Ultraviolet radiation, particularly from hot stars, is the main driver of ionization in the interstellar medium, as it has sufficient energy to remove electrons from atoms and molecules.

Photodissociation, the breaking of chemical bonds due to the absorption of radiation, is the primary mechanism by which radiation initiates chemical reactions in the interstellar medium.

Hydrogen molecules (H2) are the most abundant molecules in the universe and are primarily formed through radiative association reactions between hydrogen atoms in the interstellar medium.

Cosmic rays, high-energy particles from outside the solar system, play a multifaceted role in astrochemistry, including initiating chemical reactions, providing energy for endothermic reactions, and contributing to the formation of complex organic molecules.

Photoexcitation, the absorption of radiation by a molecule resulting in the promotion of an electron to a higher energy level, is the primary process responsible for the formation of polycyclic aromatic hydrocarbons (PAHs) in the interstellar medium.

Dust grains, small solid particles in the interstellar medium, are the primary source of infrared radiation, as they absorb and re-emit starlight in the infrared wavelength range.

Photodissociation of water molecules (H2O) by ultraviolet radiation is the primary process responsible for the formation of water ice in molecular clouds, as it leads to the formation of hydroxyl radicals (OH) and hydrogen atoms (H), which can then recombine to form water ice.

X-ray radiation, high-energy photons with wavelengths shorter than ultraviolet radiation, plays a similar role to cosmic rays in astrochemistry, initiating chemical reactions, providing energy for endothermic reactions, and contributing to the formation of complex organic molecules.

Photodissociation of carbon dioxide (CO2) by ultraviolet radiation is the primary process responsible for the formation of carbon monoxide (CO) in the interstellar medium.

Photodissociation, the breaking of chemical bonds due to the absorption of radiation, is the primary mechanism by which radiation drives chemical reactions in the interstellar medium.

Ultraviolet radiation, particularly from hot stars, is responsible for the formation of formaldehyde (H2CO) in the interstellar medium through the photodissociation of water molecules (H2O) and the subsequent reaction of hydroxyl radicals (OH) with carbon monoxide (CO).

Cosmic rays, high-energy particles from outside the solar system, are the primary source of gamma-ray radiation in the interstellar medium, as they interact with interstellar gas and dust, producing gamma rays through various processes.

Photodissociation of hydrogen isocyanide (HNC) by ultraviolet radiation is the primary process responsible for the formation of hydrogen cyanide (HCN) in the interstellar medium.

Infrared radiation plays a limited role in initiating chemical reactions directly, but it is important in providing a source of energy for endothermic reactions, which are reactions that require an input of energy to proceed.

Photodissociation of formaldehyde (H2CO) by ultraviolet radiation is the primary process responsible for the formation of methanol (CH3OH) in the interstellar medium.