Theoretical study for the reaction of CH3OCl with Cl atom

A direct dynamics method is employed to study the kinetics of the multiple channel reaction CH3OCl + Cl. The potential energy surface (PES) information is explored from ab initio calculations. Two reaction channels, Cl‐ and H‐abstractions, have been identified. The optimized geometries and frequencies of the stationary points and the minimum‐energy paths (MEPs) are calculated at the MP2 level of theory using the 6‐311G(d, p) and cc‐pVTZ basis sets, respectively. The single‐point energies along the MEPs are further refined at the G3(MP2)//MP2/6‐311G(d, p), G3//MP2/6‐311G(d, p), as well as by the multicoefficient correlation method based on QCISD (MC‐QCISD) using the MP2/cc‐pVTZ geometries. The enthalpies of formation for the species CH3OCl and CH2OCl are calculated via isodesmic reactions. The rate constants of the two reaction channels are evaluated by using the variational transition‐state theory over a wide range of temperature, 220–2200 K. The calculated rate constants exhibit the slightly negative temperature dependence and show good agreement with the available experimental data at room temperature at the G3(MP2)//MP2/6‐311G(d, p) level. The present calculations indicate that the two channels are competitive at low temperatures while H‐abstraction plays a more important role with the increase of temperature. The calculated k1a/k1 ratio of 0.5 at 298 K is in general agreement with the experimental one, 0.8 ± 0.2. The high rate constant for CH3OCl + Cl shows that removal by reaction with Cl atom is a potentially important loss process for CH3OCl in the polar stratosphere. © 2005 Wiley Periodicals, Inc. J Comput Chem 26: 642–650, 2005

[1]  B. C. Garrett,et al.  Variational Transition State Theory , 1980 .

[2]  M. W. Chase,et al.  NIST-JANAF Thermochemical Tables Fourth Edition , 1998 .

[3]  Dietmar Heidrich,et al.  The Reaction path in chemistry : current approaches and perspectives , 1995 .

[4]  P. Crutzen,et al.  On the potential importance of the gas phase reaction CH3O2 + ClO → ClOO + CH3O and the heterogeneous reaction HOCl + HCl → H2O + Cl2 in “ozone hole” chemistry , 1992 .

[5]  Donald G. Truhlar,et al.  Generalized transition state theory. Bond energy-bond order method for canonical variational calculations with application to hydrogen atom transfer reactions , 1979 .

[6]  Leo Radom,et al.  Molecular orbital theory of the electronic structure of organic compounds. V. Molecular theory of bond separation , 1970 .

[7]  Donald G. Truhlar,et al.  Statistical thermodynamics of bond torsional modes , 2000 .

[8]  T. A. Wiggins,et al.  Molecular constants of HCl35 , 1965 .

[9]  G. Graner,et al.  Structure of free polyatomic molecules : basic data , 1998 .

[10]  J. A. Coxon,et al.  The visible band absorption spectrum of chlorine , 1970 .

[11]  Wing Tsang,et al.  Heats of Formation of Organic Free Radicals by Kinetic Methods , 1996 .

[12]  A. Colussi,et al.  Quantitative Structure−Stability Relationships for Oxides and Peroxides of Potential Atmospheric Significance , 1996 .

[13]  Donald G. Truhlar,et al.  Criterion of minimum state density in the transition state theory of bimolecular reactions , 1979 .

[14]  Donald G. Truhlar,et al.  Molecular modeling of the kinetic isotope effect for the [1,5]-sigmatropic rearrangement of cis-1,3-pentadiene , 1993 .

[15]  J. Lennard-jones,et al.  Molecular Spectra and Molecular Structure , 1929, Nature.

[16]  Krishnan Raghavachari,et al.  Gaussian-3 theory using reduced Mo/ller-Plesset order , 1999 .

[17]  Donald G. Truhlar,et al.  POLYRATE 4: A new version of a computer program for the calculation of chemical reaction rates for polyatomics , 1992 .

[18]  M. J. Elrod,et al.  A theoretical study of ROX (R=H, CH3; X=F, Cl, Br) enthalpies of formation, ionization potentials and fluoride affinities , 1999 .

[19]  Donald G. Truhlar,et al.  Direct Dynamics Method for the Calculation of Reaction Rates , 1995 .

[20]  Donald G. Truhlar,et al.  A simple approximation for the vibrational partition function of a hindered internal rotation , 1991 .

[21]  Rate Constant and Mechanism of the Reaction between Cl and CH3OCl at 295 K , 1996 .

[22]  J. Farman,et al.  Large losses of total ozone in Antarctica reveal seasonal ClOx/NOx interaction , 1985, Nature.

[23]  G. Herzberg.  Molecular Spectra and Molecular Structure IV. Constants of Diatomic Molecules , 1939 .

[24]  J. S. Francisco.  AN AB INITIO STUDY OF THE STRUCTURES AND ENERGETICS OF CH3OCL AND CH3CLO , 1999 .

[25]  D. Toohey,et al.  Free Radicals Within the Antarctic Vortex: The Role of CFCs in Antarctic Ozone Loss , 1991, Science.

[26]  R. N. Schindler,et al.  Mechanism and rate constants for the reactions of Cl atoms with HOCl, CH3OCl and tert‐C4H9OCl , 1997 .

[27]  Donald G. Truhlar,et al.  Factors Affecting Competitive Ion−Molecule Reactions: ClO- + C2H5Cl and C2D5Cl via E2 and SN2 Channels , 1996 .

[28]  D. C. Clary,et al.  The Theory of Chemical Reaction Dynamics , 1986 .

[29]  Donald G. Truhlar,et al.  Improved treatment of threshold contributions in variational transition-state theory , 1980 .

[30]  L. Curtiss,et al.  Gaussian-3 (G3) theory for molecules containing first and second-row atoms , 1998 .

[31]  D. Truhlar,et al.  MULTI-COEFFICIENT CORRELATION METHOD FOR QUANTUM CHEMISTRY , 1999 .

[32]  S. Butcher,et al.  Microwave Spectrum of Methyl Hypochlorite , 1964 .

[33]  K. Kuchitsu,et al.  Structure of Free Polyatomic Molecules , 1998 .

[34]  I. D. Liu,et al.  RECOMMENDED VALUES FOR THE THERMODYNAMIC PROPERTIES OF HYDROGEN AND DEUTERIUM PEROXIDES , 1955 .

[35]  S. Solomon.  Progress towards a quantitative understanding of Antarctic ozone depletion , 1990, Nature.

[36]  Dong-ming Chen,et al.  The potential energy surface for the decomposition of CH3OCl , 2000 .

[37]  B. C. Garrett,et al.  Current status of transition-state theory , 1983 .

[38]  Donald G. Truhlar,et al.  MC-QCISD: Multi-coefficient correlation method based on quadratic configuration interaction with single and double excitations , 2000 .

[39]  Theoretical C–H bond dissociation enthalpies for CH3OCl and CH3OBr , 2000 .