STIMULATED EMISSION SPECTROSCOPY OF $I_{2}$: ELECTRONIC TRANSITION MOMENT OF THE B-X SYSTEM BETWEEN 2.4-4.2 {\AA} AND HYPERFINE STRUCTURE OF $X^{I} \Sigma^{+}_{g}, \; v''= 83$

$^{1}$L. Brewer and J. Tellinghutsen, J. Chem. Phys. 56, 3929 (1972).""Author Institution: Departments of Chemistry, Aeronautics and Astronautics Massachusetts Institute of Technology; Departments of Chemistry, Universite Claude Bernard-Lyon IGain measurements of an optically pumped $I_{2}$ laser for various B-X transitions ranging from $v^{\prime}=43\rightarrow v^{\prime\prime}=9-83$ allow determination of the electronic transition moment as a function of R-centroid. Since the gain is measured under conditions of zero light intensity the measurements are free from ambiguities due to absolute intensity, power broadening, and concentration. The electronic transition moment attains a maximum of $\sim 3D^{2}$ near R-centroid = 3.2 {\AA} as predicted by Tellinghuisen and $Brewer^{1}$ and goes to zero at large R. A stabilized single-mode $Ar^{+}$ laser is used to pump an $I_{2}$ laser thus preparing a different single velocity class of molecules for each hyperfine component in the upper laser level $(B^{3}\Pi_{ou}, v^{\prime} =43)$. Monitoring the $I_{2}$ laser output in the $(v^{\prime}=43, v^{\prime\prime}=83)$ band as a function of the $I_{2}$ laser cavity length gives rise to a spectrum with linewidth of the order of the homogeneous width. This spectrum can be deconvoluted to obtain the hyperfine structure of $v^{\prime\prime} = 83$ of $X^{1} \Sigma^{+}_{g}$ of iodine