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

Abstract

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.