Theory of the Fireball

The concentration of all the absorbing species depends strongly on
temperature: The N first positive absorption starts from the electronic
2
level A, which has an excitation energy of 5.7 ev; NO itself requires
high temperature for its formation; and N2 and 0- are ions whose concen-
tration behaves like the electron concentration, discussed above in
See. 4a. Therefore, the absorption depends strongly on temperature.
first positive is the most important absorber, and its temperature depend-
ence (relative to the ground state of N2) is about
5.7 ev (- KT )
The concentration of N~ up to 6000' is nearly independent of density,
but at 80Wo it is about proportional to p1l2 (per air atom) so that near
"N2 -
3/2 ,8
which is nearly the same dependence as derived in ( 4.4) for the free -f ree
transitions. In terms of pressure we get
Table V gives the absorption coefficients for four temperatures,
three densities, and -six wave lengths. In the visible (1-1/8 to 2-5/8 ev)
the strong increase in absorption with temperature is evident, a factor
I 37
+
N2
, .