photon

Particle of zero charge, zero rest mass, spin quantum number 1, energy $Math - ei$ and momentum $Math - ei$ ( $Math - symbol$ is the Planck constant, $Math - symbol$ the frequency of radiation and $Math - symbol$ the speed of light), carrier of electromagnetic force.

Source:

Green Book, p. 93

PAC, 1996, 68, 2223 (Glossary of terms used in photochemistry (IUPAC Recommendations 1996)) on page 2262