Hello Herman!

07 May 05 22:28, Herman Trivilino wrote to Gerrit Kuehn:


 GK>> It's as well a measure of energy as eV or Hz are. They're all
 GK>> called "energy equivalents" and are valid in their context.
 GK>> Have a look at
 GK>> http://physics.nist.gov/cuu/Constants/factors.html

 HT> I see that they do indeed list a conversion between inverse meters 
 HT> and joules, so I guess I'll have to stand corrected.  I don't like 
 HT> it, though.  It's sloppy.  It's possible to have several different 
 HT> waves, all with the same wavenumber, and each having a different 
 HT> energy.

I know. I guess it's really a /very/ traditional thing among spectroscopy
people. Energies of atomic levels are measured in cm^-1, I've hardly seen
anything else (eV or Ry sometimes). The unit is really convenient as it
produces easy-to-handle numbers. Typical atomic energy levels range from 0
to some 10^5 cm^-1, an eV is worth 11600cm^-1 (10000 for quick
calculations) and if you need a temperature it's 1.436K (or 1.5, if you
don't have a calculator at hand).

 HT>>> I know for a fact that researchers who routinely work in
 HT>>> units of wavenumbers THINK of the wavenumber as an indicator
 HT>>> of the amount of energy.  They can get away with that
 HT>>> because it works for them in that one specialized area.
 HT>>> When these researchers publish their work, they do not use
 HT>>> the wavenumber as a measure of energy.

 GK>> Well, I don't know from where you get your facts.

 HT> When I worked in solid state physics (as a grad student) we routinely 
 HT> used the cm^-1, but I don't recall ever having seen it referred to as 
 HT> a unit of energy.

Well, as I said before, it's typical for optical spectroscopy. I guess
solid state physics is as far away from this as anything in physics an be.
;)

 HT> Nowadays, though, I read journals like TPT, AJP, and Physics Today.  

Sounds like you're working as a teacher. The articles on my desk here that
are using this unit are from Phys.Rev.A, J.Phys.Chem.Ref.Data and J.Phys.D.

 HT> None of them ever refer to the wave number as a measure of energy, at 
 HT> least as far as I can recall.  Certainly none of the the introductory 
 HT> physics textbooks do it, either.

I always had difficulties to understand what a /textbook/ in English
speaking countries really is. There is a faint memory that it had something
to do with the "audience". Textbooks are for undergraduate
students, or something like that?
However this may be, for anyone interested in spectroscopy I can recommend
the following book (which -of course- uses cm^-1 for energies :-):

A. Thorne, U. Litzen, S. Johansson
Spectrophysics - Principles and Applications
Springer-Verlag Berlin Heidelberg New York (1999)
ISBN 3-540-65117-9

 HT> As I said, though, usage differs in specialized areas.

Which is certainly true. This was the reason why I suggested in the first
place that measuring potential energies in V may be alright in some areas.


Regards,
Gerrit

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