Introduction to Excited State
After the atoms or molecules absorb a certain amount of energy, the electrons are excited to a higher energy level but not yet ionized. The excited state generally refers to the electronic excited state. When the gas is heated, the molecular kinetic energy increases, and when the liquid and solid are heated, the molecular vibration energy increases, but no electrons are excited. These states are not excited states. When atoms or molecules are in an excited state, the distribution of the electron cloud will undergo some changes, the distance between the equilibrium nucleuses of the molecule will increase slightly, and the chemical reaction activity will increase. All photochemical reactions are chemical reactions that are carried out after molecules are promoted to an excited state, so photochemistry is also called excited state chemistry. When ionizing radiation (or electromagnetic radiation) interacts with matter, when the energy transferred to the atom or molecule is lower than its ionization potential and sufficient to cause the electron to transition to a higher energy level, the atom or molecule is in an excited state. The excited state and the ground state have different potential energy curves and equilibrium nuclear spacing.