Quantities, Symbols, and Units in Spectroscopy

Dec 01, 2012

The two international governing bodies that impact spectroscopy are the International Union of Pure and Applied Physics (IUPAP) and the International Union of Pure and Applied Chemistry (IUPAC). In this installment, we take a look at the various terms that have come out of these bodies. Spectroscopists are probably well aware of these naming conventions, but this column can serve as a reminder of what certain terms mean and how they should be properly used in scientific work.

The two international governing bodies that impact spectroscopy are the International Union of Pure and Applied Physics (IUPAP) and the International Union of Pure and Applied Chemistry (IUPAC). IUPAP was organized in 1922 and began meeting to formalize physics standards worldwide the next year. It is organized into commissions, and one that concerns us here is the Commission on Symbols, Units, Nomenclature, Atomic Masses & Fundamental Constants (SUNAMCO). IUPAC was formed in 1918, but actually has its roots in a meeting in 1860 organized by Kekulé (of benzene fame) that was held to standardize organic chemical nomenclature. The efforts of IUPAC's Interdivisional Committee on Terminology (ICTNS) concern us here.


Table I: General quantities
In this installment, we consider the conventions. I do not mean the gatherings of people in hotels or meeting centers to meet and exchange information, but rather the agreed-upon quantities, symbols, and units that experts in a field use to communicate their ideas.


Table II: Quantities relating to electromagnetic radiation
Let's be honest, some conventions are arbitrary and whimsical (remember the story of the unit "barn" for nuclear cross sections?). Some conventions become issues of national pride (think: naming new chemical elements) while some have little provenance other than long-term historical use (think: candela). But understanding and using the proper conventions is fundamentally important to properly communicating ideas, especially technical ideas like spectroscopy. That is one reason that instruction in proper conventions is a crucial part of educating new scientists and technicians.


Table III: General spectroscopic quantities
All fields have conventions. For example, what is a language but an agreed-upon convention for making sounds? Postal delivery may not seem like a highfalutin' profession, but there are conventions to writing and interpreting delivery addresses that must be mastered to be a competent postal delivery person. Here, we will review some of the conventions for the quantities that are used in spectroscopy, along with their units and the occasional definition.