The life of π and σ - A tutorial review of the ubiquitous use of these symbols in Zeeman and magnetic-resonance spectroscopy

Abstract

Certain concepts and symbolism as applied to electromagnetic radiation and especially the concept of photons are discussed and (perhaps) clarified. A useful summary of the properties of photons is provided, and the concept of polarization is discussed. In particular, the common usage in Zeeman and magnetic-resonance (EPR and NMR) spectroscopy of the symbols π and σ is examined herein, both from the historical viewpoint and the scientific standpoint, and certain errors and fallacies are brought to attention. Brief reference to relevant recent work published on dynamic nuclear polarization and on pulse EPR is included. © 2008 Wiley Periodicals, Inc.