Initio investigation of XCH2CH2 and XCHCH3 radicals (X = F, Cl, Br)

We have done ab initio calculations to find the equilibrium geometries, rotational/inversion barriers, and harmonic vibrational frequencies of several haloethyl radicals (XCH2CH2 and XCHCH3 where X = F, Cl, Br). One equilibrium and two transition conformations for XCH2CH2 (X = Cl, Br) and XCHCH3 (X = F, Cl, Br) were found on the calculated B3LYP/6-311++G(3df,3pd) potential energy surface. We discuss the effects of the halo substituents on the haloethyl radicals investigated, The C-X bends of the equilibrium beta-haloethyl radicals weaken due to hyperconjugative interaction enhancement as X goes from F to Br. The rotational barriers about the C-C bond have been located using analytical methods. We have also made preliminary vibrational assignments of two bromoethyl radical conformers to experimental transient resonance Raman spectra obtained from the A-band photodissociation of 1-bromo-2-iodoethane.