Spectroscopic studies of lasing transitions in the diatomic mercury halides

The B doublet Sigma(+) goes to X doublet Sigma(+) emission spectra of HgCl, HgBr, and HgI have been photographed and analyzed for the single isotopic species, Hg200 Cl35, Hg200Br79, Hg200I121 and Hg200I129. In every case the vibrational analysis corroborates Wieland's earlier work (1960) qualitatively but not quantitatively, in that the assignments deviate from his for high v' levels, leading to lower estimates of the dissociation energies of the ground states. In addition, the isotope effect for HgI indicates that Wieland's v' numbering should be decreased by one unit. Trial-and-error Franck-Condon calculations yield the following values for Delta R sub e (= R sub e' - R sub e') 0.60A(HgCl), 0.57A(HgBr), and 0.49A(HgI). These values are somewhat larger than reported previously, and they lead to significant changes in the Franck-Condon distributions for HgCl and HgBr. The reported laser ''lines'' in all three molecules occur in the region of strongest spontaneous emission. However, it seems that most of the laser features cannot be assigned to specific v'-v' bands. Rather, they appear to occur on a quasicontinuum of densely overlapped rotational lines of several v'-v'' bands in the various isotopic HgX molecules present in ''natural'' HgX.