Photosynthesis is much, much more complicated than that. It is not about just water and carbon dioxide, there is a huge system of molecules and enzymes at work. Whole process takes many steps, most of them not utilizing directly energy from the Sun. Most of these steps can be at least partially explained in terms of collision theory, but collision theory is a highly simplified model, that doesn't account for many phenomena present in photosynthesis process chemistry.
You are right that at night photosynthesis stops.