Excitation in an atom refers to the process of raising an electron from a lower energy level to a higher energy level, typically through the absorption of energy.
Collisional excitation is the process of exciting an atom by colliding it with another atom or particle. This collision transfers energy to the atom, causing an electron to move to a higher energy level.
Collisional excitation requires the presence of a high energy collision partner, such as a free electron or another atom, and a close encounter between the two particles. The collision must also have enough energy to transfer to the atom and excite it.
The energy of the collision determines the amount of energy transferred to the atom and thus, the energy level to which the electron is excited. A higher energy collision will result in a greater energy change in the atom.
Some examples of collisional excitation in everyday life include the emission of light by neon signs and the production of light in fluorescent light bulbs. These processes involve the collision of electrons with gas atoms, causing them to become excited and emit light.