2
𝝂
𝟒
+ 𝝂
𝟓
Tuong Le Cong
1
, Laurent Fissiaux
1,a
, Ha Tran
2
,
Muriel Lepère 1
1
Laboratory Lasers and Spectroscopies (LLS), Research centre in Physics of Matter and
Radiation (PMR), University of Namur,
61, rue de Bruxelles, B-5000 Namur, Belgium.
2
Laboratoire Interuniversitaire des Systèmes Atmosphériques (LISA), Université Paris Est Créteil,
Université Paris Diderot, Institut Pierre-Simon Laplace F-94010 Créteil Cedex, France.
Acetylene is a minor component of our atmosphere [1] as well as of the atmospheres of Mars [2],
Jupiter [3], Titan [4], Uranus [5-6], and Neptune [7]. It has been suggested that by 2030 the concentration of C
2
H
2
in the Earth’s atmosphere would reach 150% of its value in the 1990s due to increased use of automobiles worldwide [8]. Consequently, it has been the subject of several high resolution spectroscopic studies, especially on collisional broadening. To our knowledge, no
O
2
-broadening coefficients of
12
C
2
H
2
in the 𝜈
4
+ 𝜈
5
band have been yet reported.
In this work, we have measured O
2
-broadening coefficients for 21 absorption lines in the 𝜈
4 band of
12
C
2
H
2
+ 𝜈
5
at room temperature using a diode-laser spectrometer [9]. These lines with J values up to 23 were located in spectral range from 1275 to 1380 cm
-1
. For each studied line, the broadening spectra were recorded at four different pressures of oxygen ranging from 20.00 to 66.21 mbar.
The O
2
-collisional broadening coefficients of C
2
H
2
were retrieved by fitting the experimental profiles to the Voigt line-shape [10] as well as the Rautian [11], and Galatry [12] models which take into account the collisional narrowing due to molecular confinement (Dicke effect) [13]. Finally, our results are compared with a previous study realized in 𝜈
5
band of acetylene [14]. a Post-doctoral researcher with F.R.S.-FNRS (Belgium)
References
[1] R.A. Whitby, E.R. Altwicker, Atmos. Environ. 12 , 1289-1296 (1978)
[2] D. Horn, J.M. McAfee, A.M. Winer, K.C. Herr, G.C. Pimentel, Icarus 16 , 543-556 (1972)
[3] P.V. Sada, G.L. Bjoraker, D.E. Jennings, G.H. McCabe, P.N. Romani, Icarus 136 , 192-201 (1998)
[4] R.J. Vervark Jr, B.R. Sandel, D.R. Strobel, Icarus 170 , 91-112 (2004)
[5] M. Burgdorf, G. Orton, J. van Cleve, V. Meadows, J. Houck, Icarus 184 , 634-637 (2006)
[6] J. Bishop, K. Atreya, F. Herbert, P. Romani, Icarus 88 , 448-464 (1990)
[7] B. Conrath, F.M. Flasar, R. Hanel, V. Kunde, W. Maguire, J. Pearl, et al. Science 246 , 1454-1459
(1986)
[8] P. Varanasi, L.P. Giver, F.P.J. Valero, J. Quant. Spectrosc. Radiat. Transfer 30 , 505-509 (1983)
[9] L. Fissiaux, G. Blanquet, M. Lepère, J. Quant. Spectrosc. Radiat. Transfer 113 , 1233-1239
(2012)
[10] B.H. Armstrong, J. Quant. Spectrosc. Radiat. Transfer. 7 , 61-88 (1967)
[11] S.G. Rautian, I.I. Sobel’man, Sov. Phys. Usp. Engl. Transl. 9 , 701-716 (1967)
[12] L. Galatry, Phys. Rev. 122 , 1218-1224 (1960)
[13] R.H. Dicke, Phys. Rev. 89 , 472-473 (1953)
[14] D. Lambot, G. Blanquet, J.P. Bouanich, J. Mol. Spectrosc. 136 , 86-92 (1989)

Introduction
Acetylene is a minor component of our atmosphere [1] as well as of the atmospheres of Mars [2],
Jupiter [3], Titan [4], Uranus [5-6], and Neptune [7]. It has been suggested that by 2030 the concentration of C
2
H
2
in the Earth’s atmosphere would reach 150% of its value in the 1990s due to increased use of automobiles worldwide [8]. Consequently, it has been the subject of several high resolution spectroscopic studies, especially on collisional broadening. To our knowledge, no
O
2
-broadening coefficients of C
2
H
2
in the 𝜈
4
+ 𝜈
5
band have been yet reported.
In this work, we have recorded spectra of twenty-one lines belonging to the 𝜈
4
12
C
2
H
2
diluted in O
2
at room temperature.
+ 𝜈
5
band of
Experimental procedure
The measurements have been performed using a high resolution diode-laser spectrometer described in a previous publication from our group [9]. These lines with J values up to 23 were located in spectral range from 1275 to 1380 cm -1 . The samples of acetylene and oxygen were provided by Air Liquide with a stated purity of 99.6, and 99.999%, respectively.
For each studied line, the broadening spectra were recorded at four different pressures of oxygen ranging from 20.00 to 66.21 mbar at room temperature (297.0 ± 1.0 K). The partial pressure of the active gas was chosen depending on each line and its values ranged from 0.01 to 0.10 mbar. The gas mixtures were contained in an absorption cell with an optical path-length of 4.17 m.
The collisional half-widths have been retrieved by fitting individually a theoretical line-shape model on the experimental profile of each line at each pressure. We have fitted by using the usual
Voigt profile [10], but also the models of Rautian [11] and of Galatry [12] which take into account the collisional narrowing due to the molecular confinement (Dicke effect [13]).
The collisional broadening coefficient

