Gas-phase reaction between calcium monocation and fluoromethane: Analysis of the potential energy hypersurface and kinetics calculations

The gas-phase reaction between calcium monocation and fluoromethane: Ca++CH3F -> CaF+ +CH3 was theoretically analyzed. The potential energy hypersurface was explored by using density functional theory methodology with different functionals and Pople's, Dunning's, Ahlrichs', and Stuttgart-Dresden basis sets. Kinetics calculations (energy and total angular momentum resolved microcanonical variational/conventional theory) were accomplished. The theoretically predicted range for the global kinetic rate constant values at 295 K (7.2 x 10(-11)-5.9 x 10(-10) cm(3) molecule(-1) s(-1)) agrees reasonably well with the experimental value at the same temperature [(2.6 +/- 0.8) x 10(-10) cm(3) molecule(-1) s(-1)]. Explicit consideration of a two transition state model, where the formation of a weakly bounded prereactive complex is preceded by an outer transition state (entrance channel) and followed by an inner transition state connecting with a second intermediate that finally leads to products, is mandatory. Experimental observations on the correlation, or lack of correlation, between reaction rate constants and second ionization energies of the metal might well be rationalized in terms of this two transition state model. (C) 2009 American Institute of Physics. [doi:10.1063/1.3247287]