Talk:Raman spectroscopy

Virtual energy state

Can somebody explain what a "virtual energy state" is? How is this distinct from a "true" energy transition (presumably one where the electrons are moved to an excited state)?

Since any wavelength radiation can theoretically cause the Raman effect, it then follows that the excited state most of the time does not correspond to any electronic/vibrational/rotational energy level. That is why the term "virtual energy state" is used. Mill haru 01:54, 8 January 2007 (UTC)

Can you provide a more thorough explanation or direct a link its explanation? I'm having trouble visualizing this virtual effect. Thanks. LostLucidity (talk) 19:44, 27 January 2008 (UTC)

In general the incident photon has far more energy than the difference between the ground state and the excited state. (In something like infrared spectroscopy, the incident photon has an energy equal to this difference and can be absorbed when the transition occurs). Thus the photon cannot be completely absorbed by causing the excitation. In essence therefore what happens is that the incident photon loses some of its energy and comes out at a lower frequency. However, in quantum mechanics we talk about transitions absorbing or emitting a photon with energy equal to the energy difference of the transition. To apply this language here, the ground-state electron must absorb the incident photon and move to a ridiculously high energy state, and then immediately emit a slightly less energetic photon, and move down to an excited state. It seems doubtful that this actually happens, and so they call it a virtual energy state, presumably because it sounds more impressive than `ridiculously high energy state'. It's a didactic model more than anything. 131.111.74.86 (talk) 16:29, 5 June 2008 (UTC)

Do you mean that the essence of the Raman effect still not clearly when using "virtual energy state" model to explain. I still wonder about the nature of the phenomenon. Could you explain it with out "virtual energy state"?. In flourescence, UV photons are absorbed and the molecule has a "ridiculously high energy state". So I think that a high energy state is very common. —Preceding unsigned comment added by 118.71.67.38 (talk) 06:10, 21 October 2008 (UTC)

Okay, so here's an analogy: You throw a tennis ball at a wall with a strange spring device in it (the details aren't important, but imagine the spring can be either compressed or relaxed, and it's got a way of being held in compression which can be toggled by the tennis ball). The tennis ball bounces back. If it comes back faster than it went in, then you know the spring was compressed, and got released by the tennis ball. By looking at the change in the ball's speed you can tell how much energy was in the spring. If it comes back slower than it went in, then you know the spring was relaxed and became compressed by the tennis ball. That's all that's going on, except that the photon's energy is given by its frequency rather than its speed. Also it's probably not the same tennis ball, but an identical one because of quantum mechanical stuff. So in the analogy, the spring needs to absorb a tennis ball with a very particular speed to become compressed - a speed much less than the speed of the tennis ball. But somehow it manages to absorb the tennis ball anyway, and it copes with all the extra speed by immediately releasing another tennis ball going slightly slower than the one that came in.Grj23 (talk) 11:21, 4 December 2008 (UTC)

Can someone provide more information on the following statement: "the lateral and depth resolutions were 250 nm and 1.7 µm, respectively, using a confocal Raman microspectrometer with the 632.8 nm line from a He-Ne laser with a pinhole of 100 µm diameter." The microscopic magnification would be an important piece of information if these resolution numbers are to be reproduced. Mill haru 02:24, 8 January 2007 (UTC)

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What does it mean that "The fingerprint region of organic molecules is in the range 500-2000 /cm"? If wavelengths are in units of length then why is the "fingerprint" given in inverse length?

