Photodissociation is the process by which molecules are broken apart by the absorption of ultraviolet radiation.

Oxygen (O2) is the primary absorber of ultraviolet radiation in the mesosphere.

The D region is the layer within the mesosphere where the majority of photodissociation occurs.

Photodissociation in the mesosphere produces oxygen atoms (O), nitrogen atoms (N), and hydrogen atoms (H).

The primary chemical reaction that occurs between oxygen atoms and molecular oxygen in the mesosphere is recombination, which forms ozone (O3).

The primary chemical reaction that occurs between nitrogen atoms and molecular nitrogen in the mesosphere is recombination, which forms molecular nitrogen (N2).

The primary chemical reaction that occurs between hydrogen atoms and molecular hydrogen in the mesosphere is recombination, which forms molecular hydrogen (H2).

The primary chemical reaction that occurs between ozone and molecular oxygen in the mesosphere is dissociation, which forms oxygen atoms (O) and molecular oxygen (O2).

The primary chemical reaction that occurs between ozone and nitrogen atoms in the mesosphere is dissociation, which forms nitrogen monoxide (NO) and oxygen atoms (O).

The primary chemical reaction that occurs between ozone and hydrogen atoms in the mesosphere is dissociation, which forms hydroxyl radicals (OH) and oxygen atoms (O).

The primary chemical reaction that occurs between nitrogen monoxide and molecular oxygen in the mesosphere is recombination, which forms nitrogen dioxide (NO2).

The primary chemical reaction that occurs between nitrogen dioxide and molecular oxygen in the mesosphere is dissociation, which forms nitrogen monoxide (NO) and oxygen atoms (O).

The primary chemical reaction that occurs between hydroxyl radicals and molecular oxygen in the mesosphere is recombination, which forms hydrogen peroxide (H2O2).

The primary chemical reaction that occurs between hydrogen peroxide and molecular oxygen in the mesosphere is dissociation, which forms hydroxyl radicals (OH) and oxygen atoms (O).

The primary chemical reaction that occurs between methane and hydroxyl radicals in the mesosphere is dissociation, which forms methyl radicals (CH3) and water vapor (H2O).