DUAL-LEVEL DIRECT DYNAMICS STUDIES ON THE HYDROGEN ABSTRACTION REACTION OF CF 3 CHFCF 3 (HFC-227ea) WITH Cl ATOM MASOUD ARABIEH and MANSOUR ZAHEDI * Department of Chemistry, Faculty of Sciences Shahid Beheshti University, G.C., Evin, 19839-63113, Tehran, Iran * m-zahedi@sbu.ac.ir Received 19 June 2012 Accepted 25 September 2012 Published 6 February 2013 The hydrogen abstraction reaction of CF 3 CHFCF 3 (HFC-227ea) by Cl atom is studied theor- etically over a temperature range of 502000 K. The reaction path information such as geo- metries, gradients, etc. are initially obtained at the BB1K/6-31þG (d,p) level. In order to improve the energies, high level single point energy (SPE) calculations are carried out at BB1K/ MG3S on BB1K/6-31+G(d,p) geometries. The rate coe±cients are obtained by dual-level direct dynamics approach with the interpolated SPE method at BB1K/MG3S//BB1K/6-31þG(d,p) level. Aforementioned rate coe±cients are calculated based on canonical variational transition state theory (CVT) with small-curvature tunneling (SCT) correction. The results show that for the title reaction, variational e®ect is small while the tunneling e®ects are signi¯cant at low temperature. In order to investigate the reliability of improved BB1K potential energy surface in predicting barrier height of the reaction, di®erent quantum models built such as QCISD(T)/6-311þþG(d,p)//MP2/6-31G(d,p), QCISD(T)/aug-cc-pv-DZ//MP2/6-31G(d,p), and MP4SDQ/aug-cc-pv-DZ//MP2/6-31G(d,p) are applied to calculate the rate coe±cients of the reaction. The results show the rate coe±cients calculated based on MP2 potential energy surface are underestimated as compared to the experimental value. Finally three models are applied to ¯t the calculated rate coe±cients over the temperature range of 502000 K. It is shown that the new four-parameter model provided a better temperature dependence than the other expressions. It is expected that obtained theoretical results can be useful for modeling the kinetics nature of the reaction of HFC-227ea and Cl atom over temperature range where no experimental data is accessible. Keywords: Variational transition state theory; small curvature tunneling; atmospheric chem- istry; hydrogen abstraction. 1. Introduction Chloro°uorocarbons (CFCs) have been extensively used in many industrial and home usages. These compounds are involved in ozone destruction process via transferring from troposphere into stratosphere. 1,2 Because of such depletion e®ect *Corresponding author. Journal of Theoretical and Computational Chemistry Vol. 12, No. 2 (2013) 1250119 (15 pages) # . c World Scienti¯c Publishing Company DOI: 10.1142/S0219633612501192 1250119-1 J. Theor. Comput. Chem. Downloaded from www.worldscientific.com by 199.19.105.156 on 02/08/13. For personal use only.