Questions tagged [ir-spectroscopy]
Use this tag for questions regarding the principles and application of infrared spectroscopy.
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In theory, is it possible to elucidate crystal structure using IR data with an accuracy comparable to XRD or are there fundamental limitations?
Obviously, IR is extremely hard to fully interpret for all but the simplest molecules, so that's more of a theoretical question, but... In principle, IR contains all the data about chemical structure ...
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Is any significant product formed in the gas phase when reactants' concentrations are in the hundreds of ppm?
Title says it all. I am evaluating the chance that the IR signal of a mixture of gases changes due to their reaction with each other. Keep in mind that they are in the 3-3000 ppm range and include a ...
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Why does the IR-spectrum of N-methyl diethanolamine have two peaks in the 1080-1020 cm-1 area?
I found two peaks in the IR-spectrum of N-methyl diethanolamine in the area of 1080-1020 cm-1, while the IR-spectrum of diethanolamine has only one peak in this area:
(Blue is N-methyl diethanolamine,...
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Why is the R-branch in rovibrational spectroscopy bigger than the P branch?
I was conducting a rovibrational IR experiment and noticed that for HCl, the P branch is always lower in intensity than the R branch.
I already understand that the intensity of the spectral lines is ...
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Ozone from 10um IR?
Ozone is easily produced by Hg lamps with <200nm power (peak@185nm), but O2 also strongly absorbs around 10um. I've poked around but can't find any discussion of ozone production at 10um. Is the ...
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Interpretation of IR spectrum
I was trying to identify the following IR spectrum as part of an exercise sheet of my spectroscopy course.
What I know from the spectrum, is that we have broad OH stretching vibrations at $\pu{3200-...
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FTIR Spectra: Did I synthesize ethyl gallate from gallic acid?
I successfully synthesized ethyl gallate from gallic acid and ethanol (of course there are other reagents too, like DCC and Pyridine). Before conducting FTIR analysis, I performed column ...
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FTIR data: Is there a way to obtain stat significant differences observed between groups in LD-PCA?
Besides checking the loadings and choosing peaks of interest, there is a way to point out from the LD-PCA or PCA the differences between groups that are significant?
All ideas are very much ...
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Is there any uv-vis sensor that installs on a pipe like other measurement tools like flowmeter or temperature sensor?
I am looking for an industrial UV-vis sensor that is installed on a pipe like other measurement instruments like temperature and flow transmitters.
I researched this subject and I found one model but ...
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Why does CO lack a Q-branch in its rovibrational spectrum as opposed to NO?
Since I assumed that if NO has a Q-branch, then so should CO. However, this explanation of rovibrational spectroscopy says otherwise: https://pages.vassar.edu/magnes/2018/12/15/fundamental-...
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Help interpreting IR Spectrum of Vanillin ("aldehyde bands")
I'm not sure about the attributions of 3 bands of my ATR FT-IR spectrum of an extract of vanilla sugar, that probably contains mainly vanillin and some impurities. The extraction solvent was ethyl ...
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Can multispectral imaging be used for identification of materials, substituting for hyperspectral imaging?
Nowadays a lot of research and applications are using Hyperspectral Imaging for identification and segregation of plastics by material. But the cost of a HSI system is quite high.
Could a ...
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How do I denote a specific rovibrational transition?
I am using a linelist from HITRAN, which gives me a whole lot of extra data and I want to denote the transitions accurately. But I don't know what to use for rovibrational transitions. The following ...
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How are Fermi resonances between normal modes possible?
As I understand, Fermi resonances occur when two (nearly) resonant vibrational states—most commonly a fundamental and overtone or combination mode—that are of the same symmetry interact, which, in the ...
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What is the relation between cross-section and spectral line intensity?
I was told by my supervisor that there is a relation between these two and he talked about a coefficient connecting the two of them. I am currently brushing up a lot of chemistry as I'm a physics ...
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What the book means for "percentage difference"?
From Atkins-De Paula, Physical Chemistry, Ninth Edition, page 485
Not sure what the books means as "percentage difference".
Btw, this is my attempt
Fundamental vibration, in wavenumber, ...
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Calculating Rotational Temperature from an FTIR Spectrum
I am trying to calculate the rotational temperature of a sample of gas phase HCN from an FTIR spectrum. It's a 10 Torr sample in a 10 cm gas cell, held at room temperature. In theory, I should be able ...
