SCATTERING LENGTHS FOR COLLISIONS OF GROUND-STATE AND METASTABLE STATE HYDROGEN-ATOMS

Scattering lengths for the collisions of ground and metastable state h ydrogen atoms interacting via the B'(1) Sigma(u)(+), EF(1) Sigma(g)(+) , e(3) Sigma(u)(+) and h(3) Sigma(g)(+) molecular potentials are evalu ated from published ab initio Born-Oppenheimer potentials with adiabat ic corrections, matched to multipole expansions at large interatomic s eparations. It is demonstrated that the scattering lengths are very se nsitive to the connections between the ab initio potentials and their asymptotic forms and the need is shown for accurate interatomic potent ial calculations at greater separations than are currently available. The density-dependent shift and broadening of the 1S-2S transition fre quency in atomic hydrogen caused by two-body elastic collisions are pr esented.