EMISSION SPECTRUM OF $I_{2}$: ION-PAIR STATES NEAR $47,000 CM^{-1*}$

Author Institution: Department of Chemistry, Vandervilt UniversityIn the emission spectrum of $I_{2}$ in Ar, the second most intense band is a narrow peak near 2880 \AA accompanied by several progressively weaker shoulders and peaks extending to 2830 \AA . $^{1}$At low resolution this system strongly resembles the bound-free $B\rightarrow X$ and $D\rightarrow X$ emission bands of the rare gas $halides.^{2}$ Under high resolution and the use or a ``cool"" discharge, this system displays fine violet-degraded band structure. The analysis of the vibrational structure indicates that the transition originates from an ion-pair excited state and terminates on weakly bound lower state which dissociates to two ground-state atoms. By a process of elimination we arrive at the probable designation. $O_{g}^{-}(^{3}P_{1}) \rightarrow 2431 O_{u}^{-}(^{3}\Pi)$. According to this Interpretation the upper state is the fourth or six predicted ion-pair states near $47,000 cm^{-1}$ to be identified experimentally, and the lower state is that last case c component of the lowest $^{3}\pi$ state to be observed. $^{*}$ Work supported by the Air Force Office of Scientific Research. $^{1}$ A. L. Guy, et al., Chen. Phys. Lett. 73. 582 (1980). $^{2}$ J. Tellinghuisen, et al., J. Chen, Phys. 65. 4473 (1976