Stack Exchange Network

Stack Exchange network consists of 174 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

Questions tagged [ir-spectroscopy]

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

0
votes
2answers
40 views

Infrared Spectroscopy of N2O [closed]

Would you be able to identify the stretch and bend in the spectrum? I can not find much information about the $\ce{N2O}$.It's solved, does anyone know the symmetry of these vibrations?
2
votes
0answers
28 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 ...
2
votes
0answers
18 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 ?
1
vote
0answers
28 views

structure information form IR and Raman spectra? [closed]

Is it possible to gain the idea of full molecular structure from IR or Raman spectroscopy?
-1
votes
0answers
34 views

why does cyanide's IR spectrum in acetonitrile have two bands in the CN triple bond region?

I wanted to know what the CN stretching frequency of CN- in MeCN so I took a spectrum of tetrabutylammonium cyanide in transmission mode. I expected one band around 2100 but instead I got 3! So I ...
1
vote
0answers
104 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 ...
-2
votes
1answer
33 views

Is there a detailed explanation as to why polarity of a molecule affects the absorption intensity of IR radiation? [closed]

Polar molecules have an electric field due to there being a net dipole moment. The electric field will be stronger with greater polarity. The stronger electric field in the polar molecule will ...
1
vote
1answer
28 views

Determination of Urea and Hydrogen Peroxide in Cow Milk by ATR-FTIR(Attenuated total reflection-Fourier Transform Infrared Spectroscopy) [closed]

I am doing a research on cow milk adulteration. I am checking Urea and Hydrogen Peroxide content in milk by ATR-FTIR(Attenuated total reflection-Fourier Transform Infrared Spectroscopy). I am using $\...
1
vote
1answer
51 views

How do I get Mass spectrometry graph, history, and Infra-red spectroscopy graph for Secnidazole?

My chemistry teacher wants me to create an academic poster for a recently-discovered biologically important organic molecule with chirality that is relatively small and is also recent. Secnidazole (...
2
votes
0answers
37 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-...
2
votes
0answers
58 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 ...
0
votes
0answers
46 views

Why does the bending vibration of H2O span the A1 (rather than B1) irreducible representation?

Defining the $H_20$ molecule as being in the xz plane with the z axis being the principal axis. Why does water have a bending vibration from the $A_1$ irrep and not $B_1$? Since $B_1$ contains the $...
1
vote
1answer
299 views

How to systematically find the reducible representation of a molecule? (eg: XeF4)

I am attempting to use the reduction formula to find the irreducible representation of $\ce{XeF4}$ to determine its IR stretching vibrations. I know the point group of $\ce{XeF4}$ is $D_{4h}$ and have ...
0
votes
0answers
50 views

Beer's law relationship for light scattering at 90 degrees

First-time poster here In Beer's law, the ratio of incident light intensity, $I_0$, to exiting light intensity, $I$, is defined as $\log_{10} (\frac {I_0} {I}) = \epsilon L c$. Then, by rearranging ...
2
votes
0answers
53 views

Where can I find example MS, IR, NMR spectra for teaching molecular spectroscopy?

I am teaching a course on analytical chemistry, and I would like to give my students MS, IR and NMR spectra to practice with. It would be ideal if they could analyze spectra in a more "realistic" way ...
1
vote
0answers
35 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-...
0
votes
0answers
20 views

What is the difference of polarizability and dipole moment? [duplicate]

One is for Raman and the other is for IR. The words both have 'pole', so I often confused each other.
0
votes
0answers
70 views

Effect of C13 vs. C12 reduced mass on specific vibrational modes

I understand that the reduced mass of C13 will be greater than for C12, and therefore its vibrational frequency will be lower, as it is inversely proportional to the reduced mass. However, I was ...
2
votes
1answer
450 views

Differences between Liquid and Solid Infrared Spectrometry [closed]

In general, when should I use liquid or solid IR spectrometry to analyse my compound? What should I expect to see? Would I see higher or lower frequency, broader or narrower transitions? My specific ...
2
votes
1answer
50 views

Origin of broad CO stretch in infrared spectrum of tricobalt cluster

I'm quite confident that the peaks around $\pu{2000 cm^{-1}}$ are $\ce{CO}$ stretches. But I cannot find any reference on that massive broad stretch following the $\ce{CO}$ stretches. Does it have ...
0
votes
1answer
85 views

Why do the unsaturated ketones have C-O bond weaker than saturated ketones? How it is related to resonance structures?

I am studying Infrared Spectroscopy and the book says that unsaturated ketones have a carbonyl group which has weaker bond because it's more single-bond character than single bond because it has these ...
0
votes
1answer
157 views

Stretching frequency of nitro and nitrito

I got the values of the stretching frequency of nitro and nitrito ligands from this webpage. I understand why stretching frequencies are close in nitro and well separated in nitrito. How to explain ...
1
vote
0answers
31 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,...
1
vote
0answers
63 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 ...
1
vote
1answer
483 views

Distinguishing propan-2-ol from ethanol using IR spectroscopy

A question requires me to distinguish between propan-2-ol and ethanol from IR spectra. To me, they both look nearly identical, even though I know both of them contain the same functional group and ...
4
votes
1answer
1k views

Assignment of the IR spectrum of 2,4-pentanedione (acetylacetone)

The IR spectrum is shown here: My assignments so far: The 1728 and 1708 stretches correspond to $\ce{C=O}$ stretches in the keto form - the symmetric/asymmetric stretches respectively. The 3003 ...
1
vote
1answer
167 views

In vibrational spectroscopy, what affect do overtones have on the spectra? [closed]

I've been in a lecture about vibrational overtones in anharmonic oscillators. How would these affect an IR spectrum?
0
votes
0answers
63 views

Why do strongly electronegative atoms increase the double bond character of the carbonyl group?

