What Forces Cause Rotational Emissions?

[Gnomie27]

I was curious about what forces can be applied to a molecule to cause a rotational emission.

 

[Chandra Prayaga]

What is a rotational emission?

 

[Gnomie27]

Essentially, rotational emission is caused when there is a change in a molecules spin state to a lower energy, the difference is released in the form of a low energy photon (somewhere around micro and radio frequencies). Its similar to vibrational emissions, but those release infrared, both behaviors a governed by QM though. Its used in astronomy and a few forms of microscopy.
(I am a little shaky on the specifics myself. If someone has a better explanation or more to offer, its always appreciated!)

So to be more specific, I am wondering what methods can be implemented to lower a molecules spin state on demand, so that it results in an emission.
Are there protocols for using magnets, or changes in voltage, etc. , that can cause such an effect?