A new accurate and full dimensional potential energy surface of H5+ based on a triatomics-in-molecules analytic functional form

Abstract

In this work a reliable full nine-dimensional potential energy surface for studying the dynamics of H(5)(+) is constructed, which is completely symmetric under any permutation of the nuclei. For this purpose, we develop a triatoms-in-molecules method as an extension of the more common diatoms-in-molecules one, which allows a very accurate description of the asymptotic regions by including correctly the charge-induced dipole and quadrupole interactions. Moreover, this treatment provides a semiquantitative description of all the topological features of the global potential compared with coupled cluster results. In particular, the hop of the proton between two H(2) fragments produces a double well in the potential. This resonant structure involving the five atoms produces a stabilization, lowering the barrier, and the triatoms-in-molecules yields to a barrier significantly higher than the ab initio results. Therefore, to improve the triatomics-in-molecules potential surface, two five-body terms are added, which are fitted to more than 110,000 coupled-cluster ab initio points. The global potential energy surface thus obtained in this work has an overall root mean square error of 0.079 kcal/mol for energies below 27 kcal/mol above the global well. The features of the potential are described and compared with previous available surfaces.

Dynamically biased statistical model for the ortho/para conversion in the ${\rm H}_2 + {\rm H}_3^+$H2+H3+ → ${\rm H}_3^{+} +$H3++ H2 reaction

“…In this work we consider the full potential energy surface developed in Ref. 29, which describes correctly the asymptotic behavior for long distances and also the potential well, as it is shown in Fig. 1.…”

“…Rotational levels of H + 3 calculated with hyperspherical coordinates using the PES of Ref. 29. All the levels correspond to the ground (0, 0 0 ) vibrational state (with energy 4359.52 cm −1 for the non-physical state of j t = 0, taken as zero of energy), but different rotational states j t , ω t , and irreducible representation, , of the permutation-inversion group, isomorphic with the D 3h group.…”

“…The triatomic bound states were calculated with the PES of Ref. 29 in hyperspherical coordinates to properly assign the symmetry using an iterative Lanczos method, as described elsewhere. 40,41 The state-to-state cumulative reaction probabilities (CRPs), N sr,M s r (E), are given by…”

“…In the last years several PES's, of increasing accuracy, have appeared in the literature. [29][30][31][32][33][34][35] The exchange reaction barrier is rather low, below the zero-point energy, so that all identical nuclei can permute, subject to the symmetry constraints imposed by nuclear spin angular momenta, 23,24,26 as experimentally confirmed by measurements in plasmas at 300-500 K. 12,13 All this makes extremely difficult to perform complete quantum calculations including the 12 degrees of freedom (9 vibrational and 3 rotational), considering the whole permutation group of symmetry. For this aim, proper coordinates should be designed, as the democratic hyperspherical coordinates developed recently by Kuppermann.…”

“…Here, we shall use a global PES recently proposed which describes very satisfactorily the long-range interactions, going beyond the point charge model for H + 3 using a triatomics-in-molecules (TRIM) treatment. 29 The organization of the paper is as follows. In Sec.…”