Using a published correlated wave function computed by Poshusta and Matsen, we have obtained a vibrationally averaged first-order spin-spin constant of -0.04089 ${\mathrm{cm}}^{-1\mathrm{}}$ for the $a {}_{}{}^3{}_{}{}^{}\Sigma _u^{+}{}_{}{}^{}$ metastable state of molecular helium. This is in good agreement with the experimental value of -0.0367 ${\mathrm{cm}}^{-1\mathrm{}}$ recently reported by Lichten et al. Our results strongly suggest that second-order spin-orbit effects are small.

• Received 28 May 1974

DOI:https://doi.org/10.1103/PhysRevA.10.1522