Nonadiabatic couplings in low-energy collisions of hydrogen ground-state atoms

The effect of nonadiabatic couplings on low-energy s-wave scattering of two hydrogen atoms is investigated. Coupling matrix elements are computed in a wide range of internuclear distances. The resulting scattering equations are numerically unstable and therefore are integrated only approximately. Computations are performed for H, D, and T atoms. The phase shifts in the zero velocity limit are inversely proportional to the nuclear reduced mass ${\delta }_0\approx 0.392/\mu .$ This leads to infinite scattering lengths.