10min:

N. IBRAHIM, P. CHELIN AND J. ORPHAL, Laboratoire Interuniversitaire des Systèmes Atmosphériques (LISA), CNRS and Universités Paris-7 et -12, Créteil, France; C. E. FELLOWS, Laboratório de Espectroscopia e Laser, Instituto de Física, Universidade Federal Fluminense, Niterói, Rio de Janeiro, Brazil.

The near-infrared absorption spectrum of NH₃ is an interesting opportunity for atmospheric in-situ measurements of this species using tuneable diode-lasers. For this purpose, accurate line positions and intensities are indispensable.

In the past, several studies of the absorption spectrum of ¹⁴NH₃ in the near-infrared were carried out, using Fourier-transform¹ and tuneable diode-laser spectroscopy.^2-4 More recently, high-resolution diode-laser spectra of ¹⁵NH₃ were analyzed for the first time.⁵ The lines of ¹⁴NH₃ in this region are also useful for wavenumber calibration of absorption spectra obtained with tuneable lasers.

In our group, we have recently investigated the possibility to detect atmospheric NH₃ using photoacoustic laser spectroscopy in the 1.5 µm region, and observed several discrepancies between individual line positions and intensities observed in our and previous studies^1,4, as already noticed by other groups.^2,5 In order to solve this problem we have measured new absorption spectra of ¹⁴NH₃ (and also of ¹⁵NH₃) in the 6300-7500 cm^-1 region using a Bruker IFS 120-HR Fourier-transform spectrometer. The length of the absorption cell was 30 cm. The NH₃ pressures employed were around 30 mbar, and the spectral resolution used was 0.02 cm^-1, leading to linewidths (Full-Width at Half-Maximum) of about 0.03 cm^-1. Based on these spectra, we have produced a list of individual line positions and line intensities at 296 K. Comparisons with the previous studies^1-5 will be presented.