Photon striking a molecule and getting reflected I am writing a simple simulator which simulate absorption of UV light in solution. The idea is to see if I can see Beer-Lambert laws in my model. It is not intended to be a precise simulator but rather a small educational demo on modeling. 
I have the following problem: I have approximated solvent and solute molecules as sphere. I also assume that UV does not get reflected by solvent molecules therefore solvent molecules are not taking part in any computation in my model.
Now I want to insert a model into my simulator. A photon $P$ strikes a molecule at angle $\theta$ and gets reflected by an angle $\phi$. Is $\phi$ completely dependent on $\theta$ only or there is more complex relation between them? 
I want to keep it quite simple so I am ignoring quantum effects et. al. from my model. 
 A: One cannot ignore quantum mechanics when one is talking of photons. Photons, in addition to giving rise to transitions of bound states or being emitted by changes in energy levels of bound states ( atom, molecule,lattice) can also interact elastically with electrons and the fields that collectively build up around matter.
Now a liquid which has a solute and a solvent may have various behaviors. Take salt in water. The fact that we do see inside the water if we shine a light to it, with small color distortions, means that the photons arriving in our eyes have back scattered elastically. Whether it hits a water molecule or a salt one does not play a role in this.Depending on the liquid and the solvent though changes in color would imply a sequence of absorption and re-emission as John explains, a quantum mechanical mechanism.
All in all , interactions that discriminate between solvent and solute will need sequential absorption and re-emission modeling. You cannot ignore quantum mechanics if you are talking of photons.
A: Photons do not get reflected from molecules in a solvent.
Typically a photon will be absorbed and will excite one of the electrons in the molecule into a higher energy state. In a liquid this energy is usually transferred to other molecules by collisisons, so no photon is re-emitted. The result is that the absorbed photon just disappears.
There are situations in which photons are re-emitted, for example in fluorescence, but this is the sort of thing you would on;y build into your model at a later stage.
