Electronic Absorption Spectra of the Gaseous 3d Transition-Metal Dichlorides

Electronic absorption spectra of gaseous VCl2, CrCl2, FeCl2, CoCl2, NiCl2, and CuCl2 have been measured near 1000°C and in the range 4000–50 000 cm−1. With the exception of VCl2, extensive vibronic structure was observed in the spectra of these molecules. The spectra are characterized by low intensity (ε=10–120 liter/mole·cm) dn←dn transitions in the 4000–22 000-cm−1 region and by higher intensity (ε=2500–24 000 liter/mole·cm), transitions in the 19 000–50 000-cm−1 region. The dn←dn transitions are reasonably well fitted by A2=±900 cm−1, A4=±100 cm−1, the two ligand-field parameters appropriate for a molecule of symmetry D∞h. The narrow band (half-width ∼120 cm−1) at 11 727 cm−1 in NiCl2 is assigned to a 1Σ(1D)←3π(3F) transition.