Anisotropy effects in methyl chloride ionization by metastable neon atoms at thermal energies

Quasiclassical trajectory calculations have been carried out for the Pennin g ionization reaction Ne*(P-3(2,0)) + CH3Cl --> CH3Cl+(X, A, B) + Ne + e(-) . The calculations have been performed, within the rigid rotor approximatio n, for the translational energy range of 0.04-0.2 eV. The interaction poten tial of the colliding Ne*-CH3Cl system has been semiempirically estimated. The ionization probability has been determined, within the assumption that ionization occurs at the turning point, using a model which takes into acco unt both geometry of the intermediate complex and ab initio electron densit y distribution of the orbitals involved on ionization. Calculations carried out for different rotational states (j = 0, 7, 14, 21, and 28, being j = 1 4 the most populated rotational level at 300 K) manifest the influence of C H3Cl rotation on partial (that is for specific X, A, B electronic states of CH3Cl+) and total ionization. Results averaged for the populated rotationa l levels at 300 K show that total ionization cross section decreases with t ranslational energy. The branching ratio to X and A states also decreases, while that to the B state increases. These results fairly reproduce previou s experimental results on the energy dependence total ionization cross sect ion and branching ratios for the production of CH3Cl+, CH2Cl+, and CH3+ ion s.