The effects of pressure and temperature on the absorption coefficient of ammonia (NH3) gas self-perturbed and perturbed by nitrogen (N2) gas have been measured. We varied the gas pressure from 10 to 160 Torr and the temperature from 235 to 296？K in order to study the absorption coefficient at the center and the wings of lines in the band of NH3. These measurements were made using a high resolution (0.0038？cm？1) Bruker Fourier-transform spectrometer. These spectra have been analyzed using the method of multipressure technique permitting to succeed to an evolution of the absorption coefficient with the pressure and the quantum numbers and of the NH3 molecule. The results show that the absorption coefficient varies as a quadratic function of the pressure at the center of a given line. However, it has a linear evolution in the wings of the line. Moreover, the absorption coefficients are inversely proportional to temperature in the wings when NH3 lines are broadened by N2. The retrieved values of these coefficients were used to derive the temperature dependence of N2 broadening NH3 lines. The absorption coefficients were shown to fit closely the well-known exponential law. 1. Introduction The infrared spectroscopic investigations of the atmospheres of stars, planets, and their satellites, using infrared spectroscopy, not only provide valuable information about the chemical elements that they consist of, but also about the horizontal and the vertical distribution of their minor constituents. Due to the complexity of the line profiles used to model the spectral shapes (absorption, broadening, intensity), it is necessary to determine experimentally the line parameters of the spectra in order to test the models being used. Several studies in the literature have investigated the spectral properties of NH3 in several infrared bands. Aroui et al. [1] have studied the self-broadening and line intensities, Nouri et al. [2] have studied the temperature dependence of pressure broadening, and other authors [3, 4] were interested in the absorption coefficient at the line centers of NH3. Experimentally absorption coefficients for broadband ArF excimer radiation laser were determined for NH3 at temperatures up to 3500？K [5]. Measurements of the NH3 absorption coefficients at CO2 laser wavelengths have been done by Zelinger et al. [5] using photoacoustic spectroscopy. NH3 absorption coefficients were also measured by Allario and Seals [6] using several transitions of a CO2 laser for small concentrations of NH3 perturbed by N2. The influence of CO2 Laser line width on the
References
[1]
H. Aroui, S. Nouri, and J. P. Bouanich, “NH3 self-broadening coefficients in the and bands and line intensities in the band,” Journal of Molecular Spectroscopy, vol. 220, no. 2, pp. 248–258, 2003.
[2]
S. Nouri, J. Orphal, H. Aroui, and J. M. Hartmann, “Temperature dependence of pressure broadening of NH3 perturbed by H2 and N2,” Journal of Molecular Spectroscopy, vol. 227, no. 1, pp. 60–66, 2004.
[3]
D. F. Davidson, A. Y. Chang, K. Kohse-H？inghaus, and R. K. Hanson, “High temperature absorption coefficients of O2, NH3, and H2O for broadband ArF excimer laser radiation,” Journal of Quantitative Spectroscopy and Radiative Transfer, vol. 42, no. 4, pp. 267–278, 1989.
[4]
K. Benzerhouni, Absorption spectroscopy of ammonia and study of the laser (15NH3 + N2) for population inversion, Ph.D. thesis, Orsay, France, 1988.
[5]
Z. Zelinger, I. Jancik, and P. Engst, “Measurement of the NH3, CCl2F2, CHClF2, CFCl3, and CClF3 absorption coefficients at isotopic laser wavelengths by photoacoustic spectroscopy,” Applied Optics, vol. 31, no. 33, pp. 6974–6975, 1992.
[6]
F. Allario and R. K. Seals, “Measurements of NH3 absorption coefficients with a C13 laser,” Applied Optics, vol. 14, no. 9, pp. 2229–2233, 1975.
[7]
O. K. Voitsekhovskaya, E. N. Aksenova, and F. G. Shatrov, “Influence of CO2-laser linewidth on the measured absorption coefficients of atmospheric water vapor and ammonia,” Applied Optics, vol. 38, no. 12, pp. 2337–2341, 1999.
[8]
P. Jacquinot, “The luminosity of spectrometers with prisms, gratings, or Fabry Perot etalons,” The Journal of the Optical Society of America, vol. 44, pp. 761–765, 1954.
[9]
A. Predoi-Cross, G. C. Mellau, R. M. Lees, and B. P. Winnewisser, “Fourier transform infrared spectroscopy of the first CO-stretch overtone band of ,” Journal of Molecular Spectroscopy, vol. 189, no. 2, pp. 144–152, 1998.
[10]
S. Hadded, H. Aroui, J. Orphal, J. P. Bouanich, and J. M. Hartmann, “Line broadening and mixing in NH3 inversion doublets perturbed by NH3, He, Ar, and H2,” Journal of Molecular Spectroscopy, vol. 210, no. 2, pp. 275–283, 2001.
[11]
P. W. Rosenkranz, “Shape of the 5？mm oxygen band in the atmosphere,” IEEE Transactions on Antennas and Propagation, vol. 23, no. 4, pp. 498–506, 1975.
[12]
A. Lévy, N. Lacome, and C. Chackerian Jr., Spectroscopy of the Earth's Atmosphere and Interstellar Medium, Academic Press, New York, NY, USA, 1992.
[13]
H. Aroui, S. Nouri, and J. P. Bouanich, “NH3 self-broadening coefficients in the and bands and line intensities in the band,” Journal of Molecular Spectroscopy, vol. 220, no. 2, pp. 248–258, 2003.
[14]
R. Le Doucen, C. Cousin, C. Boulet, and A. Henry, “Temperature dependence of the absorption in the region beyond the 4.3- m band head of CO2. 1: pure CO2 case,” Applied Optics, vol. 24, no. 6, pp. 897–906, 1985.
[15]
C. Cousin, R. Le Doucen, C. Boulet, and A. Henry, “Temperature dependence of the absorption in the region beyond the 4.3- m band head of CO2 . 2: N2 and O2 broadening,” Applied Optics, vol. 24, no. 22, pp. 3899–3907, 1985.
[16]
H. Sasada, Y. Endo, E. Hirota, R. L. Poynter, and J. S. Margolis, “Microwave and Fourier-transform infrared spectroscopy of the and s states of NH3,” Journal of Molecular Spectroscopy, vol. 151, no. 1, pp. 33–53, 1992.
[17]
G. Shi and H. Zhang, “The relationship between absorption coefficient and temperature and their effect on the atmospheric cooling rate,” Journal of Quantitative Spectroscopy and Radiative Transfer, vol. 105, no. 3, pp. 459–466, 2007.
[18]
A. Bauer, M. Godon, J. Carlier, Q. Ma, and R. H. Tipping, “Absorption by H2O and H2O-N2 mixtures at 153 GHz,” Journal of Quantitative Spectroscopy and Radiative Transfer, vol. 50, no. 5, pp. 463–475, 1993.
