• The effects of permanent dipole moments in laser-molecule interactions

• Collision-induced Absorption

Details to be posted shortly.

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It is well-known that homonuclear diatomic molecules (e.g. N₂ or O₂) do not have permanent dipole moments in the ground electronic state. Therefore, the gas does not exhibit vibration-rotational absorption in the infra-red region as hetero-polar diatomics do. However, there are weak continuum-type transitions due to translational, rotational, and vibration- rotational transitions caused by transient dipoles that are induced during binary collisions. The latter is generally called collision-induced absorption (CIA) or supermolecular absorption. The understanding of CIA is important for the study of radiative transfer in the Earth's atmosphere.

The CIA has been determined for O₂ and N₂ for N₂-N₂, O₂-O₂, O₂-N₂, and N₂-O₂ pairs where in each instance the first molecule listed in assumed to make the fundamental transition. For each of these dimers, the isotropic interaction (anisotropy is ignored) is modeled by a Lennard-Jones potential. Using the LJ potential and the multipole-induced dipole functions, the collisioninduced absorption can be determined. Please see the listed references for a complete discussion of the theory.

Below we have illustrative plots for T = 200K, 250K and 300K. More importantly, we make available data for the absorption coefficient (in units of cm^-1 amagat^-2) for these various pairs over a wide temperature range. The spectra have been computed every 10 K from 190 - 310 K.

For N₂, the fundamental band has been computed from 2100-2600 cm^-1 and for O₂, the fundamental has been computed from 1300-1800 cm^-1. The spectrum has been computed every 5 cm^-1 within these energy ranges.

The data is available in two formats:

1. A single ascii file containing all temperatures within the range T = 190 - 310K
   
2. A gzipped and tarred file, which upon expansion gives a series of files where each file contains the absorption at a single temperature

Currently, these are the only results we have available. If there are any other species that you are interested in, please feel free to contact us as we may be able to help. Write to Professor R.H. Tipping or Dr. A. Brown and we will try to get back to you as soon as possible.

N₂-N₂
Reference: J. Boissoles, R.H. Tipping, and C.Boulet, "Theoretical study of collision-induced fundamental absorption spectra of N₂-N₂ pairs for temperatures between 77 and 297K", Journal of Quantitative Spectroscopy and Radiative Transfer 51, 615 (1994).

Parameter Value a00 11.74 a01 0.365 g00 4.75 g01 0.438 Q00 -1.052 Q01 0.0563 f00 -7.5 f01 -0.15 s 6.956 E 91.5

Data
ASCII text file	specn2n2.out
tarred and gzipped text files	specn2n2.tar.gz

O₂-O₂
Reference: G. Moreau, J. Boissoles, C. Boulet, R.H. Tipping, and Q. Ma, "Theoretical study of collision-induced fundamental absorption spectra of O₂-O₂ pairs for temperatures between 193 and 297K", Journal of Quantitative Spectroscopy and Radiative Transfer 64, 87 (2000).

Parameter Value a00 10.87 a01 0.357 g00 7.30 g01 0.57 Q00 -0.264 Q01 0.106 f00 4.4 f01 0.185 s 6.55 E 106.7

NOTE: The O₂-O₂ calculation includes a short-range contribution for the L = 3 mechanism of the form m ₃exp[-(R - s)/(0.11s)] where m₃ = 5.0x10^-5.

Data
ASCII text file	speco2o2.out
tarred and gzipped text files	speco2o2.tar.gz

O₂-N₂ and N₂-O₂
Reference: G. Moreau, J. Boissoles, R. Le Doucen,C. Boulet, R.H. Tipping, and Q. Ma, "Experimental and theoretical study of the collision-induced fundamental absorption spectra of N₂-O₂ and O₂-N₂", Journal of Quantitative Spectroscopy and Radiative Transfer 69, 245-256 (2001).

Parameter N2 Value O2 Value a00 11.50 11.08 a01 0.365 0.357 g00 4.75 7.30 g01 0.438 0.570 Q00 -1.052 -0.264 Q01 0.0613 0.1028 f00 -7.5 4.4 f01 -0.15 0.185 s 6.72 E 107.125
NOTE: The O2-N2 calculation includes a short-range contribution for the L = 3 mechanism of the form m 3exp[-(R - s)/(0.11s)] where m3 = -4.5x10-5.
NOTE: The N2-O2 calculation includes a short-range contribution for the L = 3 mechanism of the form m 3exp[-(R - s)/(0.11s)] where m3 = -5.0x10-5.

Data
ASCII text file	speco2n2.out	specn2o2.out
tarred and gzipped text files	speco2n2.tar.gz	specn2o2.tar.gz

Translation-rotation correction factor
Reference: J. Boissoles, C. Boulet, R.H. Tipping, A. Brown, and Q. Ma, "Theoretical calculation of the translation-rotation collision-induced absorption in N₂-N₂, O₂-O₂, and and N₂-O₂ pairs", Journal of Quantitative Spectroscopy and Radiative Transfer 82505-516 (2003). .

The correction factor R(w,T) as a function of energy in cm-1.

Data
ASCII text file	rwT.dat

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