Theory of the Fireball

N, and 0. The Schumann-Runge bands start from the electronic ground state
of 02, hence are available at law T; at higher T, the spectral region of
strong absorption spreads due to excitation of vibrational states; but at
still higher T, oxygen dissociates and therefore the bands die out (at
&looo, they contribute less than lO$ of the absorption). The photo-
electric absorption in N and 0 requires not only the presence of these
atoms but also their electronic excitation, and therefore does not become
importast until about 10,OOOo.
Table VI1 gives, for density p = O.lpO, the spectral regions of
strong absorption. In accord with Sec. 3b, we define this by p > lom3
(mean free path less than 10 meters) or I-L > lom2 (4 1 meter). The
table shows that strong absorption covers a particularly wide spectral
region at 4000°, shrinking substantially at 6000~. Very strong absorption,
p > LOm2 m-', occurs in quite a lwge spectral. region for T = 4000° but
shrinks to practically nothing at 6000~ and to nothing at 8000°. At
12,000°, very strong absorption occurs again but is now in the visible.
The strong absorption in the ultraviolet (hv > 3.5 w) means first
of all that the W is not emitted to large distances and can therefore
0
not be observed; e.g., at T = 4000 and hv = 3.5 ev, we have
%e should also add the photoelectric absorption from excited states of
NO, which should be especially noticeable at 8000°.
41
JC.