Rovibrational energy levels of the F⁻(H₂O) and F⁻(D₂O) complexes

Abstract

The variational nuclear-motion codes ElVibRot and GENIUSH have been used to compute rotational-vibrational states of the F(-)(H2O) anion and its deuterated isotopologue, F(-)(D2O), employing a full-dimensional, semiglobal potential energy surface (PES) called SLBCL, developed as part of this study for the ground electronic state of the complex. The PES is determined from all-electron, explicitly correlated coupled-cluster singles, doubles, and connected triples [CCSD(T)-F12a] computations with an atom-centered, fixed-exponent Gaussian basis set of cc-pCVTZ-F12 quality. The SLBCL PES accurately reproduces the two equivalent minima of the complex, the corresponding transition barrier of C2v point-group symmetry, as well as the proton transfer and the dissociation asymptotes towards the products HF + OH(-) and F(-) + H2O, respectively. The code ElVibRot has been updated so that it can use curvilinear internal coordinates corresponding to a reaction path. The variationally computed vibrational energy levels are compared to relevant experimental and previously determined first-principles results. The vibrational states reveal the presence of pronounced anharmonic effects and considerable intermode couplings resulting in strong resonances, involving in particular the HOH bend and the ionic OH stretch motions. Tunneling results in particularly significant splittings for F(-)(H2O); as expected, the splittings are orders of magnitude smaller for the F(-)(D2O) molecule. The rovibrational energy levels reveal that, despite the large-amplitude vibrational motions, the rotations of F(-)(H2O) basically follow rigid-rotor characteristics.

Feshbach resonances in the F + H2O → HF + OH reaction

“…The photodetachment of the FH 2 O − anion is also investigated quantum mechanically in fulldimensions on the new accurate NN PES. The anion PES is a newly constructed one by this group based on 11,936 CCSD(T)-F12a/(O and F: cc-pCVTZ-F12, H: cc-pVTZ-F12) 36 ab initio energies with fundamental invariants NN (FI-NN) method 37 , yielding a root-mean-square-error of 0.043 meV. The ground rovibrational eigenstate on the anion PES is calculated and vertically projected onto the neutral PES for a continuous propagation using the diatom-diatom Jacobi coordinates.…”

Vibrational spectra of halide-water dimers: Insights on ion hydration from full-dimensional quantum calculations on many-body potential energy surfaces

“…In addition, since the potential energy surface (PES) of the halide-water dimers display two equivalent global minima with C s symmetry separated by a C 2v saddle point along the in-plane water rocking motion, the intermolecular vibrational levels may split due to quantum tunneling. [5][6][7] This makes the theoretical assignment of the different absorption peaks observed in the experimental spectra particularly challenging, requiring both an accurate PES and a rigorous treatment of the nuclear motion at the quantum-mechanical level.…”

“…10 More recently, anharmonic vibrational frequencies have been calculated for both F − (H 2 O) and F − (D 2 O) dimers using a variational method called GENIUSH and a semiglobal PES derived from CCSD(T)-F12a data. 6 The GENIUSH method employs the internal coordinates and direct product DVR (discrete variable representation) basis. The acronym GENIUSH stands for general (GE) rovibrational code with numerical (N), internalcoodinate (I), user-specified (US) Hamiltonians (H).…”

Effects of vibrational excitation on the F + H2O → HF + OH reaction: dissociative photodetachment of overtone-excited [F–H–OH]−

“…The structure and energetics of the F – (H 2 O) anion itself have garnered significant attention from both experimental and theoretical perspectives. 36 – 49 Johnson and coworkers used vibrational predissociation of F – (H 2 O)·Ar complexes to measure infrared spectra over 600–3800 cm –1 , producing spectra dominated by the ionic hydrogen bond (IHB) that shuttles the shared proton between the F and O atoms. 38 , 41 , 42 , 44 Features attributed to the fundamental and overtone of this mode were found to be strongly blue-shifted upon complexation with Ar, while Cl – (H 2 O)·Ar and Br – (H 2 O)·Ar are slightly red-shifted for the comparable mode.…”

“…Although calculated vibrational frequencies using this reduced-dimensionality approach were found to yield reasonable results, it was determined that a 2D model based on coupling between the OF stretch and the motion of the shared proton gave the most accurate results compared to the available experimental data for the F – (H 2 O) system. 44 A number of recent theoretical studies have examined the vibrational structure of F – (H 2 O) at a much higher level of theory, 45 , 47 , 49 including recent full dimensionality simulations of the photodetachment spectra of vibrationally excited F – (H 2 O), showing that excitation of the IHB accesses the more charge delocalized FH···OH – structure of the anion resulting in a change in the photoelectron spectrum. 48 The effects of excitation of this anion IHB mode on the dissociative photodetachment of F – (H 2 O) is the focus of the present study.…”