Talk:Infrared spectroscopy

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The 'Typical Method' section of this article needs an edit to bring it out of the 1970s. The sort of non-FT method that's described isn't used by anyone anymore, and that type of machine hasn't even been available commercially for many years. You would be hard-pressed to find such a machine anywhere, except perhaps in the back of a university chemistry department's storage closet. In my opinion it should be eliminated entirely, or at least moved to the bottom of the article and placed in some sort of 'history of the technique' section. -July 1, 2005

It's probably useful for helping to explain what happens? Perhaps we could add a paragraph which says something like, "In practice, modern techniques use [fourier transform] techniques in order to determine the absorption spectra more precisely. At much lower frequencies detectors exist that can give the electric field over time, which may be transformed directly into a frequency spectrum. However at infrared frequencies (>600GHz) detectors cannot react fast enough, and so an [interferometer] (similar in principle to the one used in the [Michelson-Morley] experiment) must be used - this allows the signal to be recorded in the length domain. This signal may then be converted into the usual frequency spectrum." A source I had to hand for this is Modern Spectroscopy, 2nd Ed, J. Michael Hollas, ISBN: 0-471-93076-8 Grj23 (talk) 13:06, 5 June 2008 (UTC)

I guess rather than precision, the advantages of the FT method is that it detects a broad band of radiation all the time (the multiplex or Fellgett advantage) and that a greater proportion of the source radiation passes through the instrument because of the circular aperture rather than the narrow slit used for prisms or diffraction gratings (known as the Jacquinot advantage) (with the same source as my post above) (talk) 14:45, 5 June 2008 (UTC)

It might be helpful to add the equation for IR absorption frequency.

-- I agree. I'm brand new here, how does one add equations? I could write then up in MathType or MathCAD.


To add an equation just use the math tag or click on the \sqrt n button when editing. I'd put that equation in myself but I've but limited myself to editing only after at least 8 hours sleep the night before! Afn 09:27, 2 September 2005 (UTC)

IR-activity for symmetric CH2 stretch vibration[edit]

To my knowledge, the CH2 symmetric stretch vibration is IR-active. The reason is, that the dipole moment changes while the chemical group is oscillating. See e.g. [1] Therefore, the gif-animation, which states also that the methylene vibration is IR-inactive, should be changed.

The designations were added by an anonymous person five months ago. [1]. I think they should all be deleted: I know for sure that many are wrong right now, but there are a couple where I'm unsure what's correct (and I can't find a reference). The sentence before the animation implies that each mode is either IR-active or Raman-active but not both. This sentence should be deleted too. It is false for non-centrosymmetric situations like this. --Steve (talk) 12:01, 5 October 2012 (UTC)
I agree that those activity assignments cannot be generalized, see site for a counter example to some of the previous labels. I've removed the activity assignments and hopefully clarified the discussion about the number of modes. ronningt (talk) 15:56, 6 October 2012 (UTC)

value for carboxylic acid[edit]

The article puts the values for carboxylic acids as: carboxylic acids/derivates saturated carboxylic acids 1710 cm-1 unsat./aromatic carb. acids 1680-1690 cm-1 esters and lactones 1735 cm-1 (influence of conjugation and ring size like with ketones) anhydrides 1760 and 1820 cm-1 (both!) halogenides 1801 cm-1 amides 1650 cm-1 (associated amides) carboxylates (salts) 1550-1610 cm-1 (goes for aminoacid zwitterions as well)

but this site ( puts it as 2800-300 cm-1

so which is it?

Thank you.

The first values you've quoted were for the C=O adsorption in carboxylic acids. The ones you refer to from the other site seem to be for the O-H adsorption region, although that would be more around 3000-3500cm-1. A carboxylic acid has both groups, but the article has categorised their adsorptions separately, corresponding to the individual bonds, for simplicity. krebbe 15:09, 18 January 2006 (UTC)

IR spextroscopy on inorganic molecules[edit]

Since the article said that IR spectroscopy is also helpful or used in inorganic compounds, it is OK to include the fundamental vibrations of such inorganic compounds in the correlation table and the visual representation as well. --Aeron Valderrama 00:37, 11 July 2006 (UTC)

Sample Prep[edit]

Took out: "These salts do not absorb infrared light, so spectral lines will only appear from the analyte." Mediums such as KBr are used because they do not absorb IR light in the region most organic chemists are concerned with, but they do absorb IR light.

