The process by which a particle or a set of particles crosses a barrier on its @P04780@ without having the energy required to surmount this barrier. Since the rate of tunnelling decreases with increasing @R05214@, it is significant in the context of isotope effects of hydrogen @I03331@.
PAC, 1994, 66, 1077. (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1174 [Terms] [Paper]
See also:
PAC, 1996, 68, 2223. (Glossary of terms used in photochemistry (IUPAC Recommendations 1996)) on page 2282 [Terms] [Paper]