1. The half‐life of an isolated 1s2s3S helium atom may be as long as 109 sec: G. W. F. Drake and A. Dalgarno, Astrophys. J. 152, L121 (1968).ASJOAB0004-637X
2. (a) C. R. Jones and W. W. Robertson, 20th Annual Gaseous Electronics Conference, San Francisco, Calif., 1967 (unpublished).
3. (b) K. H. Ludlum, L. P. Parson, and J. M. Caffery, Jr., J. Chem. Phys. 46, 127 (1967). JCPSA60021-9606
4. (c) E. H. S. Burhop, Proc. Phys. Soc. (London) A67, 276 (1954).PPSAAM0370-1298
5. (a) F. A. Matsen and D. R. Scott, Quantum Theory of Atoms, Molecules, and the Solid State, P.‐O. Löwdin, Ed. (Academic Press Inc., New York, 1966), p. 133.