To answer it, we need to know:

* Which enzyme are we talking about? Enzymes have specific functions, and the molecule they store an excited particle in depends on the enzyme's purpose.

* What is the "excited particle"? Is it an electron, a proton, a photon, or something else?

* What is the reaction or process taking place?

For example, if the excited particle is an electron, the enzyme might store it in a coenzyme such as NADH or FADH2. If the excited particle is a photon, it could be stored as chemical energy in a molecule like glucose.

Please provide more details so I can give you a more accurate answer.