So I'm trying to figure out the average energy of diatomic gas molecules via the equipartition theorem at high temperature (such that it's translational , rotational and vibrational modes are activated) and to do that I need to know the degree of freedom. some websites claim it would be 6 , 3d translational motion , 2 rotational axis and 1 vibration along the bond between the atoms. however, some sources state that they are actually one more: the motion/velocity along the bond. so i'm now a bit confused which version is correct. I'm inclined towards the latter as I think only by including that d.o.f. can I fully describe the configuration of the gas molecules. I would think of the original 3 translational d.o.f. as the motion of the centre of mass only, which is why we need one more to describe the motion along the bond.