Which method does NOT excite atoms?

The method that does not excite atoms is the reduction of pressure. When pressure is reduced in a gas, it typically leads to increased distances between atoms or molecules and can result in fewer collisions among them. Excitation involves raising an atom to a higher energy state, which usually requires energy input through various means.

In contrast, applying a potential difference can cause charged particles to gain energy and accelerate, leading to potential excitation of atoms when they collide with them. Similarly, collisions with high-energy particles can impart energy to atoms directly, resulting in excitation. Absorption of photons also excites atoms when the energy from the photons is absorbed, promoting electrons to higher energy levels. Reduction of pressure, however, does not provide energy to excite particles; instead, it creates conditions that might prevent atoms from interacting with one another effectively.