On the H+F2→HF+F reaction. An ab initio potential energy surface

Abstract

Rigorous quantum mechanical calculations have been carried out to predict the $\mathrm{H}+{\mathrm{F}}_2\to \mathrm{HF}+\mathrm{F}$ potential energy surface. A double zeta basis set was used, and open‐shell self‐consistent‐field (SCF) calculations were carried out. In addition, electron correlation was explicitly treated using first‐order wavefunctions, made up of 555 ²A′ configurations. Orbitals were optimized by the interative natural orbital method. From the SCF calculations the barrier height and exothermicity are predicted to be 12.2 and 132.4 kcal/mole, respectively. The configuration interaction (CI) values are 1.0 and 88.3 kcal, in much better agreement with the experimental values, 1.2 and 102.5 kcal. The saddle point is predicted from the CI calculations to occur for a linear geometry, $\mathrm{R(}\mathrm{H–F}\text{)=2.05\hspace{0.17em}Å, R(}\mathrm{F–F}\text{)=1.57\hspace{0.17em}Å}$ . This corresponds to an H–F separation more than twice as great as in the HF molecule but an F–F separation is only slightly (0.03 Å) longer than in the isolated F₂ molecule. A substantial number of calculations were carried out for nonlinear HF₂ to determine the anisotropy of the surface. Finally, a brief description is given of electronic structure changes during the reaction.