Thermal radiation and optical opacity

Chalky

Thermal radiation and optical opacity

The (apparently) prevailing belief at sci.astro.research, that matter
cannot radiate heat unless it is optically opaque at the appropriate
EM frequencies, has led me to ponder whether this is true or not, and
why.

At one level, it doesn't seem to make sense, because if the matter in
the middle of a cloud of gas radiates thermally, the matter around it
would need to be transparent, not opaque, at such frequencies, for the
radiation to get out. Opaqueness would merely result in a larger
temperature gradient and, thus, both less energy radiated to the
outside overall, and less cooling.

If we consider the situation at the inter-molecular level, where the
heat is expressed as random motions of the molecules, and random
changes in motion during resultant collisions between molecules, I
don't see how those molecules could fail to radiate during collisions.
My reasoning for concluding thus is as follows. The reason for such
changes in motion is electrical repulsion between the electron clouds
of the colliding molecules, resulting in accelerations proportional to
charge divided by electron mass. The corresponding smaller
accelerations of the nuclei, however, should be proportional to charge
divided by nuclear mass, thus resulting in substantial deformations of
the molecules during collisions, in turn resulting in substantially
changing dipole moments, which cannot fail to radiate
electromagnetically.

I would appreciate objective comments from physicists on this matter,
since the opposing (prevailing) belief appears to be quite entrenched
within the astrophysics community, and well supported by astrophysics
textbooks.

Chalky
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