The barrier to linearity of water

Abstract

High-quality ab initio quantum chemical methods, including higher-order coupled cluster (CC) and many-body perturbation (MP) theory, explicitly correlated (linear R12) techniques, and full configuration interaction (FCI) benchmarks, with basis sets ranging from [O/H] [3s2p1d/2s1p] to [8s7p6d5f4g3h2i/7s6p5d4f3g2h] have been employed to obtain the best possible value for the barrier to linearity of water. Attention is given to the degree of accord among extrapolations of conventional MP2, CCSD, and CCSD(T) energies to the complete basis set (CBS) limit and corresponding linear R12 schemes for these correlation methods. Small corrections due to one- and two-particle relativistic terms, core correlation effects, and the diagonal Born–Oppenheimer correction (DBOC) have been incorporated. The final electronic (vibrationless) extrapolated barrier height of this study is 11 127±35 cm−1. Anharmonic force fields have been determined at the aug-cc-pCVTZ CCSD(T) level at equilibrium and at a linear reference geometry. These and previous sextic force fields are in general accord with the expansion terms of recent global potential energy hypersurfaces but also highlight some of their weaknesses.

Dipole Correlation of the Electronic Structures of theConformations of Water Molecule Evolving Through theNormal Modes of Vibrations Between Angular (C2v) to Linear(D∝h) Shapes

“…Foster and Weinhold [56], by an NBO analysis, obtained a similar result on the pattern of hybridization in the linear structure of H 2 O molecule. Thus the computed structural effect following the dynamic evolution of conformation of water molecule is consistent with experimental [3,4,5,6] and theoretical [42] observations relating to such process. …”

“…It is transparent from the results that the magnitude of 'O-H' bond energy is a monotone increasing function of the evolution of conformations of water molecule with the gradual opening of ∠HOH angle. This may be equivalently stated that the stretching frequency of 'O-H' bond is a monotone increasing function of the evolution of conformations of water molecule with the gradual opening of ∠HOH bond angle It may be cited that a similar shortening of bond length and increasing of stretching frequency 'O-H' bond during the physical process of gradual opening of the ∠HOH angle was observed in a much more refined calculation of Schaefer III et al [42]. Evaluated quantum mechanical environment dependent hybridization as a function of structural evolution demonstrates that, at each stage of evolution of conformation, the molecule rehybridizes.…”

“…The water molecule occurs in angular shape (C 2v ) in the equilibrium geometry and evolves, following the normal modes of vibrations, to linear form (D ∝h ), the transition state for inversion. It may be pointed out that the magnitude of barrier to the linearity of water is quite high [41,42]. It has been opined by many workers that the stretching frequency of the 'O-H' bond of water molecule both in ground and excited vibrational levels is worthy of investigation [3,4,5,6].…”

Global spectroscopy of the water monomer

“…In final form, PT-based effective Hamiltonians for asymmetric tops were formulated by Watson [18]. Owing to the lightness and in particular the quasi-linearity of the water molecule [19,20], PT series for water converge very slowly, or indeed sometimes not at all. Unlike other molecules, whose spectra are often fitted to effective Hamiltonians with experimental accuracy, MMW, sub-MMW and IR data on water have never been fitted to a polynomial Hamiltonian to the accuracy of the underlying experiment; a recent demonstration was provided by Furtenbacher & Császár [21].…”

Second-order Møller–Plesset calculations on the water molecule using Gaussian-type orbital and Gaussian-type geminal theory

“…The accurate calculation of the basis-set limit of the correlation correction to this barrier is therefore a stringent test for explicitly correlated methods 33,34 and, in particular, for the MP2-GGn method.…”