A theoretical study of the cluster vibrations in Cr2O2,Cr2O3, and Cr2O4

We report the results of first principles calculations on the Cr2O2 Cr2O3, and Cr2O4 clusters for which some of the considered configurations were pro posed in the recent infrared spectroscopy experiments (Chertihin, G. V.; Ba re, W. D.; Andrews, L. J. Chem. Phys. 1997, 107, 2798). Both linear and rin g-like isomers are predicted to be equally probable for Cr2O2 while the (Cr 2O2)O isomer is preferred over the chainlike (OCrOCrO) isomer for Cr2O3. Fo r Cr2O4, a clear preference for the O(Cr2O2)O isomer over the (CrO2)(2) iso mer is predicted. Calculations of the vibrational frequencies for the lowes t energy isomers of these clusters yield the stretching mode involving the stronger Cr-O bond to be around 900-1000 cm(-1) and the bending mode involv ing the puckered-ring to be around 550-700 cm(-1). Overall, the calculated normal modes of the cluster vibrations provide a very satisfactory descript ion of the observed IR spectrum of the chromia clusters.