Analysis of the red and green optical absorption spectrum of gas phase ammonia

Nikolai F Zobov,Phillip A Coles,Roman I Ovsyannikov,Aleksandra A Kyuberis,Robert J Hargreaves,Peter F Bernath,Jonathan Tennyson,Sergei N Yurchenko,Oleg L Polyansky

doi:10.1016/j.jqsrt.2018.02.001

Abstract

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 5νNH (red) region and 46 for 6νNH (green) region. These levels span four vibrational bands in each of the two regions, associated with stretching overtones.

Highlights

There are a number of reasons why one might attempt to analyse the high resolution optical ro-vibrational spectrum of ammonia
For almost 70 years, the vibration-rotation spectrum of 14NH3 was only studied in detail at wavelengths longer than 2 μm; these spectra are assembled in comprehensive high resolution molecular spectroscopic databases such as the 2008 edition of HITRAN [1]
This is especially true for states of high vibrational excitation such as those found in its visible spectrum

Summary

Introduction

There are a number of reasons why one might attempt to analyse the high resolution optical ro-vibrational spectrum of ammonia. For almost 70 years, the vibration-rotation spectrum of 14NH3 was only studied in detail at wavelengths longer than 2 μm; these spectra are assembled in comprehensive high resolution molecular spectroscopic databases such as the 2008 edition of HITRAN [1]. This is especially true for states of high vibrational excitation such as those found in its visible spectrum. Transitions at visible wavelengths provide a pathway to the study of the spectrum of ammonia up to and beyond dissociation. Visible wavelength spectra have been available for some time Ammonia lines in this region were observed at Kitt Peak in 1980, but remained unanalyzed; see section. Rotational assignments were given for 318 and 105 lines respectively in the two regions These partial (rotational) assignments do not supply information on the upper vibrational state. 0.0001 0.0004 −0.0046 −0.0043 −0.0021 0.0026 −0.0019 0.0025 −0.0045 0.0006 −0.0047 0.0052 −0.0041 −0.0030 −0.0007 −0.0047 calc.ref

Experimental observation of ammonia spectra

Spectral analysis

Comparison with previous work

Conclusion