*ab initio*potential surface and dipole moment surface

^{1}and Joel M. Bowman

^{1,a)}

### Abstract

We report a full dimensional, *ab initio*-based global potential energy surface (PES) and dipole momentsurface for . Both surfaces are symmetric with respect to interchange of the H atoms. The PES is a fit to thousands of electronic energies calculated using the coupled-cluster method [CCSD(T)] with a moderately large basis (aug-cc-pVTZ). Vibrational energies and wave functions are accurately obtained using MULTIMODE. The wave function and dipole momentsurface are used to calculate and analyze the pure infrared spectrum at which is compared with experiment. Vibrational energies and the infrared spectra for DOD and HOD/DOH are also presented.

We thank Joseph Roscioli and Mark Johnson for sending the experimental spectrum, Xinchuan Huang for help with MULTIMODE calculations and for fitting the dipole moment surface, and Stuart Carter for addressing coding issues with respect to MULTIMODE. We thank the ONR (N00014-05-1-0460) for financial support.

I. INTRODUCTION

II. CALCULATIONS

A. Potential energy surface

B. Dipole surface

C. Vibrational calculations

D. IR spectrum

III. RESULTS AND DISCUSSION

A. Potential energy surface

B. Dipole momentsurface

C. Vibrational calculations, IR spectra, and comparison with experiment

D. IR spectra of isotopologs

IV. SUMMARY AND CONCLUSIONS

### Key Topics

- Infrared spectra
- 20.0
- Electric dipole moments
- 19.0
- Ab initio calculations
- 14.0
- Wave functions
- 13.0
- Normal modes
- 11.0

## Figures

Sketch of one-dimensional potential energy cut along the isomerization path with corresponding geometries. I, II, and III define the grid regions as described in the text. *Ab initio* barrier height of the transition state is .

Sketch of one-dimensional potential energy cut along the isomerization path with corresponding geometries. I, II, and III define the grid regions as described in the text. *Ab initio* barrier height of the transition state is .

Potential energy cuts along each normal mode (mass scaled). Mode numbering corresponds to increasing harmonic frequency (given in Table I). Insets are pictures of the corresponding modes.

Potential energy cuts along each normal mode (mass scaled). Mode numbering corresponds to increasing harmonic frequency (given in Table I). Insets are pictures of the corresponding modes.

Root mean square (rms) fitting error as a function of data cutoff energy.

Root mean square (rms) fitting error as a function of data cutoff energy.

Contour plot of the potential energy surface for with fixed at the asymmetric equilibrium configuration of the global minimum in the variables and the planar rotation angle . equals 0 when the vector bisects the HOH bond angle and is positive as moves in the direction of the ionic H and negative when moves toward the free H.

Contour plot of the potential energy surface for with fixed at the asymmetric equilibrium configuration of the global minimum in the variables and the planar rotation angle . equals 0 when the vector bisects the HOH bond angle and is positive as moves in the direction of the ionic H and negative when moves toward the free H.

Cuts of dipole moment components for normal modes against mass-weighted normal mode coordinates . Note that only mode 3 has a nonzero component.

Cuts of dipole moment components for normal modes against mass-weighted normal mode coordinates . Note that only mode 3 has a nonzero component.

Convergence of six fundamental energies, obtained by CI calculations, as a function of the -mode representation of the potential mode coupling for where represents the number of modes being coupled.

Convergence of six fundamental energies, obtained by CI calculations, as a function of the -mode representation of the potential mode coupling for where represents the number of modes being coupled.

Experimental (Ref. 4) and calculated IR spectra of in the low-frequency portion of the experimental spectrum. Intensity is given in arbitrary units and is normalized to the intensity of the band.

Experimental (Ref. 4) and calculated IR spectra of in the low-frequency portion of the experimental spectrum. Intensity is given in arbitrary units and is normalized to the intensity of the band.

Wave function contour plots of the and states as functions of the normal and and and .

Wave function contour plots of the and states as functions of the normal and and and .

Cuts of , , and components of the dipole with respect to the out-of-plane normal coordinate for the indicated fixed values of , the ionic OH stretch normal mode.

Cuts of , , and components of the dipole with respect to the out-of-plane normal coordinate for the indicated fixed values of , the ionic OH stretch normal mode.

High-frequency range of the IR spectrum for both experiment (Refs. 4 and 36) and theory. Intensity is given in arbitrary units and is normalized to the intensity of the band. The low-intensity bands have been blown up as an inset in the theoretical spectrum.

High-frequency range of the IR spectrum for both experiment (Refs. 4 and 36) and theory. Intensity is given in arbitrary units and is normalized to the intensity of the band. The low-intensity bands have been blown up as an inset in the theoretical spectrum.

IR spectra of isotopologs indicated, where notation indicates the is immediately followed by the ionic H/D. Intensities are normalized to the absolute intensity of the band.

IR spectra of isotopologs indicated, where notation indicates the is immediately followed by the ionic H/D. Intensities are normalized to the absolute intensity of the band.

## Tables

Comparison of vibrational frequencies (in ) for fundamentals and various overtones and combination bands of from the present calculations, denoted PES-CI, previous calculations, as indicated and described in detail in the text, and experiment. Also shown are the harmonic frequencies (HO) directly from *ab initio* calculations and the fitted potential energy surface.

Comparison of vibrational frequencies (in ) for fundamentals and various overtones and combination bands of from the present calculations, denoted PES-CI, previous calculations, as indicated and described in detail in the text, and experiment. Also shown are the harmonic frequencies (HO) directly from *ab initio* calculations and the fitted potential energy surface.

Band frequencies (in ) and intensities (arbitrary units) and normalized intensities from the present CI calculations. Assignment is based on the CI eigenvectors obtained from the diagonalization of the Hamiltonian matrix in the basis of virtual states.

Band frequencies (in ) and intensities (arbitrary units) and normalized intensities from the present CI calculations. Assignment is based on the CI eigenvectors obtained from the diagonalization of the Hamiltonian matrix in the basis of virtual states.

Vibrational frequencies in and intensities in arbitrary units of IR spectral bands for and isotopologs indicated.

Vibrational frequencies in and intensities in arbitrary units of IR spectral bands for and isotopologs indicated.

Article metrics loading...

Full text loading...

Commenting has been disabled for this content