Quantum scattering calculations on the S(N)2 reaction Cl-+CH3Br -> ClCH3+Br-

The gas-phase S(N)2 reaction Cl-+CH3Br(v,k)-->ClCH3(v'k')+Br- has been stud ied using reduced dimensionality time independent quantum scattering theory . The C-Br and C-Cl stretching degrees of freedom (quantum numbers v and v' ) and the azimuthal angle (rotation of the CH3 group; quantum numbers k and k') are treated explicitly. An infinite order sudden approximation and Rad au coordinates for the stretching modes are used. The scattering problem is formulated in hyperspherical coordinates. A potential energy surface of Wa ng, Zhu, and Hase is used. It is found that this surface can reproduce the experimentally observed independence of the rate constant on the internal t emperature of CH3Br only if it is scaled to enable the transition state geo metry to agree with high level ab initio data. The reaction cross sections show the propensity rule Delta k=0 for the azimuthal rotation. (C) 1999 Ame rican Institute of Physics. [S0021-9606(99)01719-5].