Questions tagged [ir-spectroscopy]

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

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In rovibrational spectra, when exactly is the Q branch forbidden?

I'm aware that the Q branch ($\Delta j = 0$) is usually not observed in rotational-vibrational spectra of diatomic molecules in the gas state, however, I've heard different things about when exactly ...
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171 views

FT-IR background lines

I started doing IR spectroscopy a few months ago and have run into the following problem: Here's the IR background that everyone knows and loves: CO2 peaks in the middle, water lines on either side. ...
5
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1answer
623 views

What is the signal at around 2090 wavenumbers in the nitroguanidine FTIR spectrum?

There is a signal at around 2090 apparent in the FTIR spectrum of nitroguanidine from Sigma-Aldrich (first image). It's also apparent in FTIR spectra we've taken in the lab (second image), but when ...
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115 views

Why does the binding of DMSO to metal via the S atom (k-S) strengthens the S=O bond?

So, DMSO (dimethyl sulfoxide) can form metal complexes in both $\mathrm{\kappa O}$ and $\mathrm{\kappa S}$ mode i.e. binding with the oxygen or the sulfur respectively. The general explanation given ...
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35 views

Ozone cross-section in the near-infrared

I am searching for ozone absorption cross-section in the wavelengths range 1.1 μm to 10 μm. So far I looked in the following databases: HITRAN Max-Planck Institute for Chemistry Mainz and of ...
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54 views

How to effectively induce the bending motion of carbon dioxide?

I would like to know how to effectively induce the bending motion of $\ce{CO_2}$ with femtosecond IR lasers. In other words, how to effectively populate bending vibrational states in $\ce{CO_2}$ ...
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0answers
1k views

Why do electronegative heteroatoms increase C=O stretching frequency (bond strength)

Why does a more electronegative heteroatom (i.e. $\ce{Cl}$ or $\ce{O}$) increase the stretching frequency of a carbonyl? I'd suspect it's that they donate their lone pairs and we end up with a ...
2
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1answer
77 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 ...
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0answers
72 views

CO2 IR extinction coefficients near the 15 micrometer band

I have searched multiple times for a spectrum or a table of the gaseous carbon dioxide Lambert-Beer extinction coefficients in the IR Earth thermal region. All I found was absorption spectra. Is ...
2
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0answers
2k views

What is the peak at 3200 cm⁻¹ in the IR spectrum of Benzocaine?

Benzocaine has the following IR spectrum: and here is it's structure: From what I understand: The two leftmost peaks are the antisymmetrical and symmetrical stretchs of the amine group. Just before ...
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93 views

Why is the Infrared spectrum usually drawn using transmittance rather than absorbance?

Infrared radiation can be used to identify compounds but I noticed that the spectra are usually drawn using percentage transmittance rather than percentage absorbance . Why is that ?
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156 views

Spectral database in the UV-Vis/NIR and IR regime

I'm searching for a bunch of spectra (some tens), preferably with intense bands in the Vis spectrum, to play around with (calculating chromaticity, etc.). They should range from 250 nm to 2500 nm (UV-...
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142 views

Creating an IR Spectrum using Gaussian ADMP Calculation

I have a Gaussian 16 trajectory for a small cluster of water molecules carried out with ADMP technique. I was wondering if anyone knows how to compute the IR spectrum from the information in the ...
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31 views

Trend in the infrared stretching of molecular hydrogen to group 8 transitions metals?

While going through old notes, in relation to the Dewar-Chatt-Duncanson model, it states that the stretching frequency for $\ce{N2}$ to the group 8 transition metals ($\nu(\ce{NN})$) proceeds as: \...
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2k views

How to tell if a vibrational mode in benzene is IR and/or Raman active?

Consider the vibrational mode that corresponds to the boat-like bending of a benzene ring. Is it (i) Infrared active? (ii) Raman active? This question was asked in an assignment in my college. ...
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287 views

S-N bond IR vibrations

I am working on organosulfur compounds where i have S-N bonding, according to literature it might be having an ir vibration of 1100cm-1, could anyone confirm it with reference. (the complete bonding ...
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13 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 ...
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22 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 ...
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0answers
29 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{...
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109 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 ...
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58 views

Increase of peak intensity in case of hydrogen bonding

Typical motif in case of hydrogen bonds is charge transfer from electron rich acceptor Y to (usually) anti-bonding X-H σ* orbital. If so, the X-H bonding distance increases, bond weakens, stretching ...
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30 views

Alkyl insertion with cobalt and CO

Reaction of $\ce{(Cp)Co(Me)2(CO)}$ in the presence of excess $\ce{CO}$ yields two different organic products, $\ce{A}$ and $\ce{B}.$ The only metal-containing product is $\ce{(Cp)Co(CO)2}.$ The IR ...
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37 views

Is there a simpler way to detect alcohol in a blood sample using IR spectroscopy?

I have seen all sorts of ways to detect alcohol using NIRS (Near InfraRed Spectrscopy) or FTIR, but they are all quite complicated in that they are using and analyzing a very wide spectrum. In ...
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768 views

Calculation of average bond length from force constant and IR absorption?

I need some help beginning a problem set problem (just want hints, I'd like to figure it out myself). The problem gives me the IR absorption for a diatomic, as well as the force constant for the ...
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93 views

Absence of anti-Stokes line in Raman spectrum

If we have a molecule 1H-25X which shows a band at $3000~\mathrm{cm}^{-1}$ in the IR spectrum and you want to record a Stokes and anti-Stokes Raman spectrum with a laser of 1000 nm, why is the anti-...
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64 views

Need help with an IR spectrum (polymer identification)

I have been given an unknow polymer and I have to identify it. DSC measurements showed no glass transition (which means it's below room temperature) and a melting temperature at around 100-120°C. So,...
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136 views

Which bands are considered significant in the fingerprint region of IR spectra?

I'm currently writing my characterisations for the experimental section of my dissertation and can't decide which peaks from the fingerprint region of my IR are worth reporting. Is there a threshold ...
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100 views

Theoretical limits of (NIR) spectroscopy for quantitative analysis

Edit (months later): In hindsight, I was asking about the theoretical limits of multivariate curve resolution (see Lawton & Sylvestre: Self-modeling curve resolution) in chemometric applications. ...
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15 views

availability of database for vibrational spectroscopy

is there a database for vibrational spectrums of molecules available? i have recently started working with fragrant molecules and I am interested in their vibrational spectrums. i am limited by the ...
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53 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) ...
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20 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 ...
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29 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 ...
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372 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 ...
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386 views

Distinguish 1-bromobutane and 2-bromobutane with IR

How can I distinguish 1-bromobutane and 2-bromobutane by their IR spectrums? In the 1-bromobutane spectrum I think the $\ce{-CH3}$ peak is shorter, but I don't know if that is actually reasonable or ...