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A global nine-dimensional potential energy surface (GPES) for the adiabatic ground state of the H[SUB5] system which fits the ab initio data, reported in the previous paper of this series, has been obtained (root-mean-square error 2.2 kcal/mol). The global fitting procedure is an extension of the corresponding procedure for triatomic and tetra-atomic systems including the functional form previously proposed by the authors. The H[SUB5] GPES obtained here is totally symmetric with respect to permutations of the hydrogen atoms and satisfies the criteria needed to be used in scattering calculations. [ABSTRACT FROM AUTHOR]

The ground-state adiabatic potential energy surface was computed for 2836 conformations of H[SUB5], using a multiple reference single and double excitation configuration interaction program and an extended basis set. The transition state obtained is that of a pentagon with D[SUB5h] symmetry. We find the energy barrier to lie at 81 kcal/mol within ±1 kcal/mol if a multireference Davidson's correction is employed, while the D[SUBe](H[SUB2]) at this level was 109 kcal/mol. The calculations presented here clearly show the energy of H[SUB5] in D[SUB5h] symmetry to be 28 kcal/mol below the dissociation energy of H[SUB2], and therefore a bimolecular mechanism, in the presence of hydrogen atoms, could indeed be considered for the exchange process: H[SUB2]+D[SUB2]+H→2HD+H. [ABSTRACT FROM AUTHOR]

The adiabatic global potential energy surface of the H[sub 3][sup +] system for the lowest triplet excited state of A[sup ′] symmetry was computed for an extensive grid of conformations around the minimum region at full configuration interaction ab initio level, using a much more extended basis set than in a previous paper from the same authors. An accurate global fit (rms error lower than 27 cm[sup -1] for energies lower than dissociation into separated atoms and lower than 5 cm[sup -1] for energies lower than the dissociation channel) to these ab initio points and also to part of the previous calculated points (for a total of 7689 energies in the data set) of the lowest triplet excited state of A[sup ′] symmetry is obtained using a diatomics-in-molecules approach corrected by one symmetrized three-body term with a total of 109 linear parameters and 1 nonlinear parameter. This produces an accurate global potential which represents all aspects of the bound triplet excited state of H[sub 3][sup +] including the minima and dissociation limits, satisfying the correct symmetry properties of the system. The vibrational eigenstates have been calculated using hyperspherical coordinates with symmetry adapted basis functions with the proper regular behavior at the Eckart singularities. The accuracy of the vibrational levels thus obtained is expected to be better than 2 cm[sup -1] with respect to unknown experimental values. Due to the presence of three equivalent minima at collinear geometries (D[sub ∞h]) the lower vibrational levels are close to triple degenerate. Since the interconversion barrier between the three minima is about 2640 cm[sup -1], these states split for the upper excited vibrational levels. Such splitting can provide a key feature to identifying the unassigned transitions amongst the many H[sub 3][sup +] lines that have been observed in hydrogen plasmas. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Adiabatic global potential energy surfaces, for singlet and triplet states of A[sup ′] and A[sup ″] symmetries, were computed for an extensive grid for a total of 8469 conformations of H[sub 3][sup +] system at full configuration interaction ab initio level and using an extended basis set that has also been optimized for excited states. An accurate (root-mean-square error lower than 20 cm[sup -1]) global fit to the ground-state potential is obtained using a diatomics-in-molecules approach corrected by several symmetrized three-body terms with a total of 96 linear parameters and 3 nonlinear parameters. This produces an accurate global potential which represents all aspects of ground-state H[sub 3][sup +] including the absolute minimum, the avoided crossing and dissociation limits, satisfying the correct symmetry properties of the system. The rovibrational eigenstates have been calculated up to total angular momentum J=20 using hyperspherical coordinates with symmetry adapted basis functions. The infrared spectra thus reproduced is within 1 cm[sup -1] with respect to the experimental values for several transitions. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]