Photon Absorption

[americanforest]

If a photon does not have the required energy for changing the quantum state of a particle/atom/molecule, is it absorbed and instantaneously re-emitted with the same energy when it arrives at said particle/atom/molecule or is it not absorbed at all?

Also, does it make any difference in measurements of such interactions?

[nandan]

to understand this concept better try looking at it from a wave point of view.
if the diff b/w the two energy levels is such that the wave's freq. does not match that
of the energy separation in freq. units there will be no resonance and there will be no absorption.

[Claude Bile]

The photon is not absorbed at all.

I don't understand the second part of your question.

Claude.