EFFECTIVE REDUCED MASS FOR THE INTERACTION OF 2 GROUND-STATE HYDROGEN-ATOMS IN A NONADIABATIC HEITLER-LONDON APPROXIMATION

The relative motion of two ground state hydrogen atoms is considered i n the framework of the resonating group method and using the Heitler-L ondon electronic basis. It is shown that, with correct simultaneous ac count for boundary conditions and indistinguishability of electrons, t he effective reduced mass involved in the relative motion of atoms may be written as 1/2 (M + 1 + delta M) where Mis the proton mass in atom ic units. The correction delta M, which is obtained as a function of t he internuclear distance R, is different in sign and amplitude for the singlet and triplet states, it is of the order of unity at R = 3 au a nd goes exponentially to zero as R increases.