Matrix-Isolation Study of the Infrared and Ultraviolet Spectra of Several First-Series Transition-Metal Dichlorides

Abstract

Individual molecules of CrCl₂, MnCl₂, FeCl₂, CoCl₂, and NiCl₂ have been isolated in an argon matrix at 14°K in sufficient concentration for infrared and ultraviolet spectroscopic study not only by using the conventional effusion cell as a source of the MCl₂ species, but also by trapping the products of the reaction of chlorine with the hot transition‐metal surface. Studies of the infrared spectra of all of these species in the 250–5500‐Å spectral range are consistent with a linear structure. Ultraviolet absorptions in the 2000–5500‐Å spectral range are in good agreement with the previously reported gas‐phase absorptions. However, the absorption observed for matrix‐isolated NiCl₂ between 4400 and 5000 Å must be attributed to three different electronic transitions, one of which exhibits extensive band structure. A molecular‐orbital treatment involving participation of the $\text{3d}$ nickel electrons in the bonding of the molecule predicts the occurrence of several transitions in this energy range and provides a framework for understanding the appearance of extensive vibrational structure in several of the electronic transitions of NiCl₂.