So, I am currently doing a course in Molecular Spectroscopy and I am finding some concepts very non-intuitive and very difficult to understand(maybe due to lack of my knowledge or the lack of explanations in the book).
So my problem is as follows- Suppose I have a box full of H-Cl gas molecules and since HCl is a molecule with a non-zero dipole moment, according to the book I am following, the dipole moment component of HCl along some axis changes sinusoidally, just like the time varying electric field of the EM wave which can cause photons to be emitted or absorbed when an EM wave interacts with the molecule. My first question is, how do molecules, which are rotating (or vibrating) really interact with the incoming EM wave and lead to change in energy levels of rotations (or vibrations.)
My second question is that considering HCl as a polar rotating molecule, the charges in the molecule undergo acceleration ( due to rotation) which should lead to charges emitting photons of fixed energies(not releasing a continuum spectrum but emitting photons of discrete energies) and thus molecules should fall to the ground state energy after some time. But this doesn't happen. I didn't understand the answers which my friends gave as they involved some population statistics and quantum particles not radiating energy but they didn't have any backing explanations for them.
I only propose a simple experiment. Suppose I have some HCl gas in an box which is raised to a temperature of 300K. This box is adiabatic so no heat transfers to the surroundings. Now, if the kinetic energy of the molecules is utilised in rotations and vibrations, they should drop down to ground state energy after some time as a result of continuous emission of photons and so all motion should cease after some time. Does this actually happen or am I wrong somewhere?
I am very sorry if the question feels too long. If there is something which needs elaboration, I would surely do that.