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Software to draw one-dimensional PES including vibrational energy levels
I am trying to represent the difference between the an anharmonic and harmonic treatment of vibrations. The easiest way to do this is to present an example of a harmonic and anharmonic potential ...
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Datasets of Light Absorbance Spectra for Atmospheric Gases
I am currently doing some thermal/aerospace engineering research that involves finding light absorption in different points in Earth's orbit.
What is the best way to find absorbance vs. wavelength ...
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How to get continuous spectral data into intensities of channels centered around wavelengths?
Currently, I am looking into using a spectral sensor from SparkFun in order to obtain spectroscopic data to feed into a trained neural network, however this sensor gives intensities based on inputs ...
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How to read 1H-NMR- and IR-spectre (for ibuprofen) [closed]
I have read the answers to related/similar questions. They didn't help.
I have to read a proton-NMR-spectrum and an IR-spectrum of ibuprofen. The structure formula is given to:
I have not been ...
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Why does H2O appear as spikes in IR of air?
In the IR of air shown below, the region for water at 1500 cm-1 is hard to individually assign peaks due to their "spikey" nature. Is there any specific reason for this or does it just ...
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Why does the FTIR-ATR spectrum for hexamethylenediammonium adipate not have a peak for the N-H bond?
I have synthesized pure hexamethylenediammonium adipate by reacting equimolar quantities of adipic acid and hexamethylenediamine in ethanol. The diammonium salt, being insoluble in ethanol, was ...
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How to interpret this pair of IR and 1H NMR spectra?
I need to figure out the structure of a $C_{8}H_{14}O_{2}$ molecule with this IR spectrum:
and these $^{1}$H NMR spectrum signals:
m means 4 or more spikes.
I worked out that the degree of ...
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Whats a good solvent to analyze amygdalin in FTIR?
What solvents would be good to analyze amygdalin using FTIR spectroscopy? Will carbon tetrachloride react with the amygdalin if used as a solvent?
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What can be reasons for such anomalies in the IR spectrum of iodoform?
A few weeks ago I collected an IR spectrum of iodoform in KBr as part of a computational chemistry course. For some reason, there is consistently a trough right before every peak, and I am unsure of ...
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Help with chemical bond associated with 1500cm-1 and 1600cm-1 [closed]
I have IR spectra of polystyrene with characteristic peaks at 1450cm-1. 1500cm-1 and 1600cm-1. What chemical bond is associated with 1600cm-1 and 1500cm-1?
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IR / Raman factor group analysis (site and factor group determination)
I'm currently trying to interpret some IR and Raman spectra of solid state compounds. They show a simple molecular unit of which the expected bands are split due to the coordination in the crystal ...
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How exactly thermal infrared (e.g. FLIR) cameras image methane leaks? Are they measuring a temperature difference or an emissivity difference or...?
The story Infrared camera shows the impact of vehicle emissions says:
In an effort to visually demonstrate the potentially fatal impacts of air pollution, FLIR Systems (Wilsonville, OR, USA; www.flir....
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What Is This Small Peak That Always Occurs Within Ketone Infra-Red Analysis?
After looking at a bunch of IR spectrums for ketones, I have noticed this tiny peak that I circled on the diagram below. Does anyone know what it actually is and if I can always use it to distinguish ...
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Why my Infrared data acquired in transmission mode looks like it was acquired in absorbance mode?
I'm analyzing some carbon nanotubes with DRIFTS. I mix the CNT with KBr powder and proceed to measure the spectrum of the powder. After acquiring the KBr background (in %T, peaks facing down) I ...
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Effect of electron-donating and electron-withdrawing groups on the C=O bond
My notes states this:
An electronegative element tends to draw in the electrons between the carbon and oxygen atoms through its electron-withdrawing effect. This strengthens the C=O bond.
An electron-...
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Why does the ν1+ν4 combination band for methane occur?
I am looking at the normal modes for methane and have attached a figure of them below:
The only IR active modes are $\nu_3$ and $\nu_4$ which I understand because the other two modes do not change ...
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Paracetamol infrared spectrum issues
I was studying Infrared Spectroscopy and i analyze different polymers. When i prepared paracetamol making a pill mixing 2mg of it with 200mg of $\ce{KBr}$ on a vacuum-connected press when i put it in ...
