Spectrum of a Gas from Thermal Motion

[Alexander83]

Hi there,
I'm trying to clear up some misconceptions I have about emission spectra from various substances. Most of the discussion about gases focusses on the line emission spectra from a hot, low density gas due to electron shell transitions. But I also know that any charges that are made to accelerate should also give off radiation.

In the simple case of a sample of a monatomic gas, the gas molecules constantly undergo atomic collisions and change directions and would therefore experience intermittent acceleration. Since the atoms themselves contain charges, shouldn't this acceleration cause the gas to give off radiation? If so what would the nature of this radiation be - does it have a formal name and would it have a continuum of frequencies? Is the reason that it is seldom dis

 

[Orodruin]

Since the atoms themselves contain charges, shouldn't this acceleration cause the gas to give off radiation?

While the atoms contain charges, they are overall neutral. Both the positive and negative charges accelerate in the collisions, essentially resulting in a cancellation of the fields.

 

[Alexander83]

Thanks for your reply, Orodruin. So if I understand it, the gas spectrum would then contain *just* discrete emission lines with no continuum components at all? For some reason I had it in my mind that the gas was continuously cooling by emitting radiation, but if I understand what you're saying there should only ever be the line spectrum coming presumably from collisionally-induced excitation of electrons in the atoms?

Alex.