Isotope Effects in the Reactions of Chloroform Isotopologues with Cl, OH, and OD

Abstract

The kinetic isotope effects in the reactions of CHCl(3), CDCl(3), and (13)CHCl(3) with Cl, OH, and OD radicals have been determined in relative rate experiments at 298 +/- 1 K and atmospheric pressure monitored by long path FTIR spectroscopy. The spectra were analyzed using a nonlinear least-squares spectral fitting procedure including line data from the HITRAN database and measured infrared spectra as references. The following relative reaction rates were determined: k(CHCl(3)+Cl)/k(CDCl(3)+Cl) = 3.28 +/- 0.01, k(CHCl(3)+Cl)/k((13)CHCl(3)+Cl) = 1.000 +/- 0.003, k(CHCl(3)+OH)/k(CDCl(3)+OH) = 3.73 +/- 0.02, k(CHCl(3)+OH)/k((13)CHCl(3)+OH) = 1.023 +/- 0.002, k(CHCl(3)+OD)/k(CDCl(3)+OD) = 3.95 +/- 0.03, and k(CHCl(3)+OD)/k((13)CHCl(3)+OD) = 1.032 +/- 0.004. Larger isotope effects in the OH reactions than in the Cl reactions are opposite to the trends for CH(4) and CH(3)Cl reported in the literature. The origin of these differences was investigated using electronic structure calculations performed at the MP2/aug-cc-PVXZ (X = D, T, Q) level of theory and are compared with previously calculated values for the other methane derivatives. The Born-Oppenheimer barrier heights to H abstraction are 12.2 and 17.0 kJ mol(-1) at the CCSD(T)/aug-cc-pVTZ level of theory for OH and Cl, respectively. The reaction rate coefficients of the two elementary vapor phase reactions including the (2)H and (13)C kinetic isotope effects were calculated using improved canonical variational theory with small curvature tunneling (ICVT/SCT) and the results compared with experimental data.