Highly accurate HF dimer {\it ab initio} potential energy surface

A very accurate, (HF)$_2$ potential energy surface (PES)is constructed based on \ai\ calculations performed% at the CCSD(T) level of theory with an aug-cc-pVQZ-F12basis set at about 152~000 points.A higher correlation correction is computed at CCSDT(Q) level for 2000 points and is considered alongside other more minorcorrections due to relativity, core-valence correlation and Born-Oppenheimer failure.The analytical surface constructed uses 500 constants to reproduce the \ai\ points with a standard deviation of 0.3 \cm.Vibration-rotation-inversion energy levels of the HF dimer are computed for this PES by variational solution of the nuclear-motionSchr\"{o}dinger using program WAVR4. Calculations over an extended range of rotationally excited states show very good agreementwith the experimental data. In particular the known empirical rotational constants $B$ for the ground vibrational states are predicted to better than about 2 MHz.$B$ constants for excited vibrational states are reproduced several times more accurately than by previous calculations. %The experimental dissociation energy of the HF dimer is reproduced \ai\ within the experimental accuracy of about 1 \cm\ for the first time. This level of accuracy is shown to extend to higher excited inter-molecular vibrational states $v$ and higher excited rotational quantum numbers $(J,K_a)$

Symmetry adapted ro-vibrational basis functions for variational nuclear motion calculations: TROVE approach

We present a general, numerically motivated approach to the construction of symmetry adapted basis functions for solving ro-vibrational Schr\"{o}dinger equations. The approach is based on the property of the Hamiltonian operator to commute with the complete set of symmetry operators and hence to reflect the symmetry of the system. The symmetry adapted ro-vibrational basis set is constructed numerically by solving a set of reduced vibrational eigenvalue problems. In order to assign the irreducible representations associated with these eigenfunctions, their symmetry properties are probed on a grid of molecular geometries with the corresponding symmetry operations. The transformation matrices are re-constructed by solving over-determined systems of linear equations related to the transformation properties of the corresponding wavefunctions on the grid. Our method is implemented in the variational approach TROVE and has been successfully applied to a number of problems covering the most important molecular symmetry groups. Several examples are used to illustrate the procedure, which can be easily applied to different types of coordinates, basis sets, and molecular systems

The W2020 Database of Validated Rovibrational Experimental Transitions and Empirical Energy Levels of Water Isotopologues. II. H₂¹⁷O and H₂¹⁸O with an Update to H₂¹⁶O

The W2020 database of validated experimental transitions and accurate empirical energy levels of water isotopologues, introduced in the work of Furtenbacher et al. [J. Phys. Chem. Ref. Data 49, 033101 (2020)], is updated for H216O and newly populated with data for H217O and H218O. The H217O/H218O spectroscopic data utilized in this study are collected from 65/87 sources, with the sources arranged into 76/99 segments, and the data in these segments yield 27 045/66 166 (mostly measured) rovibrational transitions and 5278/6865 empirical energy levels with appropriate uncertainties. Treatment and validation of the collated transitions of H216O, H217O, and H218O utilized the latest, XML-based version of the MARVEL (Measured Active Rotational-Vibrational Energy Levels) protocol and code, called xMARVEL. The empirical rovibrational energy levels of H217O and H218O form a complete set through 3204 cm-1 and 4031 cm-1, respectively. Vibrational band origins are reported for 37 and 52 states of H217O and H218O, respectively. The spectroscopic data of this study extend and improve the data collated by an International Union of Pure and Applied Chemistry Task Group in 2010 [J. Tennyson et al., J. Quant. Spectrosc. Radiat. Transfer 110, 2160 (2010)] as well as those reported in the HITRAN2016 information system. Following a minor but significant update to the W2020-H216O dataset, the joint analysis of the rovibrational levels for the series H216O, H217O, and H218O facilitated development of a consistent set of labels among these three water isotopologues and the provision of accurate predictions of yet to be observed energy levels for the minor isotopologues using the combination of xMARVEL results and accurate variational nuclear-motion calculations. To this end, 9925/8409 pseudo-experimental levels have been derived for H217O/H218O, significantly improving the coverage of accurate lines for these two minor water isotopologues up to the visible region. The W2020 database now contains almost all of the transitions, apart from those of HD16O, required for a successful spectroscopic modeling of atmospheric water vapor

Analysis of the Red and Green Optical Absorption Spectrum of Gas Phase Ammonia

Room temperature NH3 absorption spectra recorded at the Kitt Peak National Solar Observatory in 1980 are analyzed. The spectra cover two regions in the visible: 15,200 - 15,700 cm-1 and 17,950 - 18,250 cm-1. These high overtone rotation-vibration spectra are analyzed using both combination differences and variational line lists. Two variational line lists were computed using the TROVE nuclear motion program: one is based on an ab initio potential energy surface (PES) while the other used a semi-empirical PES. Ab initio dipole moment surfaces are used in both cases. 95 energy levels with J = 1 - 7 are determined from analysis of the experimental spectrum in the 5vNH (red) region and 46 for 6vNH (green) region. These levels span four vibrational bands in each of the two regions, associated with stretching overtones

