Hyperfine Interactions in Molecular Iodine

Abstract

The hyperfine structure of eleven optical transitions in the molecules ${\mathrm{I}}_2^{127}$ and ${\mathrm{I}}_2^{129}$ was resolved by the technique of laser-saturated absorption. All the absorption lines correspond to transitions between the ${}_{}{}^1{}_{}{}^{}\Sigma _g^{+}{}_{}{}^{}\mathrm{}\left(X\right)\mathrm{}$ and the ${}_{}{}^3{}_{}{}^{}\Pi _{0u}^{+}{}_{}{}^{}\mathrm{}\left(B\right)\mathrm{}$ electronic states, but the rotational and vibrational quantum numbers varied widely. Two distinct types of hyperfine interaction were observed: (i) a nuclear electric quadrupole coupling which changed little among the lines investigated, and (ii) a magnetic spin-rotation interaction which varied strongly with the vibrational energy in the electronically excited state. The origin of the latter effect is discussed.