Theory of the Fireball

4. ABSORPTION coEFF1c1ms
a. Infrared / / .
The main absorption in the infrared is due to free-free electron
transitions. These are treated incorrectly in the paper by Meyerott et
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al., in whicn it is assumed that such transitions occur only in the
field of ions. At. tke important temperatures of 8000' or less, the degree
of ionization is or less. Therefore, the free-free transitions in
the field of neutral atoms and molecules are much more important than
those in the field of ions, even though each individual atom contributes
far less than each ion.
The effectiveness of neutrals in inducing free-free transitions has
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been measured and interpreted by Taylor and Kivel at
laboratory. As compared to one' ion, the effectiveness
tant neutral species is
N2 : 2.2 f 0.3 X
N: 0.9 f 0.h x lo-=!
0: Oe2 f 0.3 X lo-=!
the Avco-Everett
of the most impor-
Thus nitrogen gives about the same contribution wnether molecular or
atomic, and the contribution of oxygen is very small. As a result, one
atom of air is equivalent to about a = 0.8 X ion (of unit charge).
The free-free absorption coefficient in cm'l is then
cLf f
= 0.87 x 10 (%) 2(e-)(hv)-3
= 7.0 T '-I/* (b) 2( e-) (hv) -3
1
I