Talk:Saha ionization equation

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Units[edit]

can someone tell me what the exact units of the individual variables should be? as we all know there are many different forms, different units, for the variables. thank you.

I will fix the equations so its clear what each variable means, but its not necessary to specify the exact units of each variable as long as they are consistent. For example, the electron mass is in units of mass, and we might choose the MKS system of units, in which case the mass would be kilograms. Or we could choose the CGS system of units, in which case the mass would be in grams. The equation is true in either system, so we don't need to specify which system, all we need to do is to say the electron mass is in units of mass, which is pretty obvious, so thats not even needed either. PAR 22:06, 12 August 2005 (UTC)[reply]

Ionization energy[edit]

The definition of epsilon_i says it is "the energy required to remove an electron from an (i-1)-level ion, creating an i-level ion", but the usage in the equation is that of the total ionization energy of state i, since the equation should have the energy to go from state i-1 to state i (or, as written in the equation, from state i to state i+1), and that is written explicitly as an energy for state i+1 minus the energy for state i.

Please correct me if I'm wrong, but I think that either the "- epsilon_i" should be removed from the exponential argument in the equation, or else epsilon_i should be defined as the total ionization energy above the neutral state.

Sorry for any clumsiness in submitting this comment; I have not done it before, and I don't want to attempt to edit the page myself.

Incidentally, the Saha equation can be put into a form completely analogous to the Boltzmann equation for the distribution over excitation states, i.e., the ratio of the fraction in a given state to the total, rather than the fraction relative to the next lower state. This form is both faster to compute and more accurate than the form relating consecutive states and eliminates the need to compute a "dominant potential" estimate for the most populated state (i.e., to avoid computing the ratio for states in which the denominator is essentially zero). I published the derivation in 1970 as a graduate student in a little short-lived backwater journal named the "Maryland Astronomical Journal", to which all grad students were strongly requested to contribute. Although I received several reprint requests, the improved form did not achieve traction, as I see it nowhere in the literature today. I would be happy for Wikipedia to be the first place for it to be widely available. If you would like to pursue this, please contact me at jwf@ipac.caltech.edu or whatever way you prefer.

Regards,

John W. Fowler

Spitzer Science Center 134.4.23.49 18:33, 9 September 2006 (UTC)[reply]

California Institute of Technology

Can you send me a reprint, preferably in PDF format? PAR 15:19, 11 September 2006 (UTC)[reply]

The Maryland Astronomical Journal was a home-brewed journal in the Astronomy Program at the University of Maryland circa 1970. It was hand-typed by the chairman's wife, typos scrawled over by hand, and copies were produced on the new-fangled Xerox machine (we had just gotten over mimeograph). My paper, "Ionization Equilibrium in Stellar Plasmas", was 15 pages long, of which the first six are relevant here. I can scan those and convert them to PDF, but I'm not sure where to email the result. Please let me know how to do that and whether you prefer the entire paper. I gather there is some reluctance to use regular email, perhaps a Wikipedia policy? If not, a message to my email address above would allow me to send the PDF by return email.

Regards,

John W. Fowler

Reduced mass?[edit]

In Oxenius' Kinetic Theory of Particles and Photons (ISBN 0-387-15809-X), Appendix E.2, it is stated that the reduced mass of the electron (with respect to the electron-ion pair that may combine) should be used in evaluating the thermal de Broglie wavelength of the electron in the Saha equation. Is that wrong or applicable but just for some special case, or should this be changed in the article? --Tardis 23:28, 10 January 2007 (UTC)[reply]

"Detailed Derivation from University of Utah Physics Department"[edit]

This just appears to be a pdf of Wolfram Scienceworld. Is there something I'm missing here? --128.153.144.204 (talk) 01:57, 8 March 2010 (UTC)[reply]

The correspondent page at ScienceWorld (http://scienceworld.wolfram.com/physics/SahaEquation.html) is empty. 88.195.248.169 (talk) 20:25, 5 September 2015 (UTC)[reply]