# Can an atom have angular momentum? At what angle does an atom reflect a single photon?

Groups of atoms, say two of them, can have angular momentum as a group, but only because they individually have linear momentum and are bound together through a force that causes them to pull on each other so that the group as a whole spins. Does it make sense to talk about the angular momentum of a single atom?

I was trying to understand how a photon's angle of reflection is determined, since there really is no such thing as a continuous surface. There are just groups of atoms. So, what's the difference of the interaction when a photon hits a single atom or hits an atom is surrounded by (8) other atoms in a 2-D arrangement (i.e. a 3x3 grid)?

• See physics.stackexchange.com/q/82464. You cannot usefully model reflection of light by single photons interacting with single atoms. – John Rennie Nov 1 '13 at 14:18
• googling "photon scattering" yields: google.com/… which provides a model for photon scattering – Dave Nov 1 '13 at 14:30
• in the "related questions" is "What does it mean for a particle with no size to have angular momenta [sic]?": physics.stackexchange.com/q/31448 – Dave Nov 1 '13 at 14:32
• What I'm asking is... at a macroscopic level, light is reflected at very specific angles relative to a macroscopic flat surface of atoms. That being the case, whether you call it a photon or a wave, what is the mechanism or what values determine how the light is reflected. A single atom can reflect light. Suppose you shine a laser directly on one atom. Can you describe how the EM field is altered? – Triynko Nov 1 '13 at 15:05
• @Triynko: see en.wikipedia.org/wiki/Thomson_scattering – John Rennie Nov 1 '13 at 15:07