*Ab initio*calculations of the electronic states of AsH

_{2}including dissociation characteristics

^{1,a)}, Robert J. Buenker

^{1}and Heinz–Peter Liebermann

^{1}

### Abstract

Multireference configuration interaction calculations have been carried out for low-lying electronic states of AsH_{2}. Bending potentials for the ten lowest states of AsH_{2} are obtained in *C* _{2v } symmetry for As–H distances fixed at the the ground state equilibrium value of 2.845 *a* _{0}, as well as for the minimum energy path constrained to *R* _{1} = *R* _{2}. The calculated equilibrium geometries for the ground state and the excited state agree very well with the previous experimental and theoretical results, whereas the data for the higher-lying states are obtained for the first time. Asymmetric potential energy surface (PES) cuts (at *R* _{1} = 2.845 *a* _{0}, θ = 90.7°) and two-dimensional (2D) PESs for the lowest three states are also new. The calculated *ab initio* data are used for analysis of possible AsH_{2}photodissociation channels and predissociation effects. It is shown that the transition dipole moment decreases with increasing bending angle, which influences the intensity distribution in the emission spectrum ( bending series), shifting its maximum to smaller quantum numbers.

I. INTRODUCTION

II. COMPUTATIONAL METHOD

III. RESULTS AND DISCUSSION

A. Bending potential energy curves

B. Asymmetric stretch potential energy curves

C. The transition moment

IV. CONCLUSION

V. ACKNOWLEDGMENTS

### Key Topics

- Ground states
- 19.0
- Dissociation
- 17.0
- Excitation energies
- 16.0
- Dissociation energies
- 12.0
- Emission spectra
- 12.0

## Figures

Bending PESs for the low-lying states of AsH_{2} computed at *R* = 2.845 *a* _{0} = without including SO coupling. The ^{2} *A* _{1} and ^{2} *B* _{1} states are shown in black, ^{2} *B* _{2} – in blue, ^{4} *B* _{1} and ^{4} *A* _{2} – in green. The vertical dashed line indicates an equilibrium angle (θ = 90.7°) for the ground state.

Bending PESs for the low-lying states of AsH_{2} computed at *R* = 2.845 *a* _{0} = without including SO coupling. The ^{2} *A* _{1} and ^{2} *B* _{1} states are shown in black, ^{2} *B* _{2} – in blue, ^{4} *B* _{1} and ^{4} *A* _{2} – in green. The vertical dashed line indicates an equilibrium angle (θ = 90.7°) for the ground state.

Minimal energy path PESs for the low-lying states of AsH_{2} computed in *C* _{2} _{ v } symmetry without including SO coupling. The ^{2} *A* _{1} and ^{2} *B* _{1} states are shown in black, ^{2} *B* _{2} and ^{2} *A* _{2} – in blue, ^{4} *B* _{1} and ^{4} *A* _{2} – in green. The *D* _{∞h } notation is used for the linear geometry.

Minimal energy path PESs for the low-lying states of AsH_{2} computed in *C* _{2} _{ v } symmetry without including SO coupling. The ^{2} *A* _{1} and ^{2} *B* _{1} states are shown in black, ^{2} *B* _{2} and ^{2} *A* _{2} – in blue, ^{4} *B* _{1} and ^{4} *A* _{2} – in green. The *D* _{∞h } notation is used for the linear geometry.

PESs for the low-lying states of AsH_{2} as functions of the As–H_{2} distance computed for *R*(H-H) = 1.40 *a* _{0} ≃ *R* _{ e }(H_{2}) without SO coupling.

PESs for the low-lying states of AsH_{2} as functions of the As–H_{2} distance computed for *R*(H-H) = 1.40 *a* _{0} ≃ *R* _{ e }(H_{2}) without SO coupling.

Computed asymmetric stretch PESs for the low-lying states of AsH_{2} obtained for *R* _{1} = 2.845 *a* _{0} and θ = 90.7° without including SO coupling.

Computed asymmetric stretch PESs for the low-lying states of AsH_{2} obtained for *R* _{1} = 2.845 *a* _{0} and θ = 90.7° without including SO coupling.

Calculated PESs for the , , and ^{4} *A* ^{″} −states of AsH_{2} along one As–H bond distance and the H–As–H angle θ. The other As–H distance is fixed at the ground state equilibrium value of 2.845 *a* _{0}.

Calculated PESs for the , , and ^{4} *A* ^{″} −states of AsH_{2} along one As–H bond distance and the H–As–H angle θ. The other As–H distance is fixed at the ground state equilibrium value of 2.845 *a* _{0}.

Calculated electric dipole moment for the transition obtained for the minimal energy path geometry of the state. The crosses show the calculated points, the curve corresponds to the polynomial fit.

Calculated electric dipole moment for the transition obtained for the minimal energy path geometry of the state. The crosses show the calculated points, the curve corresponds to the polynomial fit.

## Tables

Vertical excitation energies, leading configurations, and dipole transitions moments calculated without SO coupling for the lowest electronic states of AsH_{2} at the ground state equilibrium geometry.

Vertical excitation energies, leading configurations, and dipole transitions moments calculated without SO coupling for the lowest electronic states of AsH_{2} at the ground state equilibrium geometry.

MRD–CI geometries and energies for selected features in the bending potentials of AsH_{2}. Notation *min* and *max* used in the second column corresponds to the local extrema in the Λ − *S* bending PESs.

MRD–CI geometries and energies for selected features in the bending potentials of AsH_{2}. Notation *min* and *max* used in the second column corresponds to the local extrema in the Λ − *S* bending PESs.

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