0
of a line was the slope of the straight-line derived of a linear regression through the four collisional half-widths (γ
C
− γ
Self
. p
C
2
H
2
) versus pressure of perturber. The self-broadening coefficients of acetylene γ
Self
were obtained from Ref. [14].
Example Spactra
Example of spectra recorded for the P(23) line in the 𝜈
4
+ 𝜈
5
band of C
2
H
2
at room temperature: (1) diode laser emission profile; (2) Doppler line recorded at low absorption and pressure of C
2
H
2
(p=0.0046 mbar) to determine the apparatus function; (3) confocal étalon fringes for relative calibration in wavenumber; (4) 0% transmission level; (5-8) record of the C
2
H
2
line at different pressures of O
2
.

Example of Fitting
Example of theoretical Voigt profile (
●
) fitted to the experimental absorbance α(

)(—) for the P(23) line of C
2
H
2
(0.0747 mbar) diluted into 25.1353 mbar of O
2
. The observed minus calculated residuals, with an intensity scale expanded by 5, are shown at the bottom for the fitted Voigt, Rautian and
Galatry profiles. For clearly, one point out of four has been presented here.
Example of

0
determination
Plot of the collisional half-width γ
C
− γ
Self
. p
C
2
H depends on the O
2
-pressure for the P(23) line
2 broadened by O
2
at 297.75 K. These half-widths are derived from the Voigt (■), Rautian (
●
), and
Galatry (
▲
) profiles. The slopes of best-fit lines, passing through zero, represent the O coefficients

0
. The self-broadening coefficients of C
2
H
2
γ
Self
2
-broadening
were obtained from Lepère et al. [14].

Result
Collisional broadening coefficients γ
0
obtained with the Voigt (■), Rautian (
●
), and Galatry (
▲
) profiles for the C
2
H
2
-O
2
mixtures depend on |𝑚| ( |𝑚| = 𝐽 for P-branch and |𝑚| = 𝐽 + 1 for
R-branch). Experimental errors are estimated to be twice the standard deviation given by the least-squares procedure plus 2% of γ
0
.
Comparision with previous determination
Comparison between our determinations of the collisional broadening coefficient γ
0
, obtained with the the Voigt (■), Rautian (
●
), and Galatry (
▲
) profiles for the C
2
H
2
-O
2 mixtures, and the
O
2
-broadening coefficients of C
2
H
2
of M. Lepère et al.
[15] (▼) calculated for the 𝜈
5
band.
Experimental errors are estimated to be twice the standard deviation given by the least-squares procedure plus 2% of γ
0
.

Conclusion
The O
2
-broadening coefficients of twenty-one absorption lines in the 𝜈
4
+ 𝜈
5
band of acetylene have been firstly measured at room temperature using the Voigt profile as well as the Gautian and
Galatry models which are best in agreement with the experimental profiles. The shape of the curve describing the |𝑚| -dependence of these broadening coefficients is quite the same with that of the theoretical broadening coefficients in the 𝜈
5 temperature [15].
band of acetylene diluted in oxygen at room
References
[1] R.A. Whitby, E.R. Altwicker, Atmos. Environ. 12 , 1289-1296 (1978)
[2] D. Horn, J.M. McAfee, A.M. Winer, K.C. Herr, G.C. Pimentel, Icarus 16 , 543-556 (1972)
[3] P.V. Sada, G.L. Bjoraker, D.E. Jennings, G.H. McCabe, P.N. Romani, Icarus 136 , 192-201 (1998)
[4] R.J Vervark Jr, B.R. Sandel, D.R. Strobel, Icarus 170 , 91-112 (2004)
[5] M. Burgdorf, G. Orton, J. van Cleve, V. Meadows, J. Houck, Icarus 184 , 634-637 (2006)
[6] J. Bishop, K. Atreya, F. Herbert, P. Romani, Icarus 88 , 448-464 (1990)
[7] B. Conrath, F.M. Flasar, R. Hanel, V. Kunde, W. Maguire, J. Pearl, et al. Science 246 , 1454-1459
(1986)
[8] P. Varanasi, L.P. Giver, F.P.J. Valero, J. Quant. Spectrosc. Radiat. Transfer 30 , 505-509 (1983)
[9] L. Fissiaux, G. Blanquet, M. Lepère, J. Quant. Spectrosc. Radiat. Transfer. 113 , 1233-1239
(2012)
[10] B.H. Armstrong, J. Quant. Spectrosc. Radiat. Transfer. 7 , 61-88 (1967)
[11] S.G. Rautian, I.I. Sobel’man, Sov. Phys. Usp. Engl. Transl. 9 , 701-716 (1967)
[12] L. Galatry, Phys. Rev. 122 , 1218-1224 (1960)
[13] R.H. Dicke, Phys. Rev. 89 , 472-473 (1953)
[14] M. Lepère, G. Blanquet, J. Walrand, J.P. Bouanich, M. Herman, J.V. Auwera, J. Mol. Spectrosc.
242 , 25-30 (2007)
[15] D. Lambot, G. Blanquet, J.P. Bouanich, J. Mol. Spectrosc. 136 , 86-92 (1989)