An ab initio study of the kinetics of the reactions of halomethanes withthe hydroxyl radical.3.kinetic parameters predictions for the otentialhalonreplacements CH_2FBr CHFBr_2,CHFClbR,cHCl_2Br,and CHCIB_2

摘要

Ab initio PMP4(SDTQ)/6-31 1G(3df,2p)11MP216-3 1 IG(2d,2p) calculations, together with canonical transition state theory, were used in order to compute the energetics and predict the kinetic.s4in4e temperature range 250—400 K) of the H atom abstraction reaction between the hydroxyl radical and the five halomethanes: CH_2FBr, CHFBr_2, CHFCIBr, CHCI2Br, and CHClBr2. The procedure adopted in this study has been discussed and validated in our previous two publications (Louis, F.; Gonzalez, C. A.; Huie, R. E.; Kurylo, M. J. J. Phys. Chem. A 2000, 104, 2931. Louis, F.; Gonzalez, C. A.; Huie, R. E.; Kurylo, M. J. J. Phys. Chem. A 2000, 104, 8773.). In the present work, this computational procedure is extended to develop relations of the Evans—Polanyi type, which provide an alternate method to predict rate constants for other reactions where computational expense becomes a limiting factor. In addition, rate constants computed at 277 K were used in the estimation of the atmospheric lifetimes for the five halomethanes. The validity of these results is also discussed.