I was reading Solomon's Organic Chemistry, when I came across the IR Spectroscopy part. The book says that an ester shows a peak at a higher frequency than an aldehyde because the C=O bond has ...
1
vote
0answers
67 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. ...
3
votes
1answer
105 views

Wavelength-dependence of refractive index in internal reflection spectroscopy?

In many literature sources (web example), only a single value for the refractive index is assumed for the infrared element, and another is typically assumed for the sample substance. However, should ...
2
votes
0answers
26 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: \...
2
votes
2answers
1k views

Why does an OH bond absorb a higher frequency than a CH bond?

I'm wondering why a bond between an O and an H is going to absorb a higher frequency than a bond between a C and an H (any hybridization). O is heavier than C in terms of atomic masses, and I'm ...
1
vote
0answers
29 views

rovibrational spectroscopy: why do intensities of rotational lines increase with J? [closed]

how and why do the intensity of rotational lines change with J value? in the simplest terms possible please
1
vote
2answers
3k views

O-H infrared band dependence of alcohol concentration in water

With regard to IR spectroscopy, how would the O-H band change as an alcohol solution was diluted with water? I am referring to any alcohol, but for the sake of example we can use ethanol. I think ...
13
votes
1answer
807 views

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 ...
0
votes
0answers
74 views

Are the spectra of Imidazole and N,N-carbonyldiimidazole equal?

For QC reasons, I measured an ATR spectrum of a substance suspected to be imidazole and then ran a database search in a Sigma-Aldrich library looking for hits. I got two matches: imidazole and N,N-...
3
votes
2answers
59 views

How do IR spectrometers produce light spanning the entire infrared spectrum?

An IR spectrum covers thousands of wavenumbers, typically $\sim 4000$ to $\pu{400 cm-1}$. How are the spectrometers able to generate different wavelengths of light covering this entire range of ...
3
votes
0answers
42 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 $\ce{CO_2}$ ...
1
vote
0answers
361 views

IR spectroscopy in CCl4 Solution v/s Liquid film [closed]

Why there are differences in these spectra ? Which one is more useful and accurate ? What is the significance of using these two different methods ?
11
votes
1answer
362 views

How to determine conformation using IR

In my advisor's Ph.D. research, she used IR spectroscopy to (help) determine the conformation of a compound of interest (its structure is known.) In organic chemistry, I learned about using IR as a ...
7
votes
2answers
156 views

Harmonic frequencies (IR) and basis set size

Usually vibrations (harmonic), derived from harmonic approximations are bigger than for experimental values. The question is, how does this depend on the size of the basis set. Many papers give that ...
3
votes
1answer
387 views

What exactly is the long chain band?

I have progressed quite enough in infrared spectroscopy, and now I'm looking at the spectrum of alkanes in detail. I found out that straight chain alkanes have this long chain band in the spectrum: ...
10
votes
3answers
1k views

Why does the C–C bond have extremely weak absorptions?

My book, Pavia's Introduction to Spectroscopy, tells me this about the infrared spectrum of alkanes: $\ce{C-C}$ : Stretch not interpretatively useful; many weak peaks. This is very interesting. ...
0
votes
1answer
2k views

What do s, m, w, m-w, and w-s mean in the context of infrared spectroscopy?

I am referring to Donald Pavia's Introduction to Spectroscopy, and I found this table that tells about the intensities of the peaks of vibrations of certain bonds. I can't understand what ...
1
vote
1answer
213 views

Where can I find (citable) FTIR spectra of CuCl and CuCl2?

I can't seem to find any published/citable infrared (FTIR) spectra in the 4000-400 cm-1 range of CuCl and CuCl2. Does anyone know of a source available, either free or paid?
3
votes
1answer
208 views

Expected accuracy of experimental IR spectra compared to literature reference

I have a table from a journal which indicated signals of an alpha chitin that I used as theoretical values. I did my own analysis to identify a chitin sample and it had signals that slightly varied ...
1
vote
1answer
136 views

Slight FTIR band intensity changes across several different copper salt spectra: relevant for characterization?

I have several spectra of different samples which are probably all copper (neutral and/or basic) acetate(s) and which are very similar. I present them overlayed and (some of them) stacked: My ...
7
votes
1answer
342 views

Why does nitrous oxide have 300 times the global warming potential of CO2?

Both nitrous oxide and carbon dioxide have roughly the same atmospheric lifetime (nitrous oxide slightly longer), so I thought that it would have to do with the infrared absorbance associated with ...
4
votes
1answer
775 views

Aromatic Overtones

For IR Spectroscopy, I noticed that there are aromatic overtones or "benzene fingers" a bit below the $\mathrm{2200~cm^{-1}}$ region. Why do these occur in IR spectroscopy? And is there any way to ...
-2
votes
1answer
329 views

OH band in IR of propyl ethanoate? [closed]

In lab I combined 1-propanol with acetic acid to make propyl ethanoate. I obtained an HNMR and an IR of the product. The HNMR suggests that the product was successfully synthesized. The IR has the ...