High-level ab initio calculations of the ground and several excited-state adiabatic potential surfaces of the NaFH system are reported. These calculations were performed by multireference configuration interaction on a large grid of geometries which allowed them to be used for constructing an accurate analytic representation of the NaFH potential surfaces. For the ground and first excited states, using a genetic algorithm, an analytic 2×2 matrix fit was obtained corresponding to a diabatic representation. The off-diagonal coupling was obtained by fitting the energy gap between the surfaces in the region of their avoided crossing, and the diagonal elements were then fit to reproduce the ab initio adiabatic energy at 1530 points. The full fit was used to locate the barrier and the van der Waals well on the ground-state potential surface, the exciplex on the first-excited-state potential surface, and the minimum energy path for the ground-state Na+HF→NaF+H reaction. Additional calculations on the van der Waals and saddle point regions were carried out by a variety of ab initio methods as a check on accuracy. Major topological features of the potential energy surfaces representing higher-than-first excited states were examined.

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Reaction probabilities, cross sections, rate coefficients, frequency factors, and activation energies for hydrogen-atom abstraction from a hydrogen-covered C(111) surface have been computed using quantum wave packet and classical trajectory methods on the empirical hydrocarbon ♯1 potential hypersurface developed by Brenner. Upper bounds for the abstraction rates, activation energies, and frequency factors have been obtained for six different chemisorbed moieties on a C(111) diamond surface using a classical variational transition-state method. For the hydrogen-covered surface, the results of the wave packet/trajectory calculations give k(T)=1.67×1014 exp(−0.46 eV/kbT) cm3/mol s, which is about a factor of 2.9 less than the gas-phase abstraction rate from tertiary carbon atoms at 1200 K. The variational calculations show that the activation energies for hydrogen-atom abstraction vary from 0.0 to 1.063 eV. Some sp2-bonded hydrogen atoms can be removed in a barrierless process if adjacent to a carbon radical. In contrast, abstractions that produce a methylene carbon are associated with much larger activation energies in the range 0.49–0.82 eV. Abstraction from nonradical chemisorbed ethylene structures of the type that might be formed by the chemisorption of acetylene at two lattice sites is a particularly slow process with a 1.063 eV activation energy. Hydrogen abstraction from sp3 carbon atoms have activation energies ∼0.4 eV. The results suggest that phenomenological growth models which assume either an equilibrium distribution between surface hydrogen/H2 or a common abstraction rate for surface hydrogen atoms are unlikely to be accurate.

A new force field (MSXX FF) was developed for barium sulfate (BaSO 4 ) to reproduce the experimental properties of BaSO 4 crystal (density, lattice energy, compressibility, and vibrational spectrum) and to describe properly the interaction between BaSO 4 and water (binding energies and interatomic distances of Ba(H 2 O) 8 2+ and (SO 4 )(H 2 O) 6 2-clusters determined from ab initio quantum mechanics calculations). Using this FF in combination with F3C FF for water, the surface energies for several surfaces of BaSO 4 were examined both in a vacuum and in the presence of an explicit water bath in contact with them. The same level of FF's are also reported for CaSO 4 and SrSO 4 .