Questions tagged [ir-spectroscopy]
Use this tag for questions regarding the principles and application of infrared spectroscopy.
184
questions
-2
votes
0
answers
23
views
Do we need a standard sample for the interpretation of infrared spectroscopy (IR) results? [closed]
I'm having a problem with the interpretation of the Ginkgo biloba IR spectrum, all of the articles I read never mention if there's a standard spectrum to compare the results with.
Do we need a ...
0
votes
0
answers
22
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 ...
- 13
2
votes
0
answers
32
views
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 ...
- 211
1
vote
1
answer
42
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 ...
- 13
-2
votes
1
answer
38
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, ...
- 265
2
votes
0
answers
93
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 ...
- 367
8
votes
2
answers
232
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 ...
- 348
1
vote
2
answers
112
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 ...
- 119
5
votes
2
answers
96
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 ...
- 53
-2
votes
1
answer
213
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 ...
- 11
3
votes
1
answer
165
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 ...
- 117
6
votes
1
answer
196
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 ...
- 77
2
votes
1
answer
124
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 ...
- 21
0
votes
0
answers
41
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?
- 1
4
votes
2
answers
200
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 ...
-1
votes
1
answer
54
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?
- 15
1
vote
0
answers
59
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 ...
- 4,232
7
votes
1
answer
243
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....
- 5,742
3
votes
0
answers
132
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 ...
- 31
3
votes
1
answer
100
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 ...
1
vote
1
answer
1k
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-...
- 67
2
votes
1
answer
88
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 ...
- 85
3
votes
1
answer
404
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 ...
- 41
4
votes
0
answers
92
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 ...
- 305
0
votes
1
answer
119
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.
...
- 411
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 $\ce{Fe2(CO)9}$. ...
- 91
3
votes
1
answer
57
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 ...
- 1,307
0
votes
1
answer
722
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?
- 35
0
votes
1
answer
696
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 $cm.molecule$).
...
- 517
1
vote
1
answer
154
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) ...
- 746
7
votes
1
answer
524
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 ...
- 39.1k
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.). ...
- 5,647
2
votes
0
answers
86
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 ...
- 151
1
vote
0
answers
102
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, ...
user85551
3
votes
1
answer
867
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 ...
user85551
3
votes
2
answers
680
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....
user85551
3
votes
1
answer
904
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 ...
- 31
2
votes
0
answers
43
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 ...
- 21
0
votes
2
answers
109
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 ...
- 101
1
vote
0
answers
40
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 ...
- 21.5k
-5
votes
1
answer
533
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
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 ...
- 175
3
votes
1
answer
111
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 ...
- 6,218
1
vote
0
answers
19
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 ...
- 181
0
votes
1
answer
329
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 ...
- 577
2
votes
0
answers
86
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 $...
- 215
0
votes
1
answer
111
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 ...
- 607
1
vote
0
answers
44
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 ...
- 243
-1
votes
2
answers
1k
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 ...
- 229
0
votes
1
answer
47
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?
