Questions tagged [ir-spectroscopy]
Use this tag for questions regarding the principles and application of infrared spectroscopy.
158
questions
3
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1answer
31 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 ...
0
votes
1answer
66 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?
0
votes
1answer
52 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 $cm.molecule$).
...
1
vote
1answer
53 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) ...
6
votes
1answer
199 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 ...
7
votes
1answer
139 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.). ...
2
votes
0answers
34 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 ...
1
vote
0answers
37 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, ...
3
votes
1answer
234 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 ...
3
votes
2answers
78 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....
3
votes
1answer
142 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 ...
2
votes
0answers
32 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 ...
0
votes
2answers
64 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 ...
1
vote
0answers
28 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 ...
-5
votes
1answer
168 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 ...
3
votes
1answer
860 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 ...
3
votes
1answer
67 views
Lack of elaboration in IR spectra of compounds
I've recently started learning about IR spectroscopy, and a common trend I'm seeing in my textbook and other sources is that not all the features in the IR spectrum are explained in detail. The focus ...
1
vote
0answers
18 views
pH Dependency of IR Stretching Frequency in CO-binded Heme Protein
If one consumes CO, then CO binds with Heme Protein forming a Fe-CO bond. My question is if there will be any pH dependency on IR Stretching Frequency, i.e. ν(CO) and ν(Fe-CO). And if there is, then ...
0
votes
1answer
36 views
What functional groups can 900-2500nm IR spectrometers detect?
3700 cm-1 corresponds to about 2,700 nm
650 cm-1 corresponds to about 15,000 nm.
Many cheap IR spectrometers ($7000 or so like the ones at Stellarnet) has range of 900nm to 2400nm (or 11,111 cm-1 to ...
2
votes
0answers
42 views
Finding wavelength of the centre of Stokes Ro-vibrational spectrum
I have the following rovibrational Raman spectrum for $N_2$:
and I am trying to calculate the "wavelength where the centre of the Stokes ro-vibrational spectrum would be observed" if the $...
0
votes
1answer
56 views
IR absorption chart
I am taking a course in structural determination of organic compounds. Right now, we are giving the IR spectra.
I am looking for a table, as detailed as possible, of the absorptions. I hope you can ...
1
vote
0answers
26 views
How can I cluster infrared spectra?
This is sorta a cross-post from my post in StackOverflow. Although, rather than seeking help with the code I'm here asking for help with a chemical/statistical problem associated with the code.
I'm ...
-1
votes
2answers
170 views
How to determine the unknown molecule using the infrared spectroscopy?
An unknown sample was analysed using infrared spectroscopy. What is
the compound?
So I am having difficulty in using the infrared data to determine the unknown compound. I keep on misinterpreting the ...
0
votes
1answer
43 views
Does increasing the number of interferometers increase signal in FT-IR?
I'm trying to understand why most modern FT-IRs have three interferometers. Does this improve the signal in someway or does it have another effect?
1
vote
0answers
25 views
Using the method of differential absorption to determine the ethanol content of an unknown sample [closed]
I have completed a whole set of FITR-ATR spectra analysing 6 solutions of ethanol-water mixtures, all at different concentrations of each.
I have now been instructed to use the method of differential ...
-1
votes
1answer
129 views
Is acetylene IR active? [closed]
I've a very straight forward question, I'm confused because I've been told that a atom which has a oscillating transient/permanent dipole is IR active. But there are few asymmetric stretching/bending ...
7
votes
2answers
1k views
Why does ethylamine have two infra-red spectra? Are both correct?
The one I have in my textbook is this:
Shouldn't the first trough at $3500$ to around $3000$ mean that it's an $\ce{O—H}$ group with a $\ce{C—H}$? And then the other trough at $1700$ be a $\ce{C=O}$? ...
0
votes
0answers
62 views
Estimate the relative intensities of absorption given the split in energy levels
Estimate the relative intensities at $\pu{25 °C}$ of absorption originated in the ground state and the first excited state when the energy levels involved are separated by:
(a) $\pu{10000 cm^-1};$
(b) ...
-2
votes
1answer
51 views
Detecting carbon dioxide concentration using mosquito neurons
At the Mauna Loa Observatory the concentration of atmospheric carbon dioxide is measured using the absorption of infra-red light. This is a statistical technique that requires constant careful ...
2
votes
1answer
219 views
Comparison of two spectra in order to find whether the irradiated sample has significantly different resulting spectra
I would like to compare two absorption spectra ( or interferograms) and conclude whether between these two there are statistically significant differences at particular wavelength intervals. At the ...
1
vote
1answer
170 views
Methods used to compare two spectra in order to determine the effects of irradiation of sample
I would like to compare two absorption spectra (or interferograms) and conclude whether between these two there are statistically significant differences at particular wavelength intervals. At the ...
2
votes
1answer
389 views
XPS/EDS vs FTIR/Raman [closed]
So I have been studying the four methods the past couple of weeks. To my understanding, XPS is a very surface-sensitive technique. It can give information about the composition of the surface but also ...
1
vote
1answer
194 views
Can you measure an IR spectrum of a sample inside a glass vial?
