A unit of energy used in atomic and molecular physics, equal to about 2.1799 x 10-18 joule or 13.60569 electronvolts. The rydberg is also equal to exactly 0.5 hartree
Russ Rowlett (Director), How Many? A Dictionary of Units of Measurement, Center for Mathematics and Science Education University of North Carolina, USA 2005. http://www.unc.edu/~rowlett/units/dictA.html, (Unit of Meas and Covr Factors - Amer) {608}