Abstract
Two sets of NH3 absorption spectra covering the 0.793 μm region are recorded using two Bruker IFS 125 HR Fourier transform spectrometers. Three unapodized absorption spectra are recorded in Brussels over the range 11000−14500 cm−1 and the positions and intensities of 1114 ammonia lines observed in the 12491−12810 cm−1 region are measured using a multi-spectrum least squares fitting algorithm. 367 additional lines are identified in an ammonia absorption spectrum recorded in two steps at the J. Heyrovsky Institute of Physical Chemistry in Prague, using two different interference filters covering the 12000−12500 and 12400−13000 cm−1 ranges. The 1481 measured ammonia lines are analyzed using an empirical line list computed using variational nuclear motion calculations and ground state combination differences. Transitions are assigned to vibrational states with 4νNH stretching excitation (v1+v3=4). 278 out of the 1481 measured lines are assigned to 300 transitions and 119 upper state energy levels are derived from the frequencies of the assigned transitions.
Highlights
Complete characterization of ammonia molecular spectra in the microwave, infrared and optical ranges represents one of the major aims of both fundamental as well as applied high resolution molecular spectroscopy
Ammonia rovibrational levels derived from the line positions assigned in the 4νNH region: Observed and calculated energies and corresponding differences, and errors in the combination differences (CD)
The absorption spectrum of ammonia near 0.793 μm has been recorded at high resolution using two Fourier transform spectrometers, in Brussels and Prague
Summary
Complete characterization of ammonia molecular spectra in the microwave, infrared and optical ranges represents one of the major aims of both fundamental as well as applied high resolution molecular spectroscopy. Fortney et al [11] recently suggested that hotter gas giants should show pronounced ammonia features, emphasizing the importance of characterizing highly excited vibrational states of ammonia All these applications require accurate spectroscopic data over extended frequency and temperatures ranges. The need to improve the representation of the data in ammonia is illustrated by a recent study of the visible spectrum of ammonia on Jupiter [9] which showed that the CoYuTe variational line list [34] gave a good representation of the shape of the observed features but showed a shift in wavelength which can be attributed to the lack of experimental energy levels to which the line list could be tuned This behavior is found in our analysis below.
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