Talk:Electron spin resonance

Needs for the article

• Relaxation times
• Saturation effects
• Effect of multiple unpaired electrons on an atom/in a molecule - tukan 17:19, 13 Dec 2004 (UTC) and Dirk Beetstra ^{T C} 15:15, 21 July 2006 (UTC)
• Spin traps - Jasoninkid
• Instrumentation? - Astrochemist 15:37, 24 May 2007 (UTC)
• The applications section is weak for such a long article. - Astrochemist 15:37, 24 May 2007 (UTC)

Content and organization

I moved some of the introductory material to sections further down in the article. This allows the reader to see the contents box more easily. - Astrochemist 03:37, 10 May 2007 (UTC)

I removed the following:

"Beyond these considerations, as $\nu$ increases the n_MJ+1 grows exponentially, so high-field EPR spectra are saturated at lower P as compared with X-band measurements."

I deleted the above sentence as I could not readily see how raising a spectrometer's frequency would cause the upper energy state to be more populated. It seems that just the opposite would be true. Am I missing something? - Astrochemist 04:43, 22 May 2007 (UTC)

Do we need an animated gif in the final section? How about a simple picture showing several spectra, each at a different microwave frequency? - Astrochemist 02:24, 23 May 2007 (UTC)

I don't think so. In fact, a good deal of this article has been written by somebody with a particular interest in high field ESR, hence all the links to Russian stuff. I would suggest that the final section could be spun out to a new article on high field ESR, since the article is already getting on the long side. Good work on this article though - I've been meaning to do it for ages and never got round to it! Chris 08:08, 23 May 2007 (UTC)

PS: Do we really need to give g to all those decimal places? It's given on the g-factor page, though it has a different value there!.

I agree with what you wrote above. I changed the picture with the nitroxide spectra (now a bit fuzzy) and I see that you've altered g_e. -- Yesterday I traced the high-field EPR material to a Russian lab's web pages, and added the appropriate link. Since those pages have a copyright notice, I'm not sure how much of their material can be used in this particular Wikipedia article. -- Astrochemist 15:37, 24 May 2007 (UTC)

The g-value section

NMR spectroscopists usually interpret changes in line positions in terms of shielding constants ($\sigma$), but EPR spectroscopists usually interpret changes in line positions in terms of g-value variations caused by spin-orbit coupling. This Wikipedia article has both, so I'd like to remove the shielding constant material. (It can always be put back in if I'm wrong.) -- Astrochemist 19:21, 24 May 2007 (UTC)

Errors in the article

The magnetic moment of an electron is approximately the Bohr magneton, it is NOT the gyromagnetic ratio of the electron times the Bohr magneton (which would approximately be the Larmor frequency). Changes in the resonance frequency of an electron in a chemical environment do not arise from changes in either the spin angular momentum or the gyromagnetic ratio. The former is a fundamental property of any spin 1/2 particle, while the latter is a fundamental property of the electron. Rather, the coupling of the electron magnetic moment to nuclear magnetic dipoles, or the spin-orbit coupling alters the energy difference between the spin up and spin down states, leading to a frequency change the provides information about the chemical environment. In simpler terms, the local magnetic field an electron experiences depends on it environment, so different chemicals cause slighty different field strengths at the electron, and thus shifted resonance curves (and different linewidths!).

• The initial version of the above was added anonymously on 21:41, 6 April 2006 192.55.208.10. I believe that the points raised have been corrected. - Astrochemist 19:21, 24 May 2007 (UTC)

EPR questions

How is elecron spin resonance used to date material?

I read the following on the BBC news website, concerning the dating of the human footprints in the Americas (article Footprints of 'first Americans' by Paul Rincon - link http://news.bbc.co.uk/1/hi/sci/tech/4650307.stm).

The researchers used radiocarbon dating on shells and animal bones in the sequences and dated mammoth teeth by a technique called electron spin resonance. The sediments themselves were dated by optically stimulated luminescence.

Answer: Radiocarbon dating uses, that the composition of Isotopes depends from the age. Usually one uses a mass-spectrometer to measure the composition. I guess, that ESR is used, because its not invasive, so the Object will not be harmed/destroyed by the measurement. The annormal Zeeman-effect leads to different line-structures in ESR-measurement, if you have different Isotopes. From the Absorption-Intensities one can conclude the composition and indirectly the age? I know that this is theoretically possible, but I doubt whether it is an accurate method.

Can ESR be used as a technique for analysis of antioxidants???

Answer: Yes kinda, ESR can see free radicals, especially with the use of a spin trap, therefor ESR can see free radicals going away and thus the affect of the antioxidants. - Jasoninkid