Vibrational energies of PH3 calculated variationally at the complete basis set limit

The potential energy surface for the electronic ground state of PH3 was calculated at the CCSD(T) level using aug-cc-pV(Q+d)Z and aug-cc-pVQZ basis sets for P and H, respectively, with scalar relativistic corrections included. A parametrized function was fitted through these ab initio points, and one parameter of this function was empirically adjusted. This analytical PES was employed in variational calculations of vibrational energies with the newly developed program TROVE. The convergence of the calculated vibrational energies with increasing vibrational basis set size was improved by means of an extrapolation scheme analogous to the complete basis set limit schemes used in ab initio electronic structure calculations. The resulting theoretical energy values are in excellent agreement with the available experimentally derived values

THE RENNER EFFECT IN THE X~{\widetilde X}\,\,2A′′^2\hspace*{-1mm}A'' AND A~{\widetilde A}\,\,2A′^2\hspace*{-1mm}A' ELECTONIC STATES OF HSO/HOS

Author Institution: Institute of Applied Physics, Russian Academy of Science; Ulyanov Street 46, Nizhny Novgorod, Russia 603950, and; Physical and Theoretical Chemistry, Faculty of Mathematics and Natural Sciences, University of Wuppertal, D-42097 Wuppertal, Germany; Physical and Theoretical Chemistry, Faculty of Mathematics and Natural Sciences, University of Wuppertal, D-42097 Wuppertal, Germany; Department of Chemistry, Faculty of Science, Ochanomizu University, 2-1-1 Otsuka, Bunkyo-ku, Tokyo 112-8610, JapanWe report a theoretical investigation of the ${\widetilde X}$\,\,$^2\hspace*{-1mm}A''$ and ${\widetilde A}$\,\,$^2\hspace*{-1mm}A'$ electronic states of HSO/HOS. Both electronic states have nonlinear equilibrium geometries and they correlate with a $^{2}\Pi$ state at linearity so that they exhibit the Renner effect. In highly excited bending states, there is tunneling between two minima (with the H nucleus bound to the O or S nucleus, respectively) separated by a potential energy barrier of 17224.3~cm$^{-1}$. The linear geometry H-O-S is accessible to the molecule; the corresponding barrier is 11877.3~cm$^{-1}$. However, the barrier to the H-S-O linear geometry is 34775.2~cm$^{-1}$ and we take this geometry to be inaccesible to the molecule since at such a large potential energy, our potential energy surfaces are not well defined and an an accurate calculation of the rovibronic energies is not possible at the present time. So in practice we consider only a single Renner effect here, namely that at the H-O-S linear geometry. Three-dimensional potential energy surfaces for the ${\widetilde X}$\,\,$^2\hspace*{-1mm}A''$ and ${\widetilde A}$\,\,$^2\hspace*{-1mm}A'$ electronic states of HSO have been calculated \textit{ab initio} by the MR-SDCI+Q/[aug-cc-pCVQZ (S, O), aug-cc-pVQZ (H)] method, and the global potential energy surfaces for the states have been constructed. These surfaces have been used, in conjunction with the computer program DR [Odaka \textit{et al.}, J. Mol. Structure \textbf{795}, 14 (2006); Odaka \textit{et al.}, J. Chem. Phys. \textbf{126}, 094301 (2007)], for calculating HSO/HOS rovibronic energies in the electronic states ${\widetilde X}$\,\,$^2\hspace*{-1mm}A''$ and ${\widetilde A}$\,\,$^2\hspace*{-1mm}A'$. The results and analysis of the \textit{ab initio} calculations, the rovibronic energies obtained, and analyses of the wavefunction for selected states will be presented

The Renner Effect in the X̃ ²A″ and à ²A′ Electronic States of HSO/HOS

We report a theoretical investigation of the X̃ ²A″ and à ²A′ electronic states of HSO/HOS. Three-dimensional potential energy surfaces for the X̃ ²A″ and à ²A′ electronic states of HSO/HOS have been calculated ab initio by the core-valence MR-SDCI+<i>Q</i>/[aug-cc-pCVQZ­(S,O),aug-cc-pVQZ­(H)] method, and near-global potential energy surfaces have been constructed. These surfaces have been used, in conjunction with our computer program DR, for calculating HSO/HOS rovibronic energies in the electronic states X̃ ²A″ and à ²A′. Both electronic states have nonlinear equilibrium geometries and they correlate with ²Π states at the H–S–O and H–O–S linear configurations so that they exhibit the double Renner effect. The present DR calculation of the rovibronic energies for the X̃ ²A″ and à ²A′ electronic states of HSO/HOS is complicated by the Renner-interaction breakdown of the Born–Oppenheimer approximation and by HSO/HOS isomerization. Calculated energies are reported together with analyses of the rovibronic wave functions for selected states. These analyses explore the interplay between the effects of, on one hand, Renner interaction and, on the other hand, isomerization tunneling in the rovibronic dynamics of HSO/HOS