Re: Can mechanical vibration reduce temp. by countering molec. vibration?

Good idea, but not quite...

It turns out that molecular vibrations are very, very high frequency -- 
something in the terahertz range -- so that it's not possible for 
mechanical vibrations to provide phased (or dephased) compensation for 
motion to heat or cool a material.

On the other hand, because this frequency corresponds to frequencies 
accessible with lasers, they can be used to do this -- but only to a 
point.  Like all harmonic oscillators that exist in the quantum mechanical 
world, most all molecules have some lower level non-zero energy that you 
just can't go below.  In fact, the stimulated emission process which 
allows lasers to exhibit optical gain does just the sort of upper level 
depopulation you describe, but you still don't get down to zero energy.  
You can absorb laser light to increase the excitation level, but depending 
on how the vibrational excitation couples to the kinetic energy of the 
molecule as a whole it's not clear how effectively you might heat the 
gas.  Some gases prefer to radiate the energy away, so that not much 
heating would actually occur.

Thanks for the interesting question!