Argon Matrix Infrared Spectrum of the ClO Radical

The matrix reaction of dichlorine monoxide with alkali metal atoms at high dilution in argon produces absorptions due to the appropriate alkali metal chlorides and bands near 995 and 850 cm⁻¹ which show the calculated oxygen isotopic shift for a ClO diatomic species and are independent of the alkali metal used to generate the reaction. The 995‐cm⁻¹ feature has an appropriate chlorine isotopic counterpart for ClO. Experiments altering the concentrations of Cl₂O and lithium atom reactants identify the 995‐cm⁻¹ absorption as the vibrational fundamental of ClO and the 850‐cm⁻¹ band as ClO perturbed by another molecule, perhaps the Cl₂O precursor. This assignment is consistent with the conclusions of earlier matrix isolation studies of ClO species. The high Cl–O force constant in the chlorine oxide free radical is rationalized in terms of $\mathrm{(p–p)\hspace{0.17em}\pi }$ bonding.