Spectroscopists a weird bunch and as such decide to use wierd units, in this case the Wavenumber. They also tend to use the terms energy, wavelength, wavenumber and frequency interchangebly, since they all are related to energy. In Raman spectroscopy what is measured is the difference in energy between the scattered light and the excitation source, and the amount of energy involved is characteristic of a particular bond. For example, silicon has a primary band (or peak) at a Raman shift of about 520 /cm, and that is irrespective of the wavelength of the laser. A skilled spectroscopist will be able to tell simply from looking at a spectrum the major components of a sample as certain bands and features tend to correspond to specific Functional_groups --Wound 22:50, 4 Apr 2005 (UTC)

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This article could use some reorganizing: history should come before applications and applications should be merged with Raman microspectroscopy, other types, and see also. Additionally, at least in the RR article, there is a significant amount of repeated information, which may be more appropriately placed the main Raman article. Finally, the theory section should be expanded or an advance theory section should be added to do this topic justice.--Bjsamelsonjones

I think an experimental set-up section would also be a good idea. Including monochromatic incident light, reflection of the sample, filter to remove the rayleigh scattered light of the same frequency as the incoming light (which constitutes the bulk of the reflected light) a disperser (I think), and a detector. What disperser is used nowadays? Do practitioners use a michelson interferometer and fourier transform like in infrared spectroscopy? 131.111.74.86 (talk) 16:36, 5 June 2008 (UTC)

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This is a strange sentence: "Consequently in vivo time- and space-resolved Raman spectroscopy is suitable to measure cells, proteins, organs, and erythrocytes." First of all, what is meant by "measuring" cells or organs? Measuring the quantity or characterizing their chemical composition? Secondly, erythrocytes are a type of cell, so to say that Raman spectroscopy is suitable for measuring cells AND erythrocytes is redundant. —Preceding unsigned comment added by 69.181.124.113 (talk • contribs)

I reworded it to fix these problems. the wub "?!" 10:40, 4 July 2007 (UTC)

Comment about lateral and depth resolution

Hi every one, I would say that I am not completely agree with the example proposed to describe the lateral and depth resolution for a Raman microspectrometer.
First, about the lateral resolution of 250 nm. I think that a lateral resolution of 250 nm could be reached but not with a confocal microscope only. For your example, with a conventional Raman microspectrometer equipped with a He-Ne (632,81 nm) and a dry microscope objective of x100 (Numerical aperture = 0.9), the best lateral resolution you could have is around 1 micrometer. I think a resolution of 250 nm can be reached on AFM instrument coupled with a Raman spectrometer.
Secondly, the depth resolution depend on the nature on the sample. On a Si Wafer, the depth resolution is closed to 1 µm. On bone, the depth resolution decrease to 5 µm. It depends on the homogeneity of the sample. Generally, in spectroscopist review, everybody agree that the depth resolution is close to 1 µm.
If you want, I have reference concerning the use of Polarized Raman experiments in order to determine apatite crystals orientation in human teeth. Capsulcorp (talk) 15:16, 27 June 2008 (UTC)

Hi, I have to add something too. Is the graphic showing the raman energy levels correct that way? Atkins (Physical Chemistry) shows ∆J=±2. And the graphic in that book shows a difference in J before and after (anti-)stokes of (-)2. —Preceding unsigned comment added by 91.60.65.108 (talk) 02:41, 9 December 2008 (UTC)

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Suggestions

A citation for use of Raman spectroscopy with a wide range of excitation wavelengths is currently Reference [14], but this citation seems to be actually about biomedical imaging. This citation numbering issue should be investigated/resolved. — Preceding unsigned comment added by Slepkov (talk • contribs) 16:43, 14 October 2011 (UTC)

The doi of the Lombardi paper is wrong, it should be 10.1021/jp800167v. I don't know how to fix this and I don't have the time to read the manual.

It would be nice if the article included more info on isotope analysis with Raman microspectroscopy. This is a technique that is used in ecology and probably elsewhere. --151.205.213.57 (talk) 04:22, 9 May 2009 (UTC)

I'm wondering if Brillouin scattering should be included with Rayleigh in the context of scattering close to the exciter line.Periksson28 (talk) 19:46, 18 July 2009 (UTC)

Image - Raman Energy Levels

Isn't there a slight mistake in that image? As far I know the selection rule for IR-spectroscopy is v = ± 1 (not 2)!