Matrix Infrared Spectrum and Bonding in the Monochloromethyl Radical

Simultaneous deposition of CH2ClX (X = F, Cl, Br, I) with atomic lithium (6Li or 7Li) on a CsI window maintained at 15°K produces new infrared absorptions attributable to LiX and the monochloromethyl radical. The identity of the radical is confirmed by comparing the spectra of the reactions of CHDCl2 and CD2Cl2 with lithium and CH2ClBr with sodium. Absorptions assigned to the symmetric C–Cl stretch, the symmetric H–C–H bend, and the out-of-plane hydrogen bend of the monochloromethyl radical are supported by normal coordinate calculations. The high C–Cl force constant (4.09 ± 0.03 mdyn/Å) suggests (p–p)π bonding in CH2Cl. The large positive quartic term in the out-of-plane bending potential function is consistent with a planar radical.