Kayser (K) (2) : A unit of energy used in atomic and molecular physics. Since the frequency of a photon is proportional to the energy it carries, the kayser is also equivalent to an energy of 123.984 microelectronvolt
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}