Accuracy of XH-stretching intensities with the Deng–Fan potential

ABSTRACT

One-dimensional local mode XH-stretching (X = ${}^{16}$O, ${}^{19}$F and ${}^{35}$Cl) vibrational transition frequencies and intensities have been calculated for six small atmospheric relevant molecules. The calculations are done using Morse, Deng–Fan and numeric potentials at the CCSD(T)/aug-cc-pVTZ level of theory. Parameters of the Morse potential are found from the derivatives of the potential energy surface, with respect to the internal XH-stretching displacement coordinate, evaluated at the equilibrium geometry. Parameters of the Deng–Fan potential are obtained using the first two transition frequencies of the Morse potential. The dipole moment functions (DMFs) are represented by a sixth-order polynomial in the displacement coordinate fitted to dipole moment single points calculated with a finite field approach. Analytical matrix elements are derived and used to calculate oscillator strengths for the Morse and Deng–Fan potential. We compare calculated and experimentally determined oscillator strengths and transition frequencies, as well as displacement matrix elements of the different potentials. For the XH-stretching vibrations considered, the Deng–Fan potential predicts absorption intensities considerably better than the Morse potential.

GRAPHICAL ABSTRACT

KEYWORDS:

• Vibrational transitions
• Deng–Fan analytical matrix elements
• Morse potential

Acknowledgements

This paper was inspired by the work of Martin L. Sage, and it grew out of a research project that he had embarked on at the time of his death. This paper is dedicated to his memory. We thank Aleksandrs Smilgins for helping us write a Matlab code to compute Deng–Fan oscillator strengths.

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Emil Vogt http://orcid.org/0000-0003-3335-9813

Daniel S. Sage http://orcid.org/0000-0002-0029-6062

Henrik G. Kjaergaard http://orcid.org/0000-0002-7275-8297

Additional information

Funding

We acknowledge the financial support from NSF (DMS-1503555) and the Center for Exploitation of Solar Energy founded by the University of Copenhagen.