Dioxirane vibrational frequencies: an unsettling relationship between theory and experiment

Abstract

There appears to be a conflict between theory and experiment concerning the vibrational frequencies of dioxirane, a CH₂O₂ isomer. Here we employ sophisticated ab initio quantum mechanical methods with large basis sets to determine geometry, harmonic vibrational frequencies, infrared (IR) intensities and isotopic shifts of dioxirane. At the highest level of theory, the CCSD(T) approach is used together with a cc-VTZ2P+f,d basis set. Best predictions for CO asymmetric and OO stretching (or OCO deformation) harmonic frequencies are 931 (b₂)cm^-1 and 759 (a₂)cm^-1, respectively. The IR intensities of these two peaks are predicted to be 19 km mol^-1 and 1 km mol^-1. An examination of the experimental vibrational frequencies of substituted dioxiranes is also presented. Calculated frequencies, intensities, and isotopic shifts all imply that the two experimental IR features (with their observed intensity ratio of 2⋅8) assigned to CO stretching (839⋅0 cm^-1) and OCO deformation (800.9 cm^-1) frequencies by J. R. Sodeau and L. J. Whyte (1991, J. chem. Soc. Faraday Trans., 87, 3725) should be re-addressed.