Ab InitioCalculations on the H2plus;D2equals;2HD Fourhyphen;Center Exchange Reaction. I. Elements of the Reaction Surface

摘要

We present the results ofab initiocalculations on some interesting regions of the reaction surface for the fourhyphen;center exchange reaction H2thinsp;plus;thinsp;D2thinsp;equals;thinsp;2HD. These calculations, which use a minimum basis set of Slater orbitals, indicate that for all geometries appropriate to the transition state of the reaction, a barrier height of at least 148 kcal/mole is present. This is far greater than the energy required to produce free radicals and more than three times the experimental energy of activation, 42 kcal/mole. Considering the sources and magnitudes for errors due to correlation and basis set restrictions, we estimate the barrier height for this exchange reaction to be 132thinsp;plusmn;thinsp;20 kcal/mole exclusive of zerohyphen;point energies. In this paper we discuss the surface as determined by configuration interaction techniques. We find that the most favorable geometries for the exchange reactions are the square, rhombus, and kite configurations. However, all of these states are unstable with respect to H2thinsp;plus;thinsp;2H. In addition we find no evidence of collision complexes for any of the likely transition state geometries. In the following paper we will examine the G1 wavefunctions for this system in order to obtain an understanding of the factors responsible for the shape of the surface.