It is shown that the atmospheric oxygen absorption bands can be attributed to a ${}_{}{}^3{}_{}{}^{}S\to {}_{}{}^1{}_{}{}^{}S$ transition from the normal (${}_{}{}^3{}_{}{}^{}S$) to a metastable ${}_{}{}^1{}_{}{}^{}S$ excited state of ${\mathrm{O}}_2$. This accounts for all the strong lines, and explains missing lines, without conflict with existing theory. Certain very weak series such as the $A^{\prime }$ band are, however, not yet explained. Of the three rotational levels for each value of $j_k$ in the ${}_{}{}^3{}_{}{}^{}S$ normal state, the two for which $j=j_k\pm 1$ show only a very small separation, which increases slowly with $j_k$, while the third is separated from the other two by an interval of about 2 wavenumbers which does not change with $j_k$ (cf. Fig. 2 and Table I). The ${}_{}{}^3{}_{}{}^{}S$ and ${}_{}{}^1{}_{}{}^{}S$ states involved in the atmospheric bands may perhaps be attributed both to the same electron configuration, in agreement with a suggestion made in a previous paper. If this is the case, it is likely that a metastable ${}_{}{}^1{}_{}{}^{}D$ state derived from the same configuration also exists, and that infra-red atmospheric bands corresponding to the transition ${}_{}{}^3{}_{}{}^{}S\to {}_{}{}^1{}_{}{}^{}D$ should be found.

• Received 25 August 1928

DOI:https://doi.org/10.1103/PhysRev.32.880