Matrix Infrared Spectra and Density Functional Calculations of CH2Cl-Cl and CH2Br-Br Produced by Laser-ablated Metal Plume Irradiation

摘要

CH2Cl-Cl and CH2Br-Br, photoisomers of CH2Cl2 and CH2Br2 , were identified in the matrix IR spectra from the precursors exposed to plume radiation of a laser-ablated transition metal. On the other hand, the corresponding photoisomers of CH2F2 and CH2FCl (CH2F-F, CH2F-Cl, and CH2Cl-F) were not observed because of their instabilities. The CX bond of the product is unusually strong, leading to a high CX stretching frequency. Natural bond orbital (NBO) analysis reveals that it is a true carbon-halogen double bond; in contrast, the XX bond is largely ionic (H2C-X delta+...X delta-), similar to the previously studied analogs from tri- and tetrahalomethanes. Intrinsic reaction coordinate (IRC) computation reproduces the smooth interconversion between the precursor and the energetically higher photoisomer, consistent with the disappearance of the product during visible photolysis.