Photon's change of direction of propagation

[Goodver]

Photons propagate in a certain direction. When it encounters an atom on its way, and an energy of photon is equal to the energy difference between some levels in the atom photon can be absorbed.

But, what happens if an energy of the photon does not match energy difference between levels in the atom. Since atom is "on the way" of photon propagation. How photon will behave in this way? Will the vector of propagation be changed? If yes, on which angle will it deviate? And what makes it to deviate? Or the direction of the photon will stay unchanged?

 

[WannabeNewton]

How photon will behave in this way? Will the vector of propagation be changed? If yes, on which angle will it deviate? And what makes it to deviate? Or the direction of the photon will stay unchanged?

It will get scattered by the atomic electrons into some solid angle in some direction at an angle relative to the original propagation direction with some wave vector given by the differential scattering cross section for the interaction. The out-state will be given probabilistically based upon the in-state. In this particular case one can look at Compton scattering: http://en.wikipedia.org/wiki/Klein–Nishina_formula