The Continuous Absorption Coefficient of the Helium Atom.

In this paper the continuous absorption coefficient of He i beyond the series limits 504.3 A, 2600.7 A, and 3122 A (i.e., transitions from the ground state 1'S and the two metastable states 23S and 2'S to the continuum) are investigated. For the bound states, wave functions derived from the Ritz principle were used, while for the free states Coulomb wave functions with an effective charge of 1 were used. With these wave functions the continuous absorption cross-sections have been derived from the matrix elements not only of the dipole moment but also of the momentum and of the acceleration. The agreement of values derived from the momentum and the dipole moment provides a strong confirmation of the results obtained from them. However, the cross-sections derived from the acceleration are much smaller. This last circumstance is due to the fact that the main contribution to the matrix elements of the accelera- tion come from very near the origin, where an effective charge of 1 is unsuitable. The integratedf-values for the three continua have also been computed. When these f-values for the continua are added to the respective sums for the discrete states evaluated by other authors, we find that the f-sum rule is ap- proximately satisfied. This is an additional check on our calculation