This section also needs a make over so it at least sounds like someone with a degree wrote it. Use of low/no prep diamond tip devices.

IR Correlation Table[edit]

The IR correlation table ought to be moved back into this article. The greatest reason is that one cannot find the article unless you look in the history of this article. Searching for "Infrared Specroscopy Correlation table" (the name of the article) doesn't find it at all. And in every book (that I've seen, and I've seen a few) covering IR spectroscopy for those intent on using it, a detailed table can be found.

I just think not including the correlation chart is like talking about a country without including a political map of its borders, it leaves out something of importance.


I don't want to be nitpicky, but isn't it "antisymmetrical" instead of "asymmetrical" stretching?

Lothar —The preceding unsigned comment was added by (talk) 17:39, 2 February 2007 (UTC).

It's usually asymmetric but 'antisymmetric can also be used. --Kkmurray 16:07, 5 April 2007 (UTC)


If this article is to be read by non-spectroscopists (and what is the point otherwise?) would it not be better to give the wavelength of the radiation used, instead of just its wave number? (maybe like this: ...(approx. wavenumber 400-10 cm-1, wavelength 25µm to 1mm) lying adjacent to the microwave region, has low energy and may be used for rotational spectroscopy. The mid- infrared (approx. wavenumber 4000-400 cm-1, wavelength 2.5µm to 25µm) may be used to study the fundamental vibrations and associated rotational-vibrational structure, whilst the higher energy near-IR (wavenumber 14000-4000 cm-1, wavelength 700nm to 25µm))... Moletrouser 06:35, 1 June 2007 (UTC)

example calculations[edit]

I think adding an external link to would be beneficial for this page. It's a site where one can simulate molecular spectra for any common molecular species, and view or download complete databases of molecular absorption line parameters. Access is free (subscriptions are needed for some advanced things). Visualizing infrared spectra in this way is very instructive, and I think appropriate here. What do you think? --Martin McHugh 17:02, 25 September 2007 (UTC)

Stop hand nuvola.svg
This is the last warning you will receive for your disruptive edits.
The next time you insert a spam link, as you did to Infrared spectroscopy, you will be blocked from editing Wikipedia. Persistent spammers may have their websites blacklisted as well, preventing anyone from linking to them from all of Wikipedia. Seriously, stop linking to your website. Its a conflict of interest and SPAM. Chuck Sirloin 18:38, 22 October 2007 (UTC)

Can we discuss this? I honestly don't think this is spam. The site is all about infrared spectroscopy and remote sensing. It's substantive and pertinent to the topic, and adds a great deal of depth and value I think. The fact that I've been associated with the site seems to be the problem, but that seems rather simplistic as a criterion. In discussion with the Wikipedia Administrators, it was requested that I post any external links to the talk pages first. I did this, and came back one month later to find that nobody voiced any objections. Exactly what guideline does this violate? --mm 19:03, 22 October 2007 (UTC)

I concur that Martyjmch tried to do the right thing here. If now editors don't think the link belongs, it's certainly discussable, same as any other content, but there were no objections when explicitly asked, so spam (or other) user-conduct warnings about adding it seem inappropriate. DMacks 19:35, 22 October 2007 (UTC)
I gave the warning because this user has been caution before by other editors about adding the link. Under conditions of COI, it was my understanding that the appropriate method was to post the link on the talk page, and if other editors thought the link was appropriate, they would add it, not the person with the COI. As I responded on User_talk:Martyjmch, my problem is with the link being a subscription site. That being said, if a consensus is reached by other editors that the link is needed, then so be it. --Chuck Sirloin 20:41, 22 October 2007 (UTC)
I'd lean against inclusion as it doesn't look like a unique external resource and doesn't seem to add much to the article here. There are multiple databases and calculators with various subscription models on the web (NB: this one does appear to have a free mode, I don't think "sign up for free account to use" is too commercial-like by itself, but there does need to be substantial quallity & quantity of free stuff), and Wikipedia is not DMOZ. What specifically is the unique content here? DMacks 20:54, 22 October 2007 (UTC)

Well, there are two unique things here, I think: 1) interactive online calculation and visualization of infrared gas-phase spectra, and 2) the display and access to the line parameters (e.g. HITRAN). Both seem appropriate to an article on infrared spectroscopy. To my knowledge, this is the only place you can do the former, and the easiest place to do the latter. Chuck Sirloin is correct -- I have a conflict of interest here (I am affilliated with the company that owns the site, and helped design the radiative transfer algorithms), so I will leave it to other editors if they would like to include it.--mm 15:40, 23 October 2007 (UTC)