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A Multistep Reaction Provided with IR Spectra (Guessing Started with Esterification)
Below, IR spectra for this sequence are provided:
For compound E, I suggest the formation of a conjugated ester with the elimination of $\ce{-OH}$ group. The IR peak at $\pu{1732 cm-1}$ is a ...
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Why is this graph of vibration spectroscopy like this?
This graph shows the absorbance of different wavenumbers of infrared radiation causing different forms of vibrations of the water molecule. I would like to know why the graph turns out the way it is.
...
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Why are there two infrared vibrational frequencies for the terminal CO ligands of Fe2(CO)9?
I am struggling to rationalise why there are two infrared vibrational frequencies ($\pu{2082 cm^-1}$ and $\pu{2019 cm^-1}$) for the stretching of the terminal $\ce{CO}$ ligands of $\ce{Fe2(CO)9}$. ...
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Error in calculating G-matrix
I have a question regarding the calculation of the $G$-matrix in the classic
"Molecular vibrations" textbook by Wilson (1955, McGraw Hill).
On page 63 it gives an example for the calculation ...
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Why the count of the IR band of H2O and CO2 is different? [closed]
Why $\ce{H2O}$ shows three and $\ce{CO2}$ shows two fundamental bands in IR while they both are triatomic molecules?
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Conversion from Spectral Line Intensity to Absorbance (HITRAN)
The HITRAN spectral database gives access to the spectral absorption lines of various gaseous species. These lines are given as $S$ values in units of $cm^{-1}/(molecule·cm^{-2})$ (or $cm.molecule$).
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Vibrations of metal complexes (polyatomic molecules)
I am reading about vibrational spectroscopy of polyatomic molecules and specifically about metal complexes. What I don't understand is what happens on the vibrational modes of the ligand (e.g. water) ...
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How is the vibration of multiple atoms treated in vibrational spectroscopy?
Most of the advanced undergraduate textbooks on physical chemistry/ instrumental analysis show the case of a diatomic harmonic oscillator and derive formulae for predicting the frequencies. The ...
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How to interpret the relation between CO stretch frequencies and backbonding strength for polycarbonyl compounds?
I am working on a series of octahedral complexes of the type $\ce{[M(CO)2(CH3)X3]-}$ where $\ce{M} = \ce{Co}, \ce{Rh}, \ce{Ir},$ and $\ce{X}$ is a range of ligands (halide, cyanide, nitrosyl, etc.). ...
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Why is the intensity of the IR spectra of IBr higher than that of ICl?
Why is the intensity of the IR spectra of $\ce{IBr}$ higher than that of $\ce{ICl}$?
I know that the IR spectra intensities are proportional to the derivative of the dipole moment with internuclear ...
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Should Birge–Sponer plots always have a negative gradient?
I have a set of data I would like to use the Birge–Sponer extrapolation with, but the data is the wavenumbers of the bands in the vibrational-electronic spectrum of a diatomic molecule for $v' = 0, 1, ...
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Comparing the zero point vibrational energies of DCl and HCl
(a) Compare the zero point energy (i.e. $E_0)$ in joules for $\ce{H^{35}Cl}$ and $\ce{D^{35}Cl}$ (assuming both are anharmonic oscillators).
(b) Explain the effect this will this have on their ...
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How does the force constant change when a heavier atom is used in vibrational spectroscopy?
(iii) The fundamental band in the IR spectrum of $\ce{^1H^{127}I}$ is found at $\pu{2308 cm^-1}.$ Calculate the force constant for the bond. Assume the molecule can be treated as a harmonic oscillator....
user85551
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Why is the ester carbonyl peak in benzocaine IR spectrum so low?
Having looked at multiple IR spectra for benzocaine, I am struggling to understand why the carbonyl C=O peak is so low in the spectra compared to where an ester carbonyl group usually is on other IR ...
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Why are Methyl vibr. modes called r modes and methylene vibr. modes called d modes
I am coming from a chemical background and currently work in the field of vibrational spectroscopy. When I talk to fellow physicists or chemists I always encounter the same question. "Why are the ...
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Seeking safe, water-soluble chemicals for an IR spectroscopy experiment
I am working with a custom-built device which is intended to perform some mid-infrared chemical measurements. It consists of four thermopile sensors with optical windows. In front of each window is ...
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