The Effects of Permanent Dipole Moments in Lasermolecule interactions
Back to Top
Details to be posted shortly.
Collisioninduced Absorption
Back to Top
It is wellknown that homonuclear diatomic molecules (e.g. N_{2} or
O_{2}) do not have permanent dipole moments in the ground electronic
state. Therefore, the gas does not exhibit vibrationrotational absorption in
the infrared region as heteropolar diatomics do. However, there are weak
continuumtype transitions due to translational, rotational, and vibration
rotational transitions caused by transient dipoles that are induced during
binary collisions. The latter is generally called collisioninduced 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 O_{2} and N_{2}
for N_{2}N_{2}, O_{2}O_{2},
O_{2}N_{2}, and N_{2}O_{2} 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 LennardJones potential.
Using the LJ potential and the multipoleinduced 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 N_{2}, the
fundamental band has been computed from 21002600 cm^{1} and
for O_{2}, the fundamental has been computed from
13001800 cm^{1}. The spectrum has been computed every 5
cm^{1} within these energy ranges.
Energies (in cm^{1}) used in all calculations.
Parameter 
N_{2} 
O_{2} 
w_{01} 
2329.914 
1556.385 
B_{v=0} 
1.989581 
1.4297116 
D_{v=0} 
5.76x10^{6} 
4.839x10^{6} 
B_{v=1} 
1.972263 
1.4137816 
D_{v=1} 
5.76x10^{6} 
4.839x10^{6} 
The data is available in two formats:
 A single ascii file containing all temperatures within the
range T = 190  310K
 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.
N_{2}N_{2}
Reference: J. Boissoles, R.H. Tipping, and C.Boulet, "Theoretical study of collisioninduced
fundamental absorption spectra of N_{2}N_{2} pairs for temperatures
between 77 and 297K", Journal of Quantitative Spectroscopy and Radiative Transfer
51, 615 (1994).
Parameter 
Value 
a_{00} 
11.74 
a_{01} 
0.365 
g_{00} 
4.75 
g_{01} 
0.438 
Q_{00} 
1.052 
Q_{01} 
0.0563 
f_{00} 
7.5 
f_{01} 
0.15 
s 
6.956 
E 
91.5 


O_{2}O_{2}
Reference: G. Moreau, J. Boissoles, C. Boulet, R.H. Tipping, and Q. Ma,
"Theoretical study of collisioninduced
fundamental absorption spectra of O_{2}O_{2} pairs for temperatures
between 193 and 297K", Journal of Quantitative Spectroscopy and Radiative Transfer
64, 87 (2000).
Parameter 
Value 
a_{00} 
10.87 
a_{01} 
0.357 
g_{00} 
7.30 
g_{01} 
0.57 
Q_{00} 
0.264 
Q_{01} 
0.106 
f_{00} 
4.4 
f_{01} 
0.185 
s 
6.55 
E 
106.7 


NOTE:
The O_{2}O_{2} calculation
includes a shortrange
contribution for the L = 3 mechanism of the form m
_{3}exp[(R  s)/(0.11s)]
where m_{3} = 5.0x10^{5}.
O_{2}N_{2}
and N_{2}O_{2}
Reference: G. Moreau, J. Boissoles, R. Le Doucen,C. Boulet, R.H. Tipping, and Q. Ma,
"Experimental and theoretical study of the collisioninduced
fundamental absorption spectra of N_{2}O_{2} and
O_{2}N_{2}", Journal of Quantitative Spectroscopy and Radiative Transfer
69, 245256 (2001).
Parameter 
N_{2} Value 
O_{2} Value 
a_{00} 
11.50 
11.08 
a_{01} 
0.365 
0.357 
g_{00} 
4.75 
7.30 
g_{01} 
0.438 
0.570 
Q_{00} 
1.052 
0.264 
Q_{01} 
0.0613 
0.1028 
f_{00} 
7.5 
4.4 
f_{01} 
0.15 
0.185 
s 
6.72 
E 
107.125 


NOTE:
The O_{2}N_{2} calculation
includes a shortrange
contribution for the L = 3 mechanism of the form m
_{3}exp[(R  s)/(0.11s)]
where m_{3} = 4.5x10^{5}.



NOTE:
The N_{2}O_{2} calculation
includes a shortrange
contribution for the L = 3 mechanism of the form m
_{3}exp[(R  s)/(0.11s)]
where m_{3} = 5.0x10^{5}.

