(a) Distinguish between photodissociation and photoionization.

Key Concepts

Photodissociation

Photodissociation is a process in which a molecule absorbs light energy and breaks apart into two or more smaller fragments, typically atoms or smaller molecules. This occurs when the energy of the absorbed photon exceeds the bond dissociation energy of the molecule, leading to the breaking of chemical bonds. An example is the dissociation of ozone (O3) into oxygen molecules (O2) and oxygen atoms (O) upon exposure to ultraviolet light.

Photoionization

Photoionization is the process by which an atom or molecule absorbs a photon and subsequently loses one or more electrons, resulting in the formation of a positively charged ion. This process requires that the energy of the incoming photon be greater than the ionization energy of the atom or molecule. A common example is the ionization of sodium (Na) when it absorbs ultraviolet light, leading to the formation of Na+ ions.

Energy Considerations

Both photodissociation and photoionization are governed by energy considerations, specifically the relationship between the energy of the absorbed photon and the energy required to break bonds or remove electrons. In photodissociation, the photon energy must exceed the bond dissociation energy, while in photoionization, it must exceed the ionization energy. Understanding these energy thresholds is crucial for predicting the outcomes of light-matter interactions in chemical processes.