01-0.02 cm-1. ► α3 QED corrections need to be included in calculations in order to improve the theoretical estimates of the vibrational frequencies.