Photochemistry
Reaction Pathways
A photochemical process may be considered to consist of two steps: the absorption of a photon, followed by reaction. If the absorption of a photon causes an electron within an atom or molecule to increase its energy, the species is said to be electronically excited. The absorption and reaction steps for a molecule AB may be written as: AB + hν → AB* AB* → products where hν represents the energy of a photon of frequency ν and the asterisk indicates that the species has become electronically excited. The excited species, AB*, has the additional energy of the absorbed photon and will react in order to reduce its energy. Although the excited species generally does not live long, it is sometimes formally indicated when writing photochemical reactions to stress that the reactant is an electronically excited species. The possible reactions that an electronically excited species may undergo are illustrated below. Note: the symbols * and † denote different levels of electronic excitation.
Absorption of a photon (electronic excitation)
Followed by:
| i) | AB* → A + B | Dissociation |
| ii) | AB* → AB+ + e– | Ionization |
| iii) | AB* → BA | Isomerization |
| iv) | AB* + C → AC + B or ABC | Reaction |
| v) | AB* + DE → AB + DE* | Energy Transfer (intermolecular) |
| vi) | AB* + M → AB + M | Physical Quenching |
| vii) | AB* → AB† | Energy Transfer (intramolecular) |
| viii) | AB* → AB + hν | Luminsecence |
Additional topics
- Photochemistry - Dissociation
- Photochemistry - Photochemistry Induced By Visible And Ultraviolet Light
- Other Free Encyclopedias
Science EncyclopediaScience & Philosophy: Philosophy of Mind - Early Ideas to Planck lengthPhotochemistry - The Basic Laws Of Photochemistry, Photochemistry Induced By Visible And Ultraviolet Light, Reaction Pathways, Dissociation - Ionization, Isomerization