What is Ir spectroscopy: Definition and 17 Discussions

Infrared spectroscopy (IR spectroscopy or vibrational spectroscopy) is the measurement of the interaction of infrared radiation with matter by absorption, emission, or reflection. It is used to study and identify chemical substances or functional groups in solid, liquid, or gaseous forms. The method or technique of infrared spectroscopy is conducted with an instrument called an infrared spectrometer (or spectrophotometer) which produces an infrared spectrum. An IR spectrum can be visualized in a graph of infrared light absorbance (or transmittance) on the vertical axis vs. frequency or wavelength on the horizontal axis. Typical units of frequency used in IR spectra are reciprocal centimeters (sometimes called wave numbers), with the symbol cm−1. Units of IR wavelength are commonly given in micrometers (formerly called "microns"), symbol μm, which are related to wave numbers in a reciprocal way. A common laboratory instrument that uses this technique is a Fourier transform infrared (FTIR) spectrometer. Two-dimensional IR is also possible as discussed below.
The infrared portion of the electromagnetic spectrum is usually divided into three regions; the near-, mid- and far- infrared, named for their relation to the visible spectrum. The higher-energy near-IR, approximately 14,000–4,000 cm−1 (0.7–2.5 μm wavelength) can excite overtone or combination modes of molecular vibrations. The mid-infrared, approximately 4,000–400 cm−1 (2.5–25 μm) is generally used to study the fundamental vibrations and associated rotational–vibrational structure. The far-infrared, approximately 400–10 cm−1 (25–1,000 μm) has low energy and may be used for rotational spectroscopy and low frequency vibrations. The region from 2–130 cm−1, bordering the microwave region, is considered the terahertz region and may probe intermolecular vibrations. The names and classifications of these subregions are conventions, and are only loosely based on the relative molecular or electromagnetic properties.

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  1. Salmone

    I Doubts about Fourier transform of IR spectroscopy

    I was studying a Michelson interferometer for infrared absorption in Fourier transform and I've found these two images (taken from https://pages.mtu.edu/~scarn/teaching/GE4250/ftir_lecture_slides.pdf ) representing an infrared monochromatic beam of light going into the interferometer and the...
  2. R

    IR spectra (in thermal scope vs IR spectroscopy)

    In thermal imager vs IR spectroscopy, they both look at the IR radiation of an object. What is the difference between the two.. I know IR spectroscopy look at the dipole moments of molecules. But in thermal imager.. do they also image the dipole moments of molecules? Also why you see images in...
  3. JeremyC

    IR and Raman spectroscopy question

    Homework Statement Sulfur hexafluoride is a centrosymmetric molecule with four infrared inactive vibrational modes: 346 cm-1 , 524 cm-1 , 643 cm-1 and 775 cm-1 The Raman spectrum of a liquid sample of SF6 (held at elevated pressures) was measured with a laser that has a centre frequency of...
  4. Amy B

    Ordering Carbonyl Group Wavenumbers in NMR

    Homework Statement I want to put these in order of increasing wavenumber for the absorptions of the carbonyl group in an nmr spectrum Homework EquationsThe Attempt at a Solution I know that the third one is the highest, the NH ketoamine is the lowest and last one is the second lowest but I'm...
  5. B

    Infrared spectroscopy to find water absorption lines

    Hi I am currently trying to find the water absorption lines by using a Michelson interferometer, as a detector I am using an ocean spectrometer. The data obtained is thus the spectrum's "received" by the spectrometer. Am I right to assume that in order to find the absorption peak/peaks I should...
  6. B

    What gases can be absorbed between 800 and 1000nm wavelength?

    Hi I was wondering if anyone could tell me what gasses are absorbed between 800 and 1000nm wavelength and weather there is a book that lists all the gas wavelengths that can be absorbed in this region Thanks bertopolis
  7. B

    What do the symbols \delta and \upsilon represent in IR spectroscopy?

    Hi there. First time PF poster. I have a question about interpreting IR spectro graphs. I get the general idea of interpreting the sharpness and strength of the line but when I need to ID the pulse down I have to choose between \delta and \upsilon (or mabe its just v) version of the...
  8. M

    Zero point energy and IR spectroscopy

    I made some frequency calculations in Gaussian (using various method/basis set combos) and I have to find which method/basis set combo is the most accurate by comparing the results to literature values. I got the calculated wavenumbers along with their intensities but my professor tells me I...
  9. J

    (long) question - Raman, IR spectroscopy; virtual energy states, light; heat

    I'm confused about what is going on theoretically with Raman, and light in general, wrt photon absorption, annihilation, and re-emission; I don't have the math background to understand Fourier transform, of anything past simple algebra anymore, but would like to at least have a decent...
  10. S

    IR Spectroscopy: Examining Absorption of Water, CO2 & Methane

    I've been doing IR spectroscopy to examine to the absorption spectrum of water and carbon dioxide, after which I took another absorption spectrum with a methane gas cell. The absorption spectrum without the methane shows absorption from carbon dioxide around 4000nm, however, this is not apparent...
  11. J

    Detecting hydrogen gas via IR spectroscopy

    Say I want to monitor the interface of an electrochemical cell via IR spectroscopy. If H2 gas is generated, there must be a characteristic IR signature to this event. How can I figure out what this is? Are there calculations for this? I'm sure this is in the literature somewhere, but I...
  12. M

    Basic IR Spectroscopy and dipole moments

    Hi Why does a bond stretch or vibration have to cause a change in dipole moment to be IR active? Presumably all vibrational modes depend on energy aborption to occur whether they cause a change in dipole or not. I'm presuming that only those vibrational modes that cause a dipole change are...
  13. W

    What are the different types of motion in a CH2 group in IR spectroscopy?

    Quoting from wikipedia I understand what symmetrical and antisymmetrical stretching come from and the number of vibrational mode(s) can be predicted basing on the concept of degree of freedom. However, for scissoring, rocking, wagging and twisting, are they considered as bending...
  14. M

    IR Spectroscopy Help for Organic Chemistry

    I am taking my second semester of organic this summer. We are working on IR Spectroscopy and mass spectrometry in class. Is there anywhere that anyone knows about that may put it all together? Or can anyone maybe give me some tips on how to remember all of the main functional groups? I am...
  15. A

    IR Spectroscopy - HATR: Thickness & Experimental Design

    i need help in determining thickness of thin film created by pouring volatime solvent with solute using HATR technique also would like to know how experimental design can be set with HATR technique quantification purpose.
  16. S

    NMR and IR Spectroscopy of Unknown

    Homework Statement I have attached the IR and NMR spectrum from lab. I have determined that there was a nitrogen present in the compound. There was no sulfur or halogens. The molecular weight was 138. The compound was solid and yellow color. It had a melting point between 124 and 134 C...
  17. P

    Raman and IR spectroscopy

    Homework Statement For (NO)2+, experiments show 1 Raman active vibrational mode around 1450/cm; 2 strong IR active modes at 2400/cm and 550/cm; and 1 weak IR active mode around 3600/cm. What does that say about its geometry? The Attempt at a Solution Never mind, I think I got it :)