Fingerprint Region[edit]

It appears that this page contains nothing about the so-called "fingerprint region" (~1500-1000 cm^-1). The part where it talks about "4000-400 cm-1 ... may be used to study ... rotational-vibrational structure" vaguely hints at it. I would be inclined to find some decent sources and add this information possibly next week, but can someone confirm that this topic is not discussed on some other page? Also, I think I could add a quantity of information roughly equal to the "theory" section in page length. I have never made an article before, so is it best to make something like this a separate article or added to this one?Dwr12 (talk) 02:56, 17 March 2008 (UTC)

I would think it should be added into this article, since it is an important part of IR spectroscopy. And something about the difference between stretching wavelengths and bending ones. If I can find my Spec book I will help... but I'm afraid I'm a newbie to editing so I'm not sure how much "help" I'd be. Should there also be something about the distinctive ortho, meta, para wavelengths? Hwinnian (talk) 05:00, 25 March 2008 (UTC)


In the subsection "Two-dimensional infrared spectroscopy", there are two "Main article" links, both of which are redlinked. Best I can tell, they've never gone to an actual subpage. Could someone look into where these are supposed to go? If there isn't an existing page, I think we can probably remove the {{Main}} links, at least until a substantial article is written. -- (talk) 20:03, 18 March 2008 (UTC)

Quantum vibration[edit]

Quantum vibration links here, but the introduction does not give any hint of why. Someone needs to add some detail in this area. 161 —Preceding unsigned comment added by (talk) 07:49, 2 April 2011 (UTC)

Certainly, it's a problem that "quantum vibration" redirects to this article which does not even mention the word "quantum" anywhere! I suggest changing it to link to Molecular vibration#Quantum mechanics. That's not perfect, but it's an improvement IMO. Any other ideas? :-) --Steve (talk) 09:22, 2 April 2011 (UTC)
Good question. Aside from the Molecular vibration article, I would suggest the Harmonic oscillator (quantum) article. The latter is more general and goes into greater depth on the quantum mechanics. I ran a Google search, though, and a recent spurt of news stories was definitely using quantum vibration to refer to molecular vibrations, so either link may be appropriate. ronningt (talk) 12:30, 2 April 2011 (UTC)


How about a section or at least some mention of how the polarity of a substance affects its wavenumber?

Jojojlj (talk) 03:10, 25 April 2011 (UTC)

Observations and Edit[edit]

There was mention of monochromator (interferometer) in picture but not in general article, that caused me pause to edit. Since the article appears to be about instrumentation then it needs to include explanations and issues (or references to issues) with instrumental analysis. My experience starts pre 60's to some post 90's, and not just Organic Chemistry, which focus makes this a substandard article.

Although Infrared spectroscopy has traditionally been used for Qualitative Analysis of Organic Chemistry products, it CAN be used for Quantitative analysis as well. Standard Additions method can be applied to most analytical methods and works well with Infrared as well. Infrared Spectroscopy has been used for analysis of Portland Cement ("Concrete"), minerals with H-O bonding, Gemstones, Carbon Nanotubes, and other industrial materials. Ceramics, q.v. Rare Earth containing Ceramics can re-emit (Fluoresce) Infrared at lower frequencies. This an issue in article Spectroscopy. Perhaps it is article quality, but the top level Spectroscopy does not reference Infrared Spectroscopy.

IR source linearity and stability is crucial. For far infrared, the low intensity of Blackbody can be augmented by using Silicon Carbide or other conducting ceramic that skews emission to lower frequencies. For analytical purposes, e.g. moisture detection (O-H stretching)), Light Emitting Diodes have been used as a source. Heating effects in sample and detector necessitate a narrow bandwidth monochromator after the emitter. Often windows of Germanium or other IR transparent material are used to exclude ambient radiation.

An Infrared detector is used and must respond evenly in the range to be measured. Far Infrared detectors typically respond slowly; they may need to be cooled because they respond to Room Temperature Infra Red also. Although newer instruments use semiconductor detectors, Thermocouples have been used and are still in use to detect infra red.

Shjacks45 (talk) 06:45, 11 July 2011 (UTC)

  1. ^ Colthup, Norman B. (1990). Introduction to Infrared and Raman Spectroscopy, Third Edition. Academic Press. ISBN 978-0121825546.