photon

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

Source:

Green Book, 2nd ed., p. 93

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