RETARDATION LONG-RANGE POTENTIALS BETWEEN 2 HELIUM-ATOMS

The retardation long-range potentials between two 1 S-1 (or 2 S-3) hel ium atoms are calculated. The complex dynamic multipole polarizabiliti es of 1 S-1 and 2 S-3 states of helium are obtained through a variatio n-perturbation approach with B-spline and Slater-type basis functions in a configuration-interaction scheme. They are used to calculate the retardation long-range potentials. The retardation coefficients are ex amined. Their relative magnitudes are different for different systems. The possibility of an excited state of helium dimer from the 1 S-1-2 S-3 He-2 state is estimated.