Question on resonant frequency?

[Ralphonsicus]

The question is as follows,

How do you determine the frequency at which different types of molecules resonate to, such as water molecules to microwaves?

 

[f95toli]

You solve the Schroedinger equation for the system. At least this is the basic idea.
In reality this is usually not practical because our computers are not fast enough, so other approximate methods are used instead.

Once you know the energy level spacing you get the frequency of the transition from f=E/h