If I have a sample of some compounds dissolved in water inside a glass vial (let's say quartz). Would it be possible to get a usable measurement through this glass vial without too much absorption by ...
0
votes
0answers
51 views
Raman or FTIR spectroscopy to identify metals?
Metals are opaque, so doesn't most of the light reflect? And does the IR source even cause vibrations in the metal?
Same goes for Raman spectroscopy, is it useful for use of metal identification?
Is ...
3
votes
1answer
87 views
PE expression for vibrational spectra of molecules using Newton's second law
I am currently studying the textbook Infrared and Raman Spectroscopy: Principles and Spectral Interpretation, second edition, by Peter J. Larkin. Section 10. Calculating the Vibrational Spectra of ...
1
vote
0answers
57 views
$Q_3$ is symmetric with respect to the $\sigma_v$ operation?
I am currently studying the textbook Infrared and Raman Spectroscopy: Principles and Spectral Interpretation, second edition, by Peter J. Larkin. Section 8. Symmetry: Infrared and Raman Active ...
3
votes
1answer
564 views
Identify the structure of compound with C₉H₁₀ formula using IR and NMR data [closed]
Use IR and NMR data to define the structure of the molecule, the formula of the given structure $\ce{C9H10}.$
On what basis do we conclude that its structure is that (the answer) only? On what points ...
2
votes
0answers
285 views
What is the precise meaning of "in-phase" (and "out-of-phase") in this context?
I am currently studying the textbook Infrared and Raman Spectroscopy, 2nd edition, by Peter Larkin. In a section entitled Symmetry: Infrared and Raman Active Vibrations, the author says the following:
...
3
votes
0answers
20 views
Any large databases of IR Spectra that you are able to download many spectra in bulk [closed]
I am currently working on a machine learning project, in which I need access to many IR spectra, the more the better, in order to build a classifier that will used some unsupervised learning in order ...
1
vote
1answer
47 views
Raman scattering and "electron and proton center" of molecule
I am currently studying the textbook Infrared and Raman Spectroscopy, 2nd edition, by Peter Larkin. In a section entitled The Raman Scattering Process, the author says the following:
Light scattering ...
0
votes
0answers
49 views
Explaining allene IR stretching frequency
So I was comparing the IR stretch frequency of ethyne, ethene and allene. Of course triple bond is stiffer than double bond so ethyne has a higher stretch frequency. The problem then is where allene ...
0
votes
0answers
2k views
The IR/ H-NMR analysis of benzophenone?
I think I have figured out the IR spectrum for benzophenone. Would it be that the sharp peak in the middle (1700 cm^-1) is for the ketone and the little peaks pass 2900 cm^-1 rang are the sp2/sp3 ...
1
vote
0answers
30 views
Which one is the correct molecule of the given properties of IR Spectroscopy?
$\ce{CH3CH=CHCO2CH3}$
$\ce{CH3COOCH=CHCH3}$
$\pu{2950 cm-1}, \ \pu{2870 cm-1}, \ \pu{1740 cm-1}$ are the observed peaks.
No peaks observed $\pu{1700-1500 cm-1}$.
The formula of the molecule is $\ce{...
2
votes
0answers
100 views
What are the alternatives we have to the VEDA 4 vibrational energy distribution analysis software?
Said software is very useful when you need to assign the peaks in vibrational spectra to different vibrational modes found in a hessian calculation for a given molecule, as described in Jamróz, Michał ...
2
votes
1answer
48 views
Do the spectra of compound materials combine linearly with respect to the ratios of the constituent compound spectra?
My question stems from reading this article on the FTIR spectrum of oil that has been mixed with various contaminants.
If one has the spectrum for the original uncontaminated oil and the spectrum for ...
1
vote
0answers
419 views
Aromatic Stretches C=C in Salicylamide
I want to ask a question about the C=C streching modes of Salicylamide.
I was presented with the following spectra and asked to comment on the bonds causing the peaks.
I identified the molecule ...
7
votes
1answer
378 views
Why does the binding of DMSO to metal via the S atom (k-S) strengthen the S=O bond?
So, DMSO (dimethyl sulfoxide) can form metal complexes in both $\ce{\kappa-O}$ and $\ce{\kappa-S}$ mode i.e. binding with the oxygen or the sulfur respectively. The general explanation given is that ...
2
votes
1answer
68 views
Frequency region and "uncoupled oscillators" in vibrational spectroscopy
I am currently studying the textbook Infrared and Raman Spectroscopy by Larkin. In the first chapter of the textbook, the author presents the following table and accompanying explanation:
The ...
0
votes
1answer
67 views
Near-IR spectroscopy measures the broad overtone and combination bands of some of the fundamental vibrations (only the higher frequency modes)
I am currently studying the textbook Infrared and Raman Spectroscopy by Larkin. In the first chapter of the textbook, the author opens (probably prematurely) with the following statement:
Near-IR ...
3
votes
2answers
266 views
H-NMR with 10H integration?
I have the following two spectra (IR and 1H-NMR) see below.
The chemical formula is: C16H16O2
Thus DBE = 9
My approach:
From the IR, I can see that there's no broad peak around 2500-3300, thus I ...