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Questions tagged [ir-spectroscopy]

Use this tag for questions regarding the principles and application of infrared spectroscopy.

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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 ...
Mäßige's user avatar
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2 votes
1 answer
183 views

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 ...
jackisquizzical's user avatar
3 votes
0 answers
53 views

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-...
Mäßige's user avatar
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8 votes
2 answers
646 views

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 ...
Jonathan's user avatar
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0 answers
26 views

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 ...
Microbiologie13's user avatar
1 vote
0 answers
17 views

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 ...
jasw's user avatar
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4 votes
0 answers
117 views

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-...
Benvz's user avatar
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5 votes
1 answer
900 views

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 ...
dispatchh's user avatar
3 votes
0 answers
28 views

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 ...
Aether's user avatar
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33 views

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 ...
Benvz's user avatar
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2 votes
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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 ...
MrArsGravis's user avatar
1 vote
1 answer
49 views

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 ...
Benvz's user avatar
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-2 votes
1 answer
39 views

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, ...
user3713179's user avatar
2 votes
0 answers
115 views

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 ...
Tkh97's user avatar
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9 votes
2 answers
383 views

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 ...
isolated matrix's user avatar
2 votes
2 answers
185 views

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 ...
Ankit's user avatar
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5 votes
2 answers
100 views

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 ...
soravoid's user avatar
-2 votes
1 answer
353 views

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 ...
Daniel's user avatar
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3 votes
1 answer
249 views

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 ...
Audrix's user avatar
  • 137
6 votes
1 answer
228 views

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 ...
Ahmad's user avatar
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2 votes
1 answer
181 views

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 ...
Zyxl's user avatar
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0 votes
0 answers
42 views

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?
RumanACl's user avatar
4 votes
2 answers
227 views

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 ...
Simon Joubert's user avatar
-1 votes
1 answer
61 views

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?
user127280's user avatar
1 vote
0 answers
70 views

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 ...
Justanotherchemist's user avatar
7 votes
1 answer
326 views

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....
uhoh's user avatar
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3 votes
0 answers
322 views

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 ...
Jamo's user avatar
  • 31
3 votes
1 answer
141 views

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 ...
ScepticalChymist's user avatar
1 vote
1 answer
2k views

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-...
warren's user avatar
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2 votes
1 answer
108 views

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 ...
VinalV's user avatar
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3 votes
1 answer
523 views

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 ...
Andreas's user avatar
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4 votes
0 answers
106 views

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 ...
user4723's user avatar
  • 305
0 votes
1 answer
155 views

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. ...
lazearoundallday's user avatar
9 votes
2 answers
1k views

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 $\ce{Fe2(CO)9}$. ...
kocall4's user avatar
  • 91
3 votes
1 answer
60 views

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 ...
mcocdawc's user avatar
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0 votes
1 answer
777 views

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?
Asm Saikat's user avatar
0 votes
1 answer
913 views

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 $cm.molecule$). ...
mranvick's user avatar
  • 536
1 vote
1 answer
159 views

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) ...
Anton's user avatar
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7 votes
1 answer
585 views

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 ...
AChem's user avatar
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8 votes
1 answer
1k views

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.). ...
S R Maiti's user avatar
  • 5,685
2 votes
0 answers
102 views

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 ...
DJA's user avatar
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1 vote
0 answers
112 views

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, ...
user avatar
3 votes
1 answer
1k views

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 ...
user avatar
3 votes
2 answers
850 views

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....
user avatar
3 votes
1 answer
1k views

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 ...
R M's user avatar
  • 31
2 votes
0 answers
45 views

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 ...
Tim's user avatar
  • 21
0 votes
2 answers
129 views

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 ...
John Ladasky's user avatar
1 vote
0 answers
41 views

Comparing bond strength by IR frequency: symmetrical modes

In literature the stretching mode of $\ce{CO}$ is often said to be the diagnostic criteria for strength of back-donation by virtue of weakening the $\ce{CO}$ bond. However, when speaking about ...
permeakra's user avatar
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-5 votes
1 answer
594 views

Why does the infrared spectrum of HCl only have one peak? [closed]

Suggest one reason why HCl has only one peak? Does this have something to do with fact that peaks (in IR spectroscopy) represent areas of the spectrum where specific bond vibrations occur and ...
VENDINGMACHINE's user avatar
3 votes
1 answer
3k views

Identifying the molecular structure of compound with sum formula C8H14O3 formula using NMR and IR spectrometry data

I am looking to identify the molecular structure of a compound with the sum formula $\ce{C8H14O3}$ using the NMR and IR spectrometry data below. I was able to figure out the molecule as My friend ...
benzene11's user avatar
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