Questions tagged [spectroscopy]

Use this tag for questions about spectroscopic methods in practice and in theory, especially where more specific tags for the individual method (such as [nmr-spectroscopy] or [ir-spectroscopy]) are not available.

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2
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1answer
333 views

D3d point group matrices

I am trying to construct all the matrices for the point group D3d operations. I find that the matrices of E, i, S6, inverse of S6, C3, and inverse of C3 are easy, but I do not know how to construct ...
6
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1answer
2k views

Relationship between electric dipole moment and polarization?

$$\vec{p}_\text{ind} = \alpha \vec{E}$$ The induced dipole moment is the polarizability times the electric field vector. $$\vec{P}(\omega) \propto \chi^{(1)}(\omega) \vec{E}(\omega)$$ The polarization ...
9
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1answer
281 views

Why do we say “approximation” in the dipole approximation in spectroscopy?

In the dipole approximation, the following relation holds: $$ \hat{V} = -\hat{\mu} \cdot \vec{E}. $$ When we say "approximation", I guess we want to point out that we are dealing with linear ...
2
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1answer
688 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?
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0answers
21 views

Identifying luminescent transitions for lanthanides

Using the ground-state of Eu(III), how can I identify the possible (number of) luminescent transitions from the $^{5}D_{0}$ excited state? I identified the ground-state term symbol for Eu(III) using ...
6
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1answer
363 views

Rotovibrational selection rules for symmetric tops

The selection rules for symmetric top molecules are $\Delta J = 0, \pm1$ and $\Delta K = 0$ for $K \neq 0$ (parallel transition) $\Delta J = \pm1$ and $\Delta K = 0$ for $K = 0$ (parallel ...
1
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1answer
252 views

metal oxide analysis

I am looking in to analytical techniques for a future project. I may have a mixture of metals, i.e. an alloy, which I am thinking XRF spectroscopy would be the best quantitative technique. I could ...
2
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1answer
260 views

Absorption spectrum of Hydrogen molecule in UV region 200 nm - 300 nm (not Atomic Hydrogen)

Can somebody provide Absorption spectrum of Hydrogen molecule? I have searched days for absorption spectrum of Hydrogen molecule in 200 nm - 300 nm UV region and All I got is absorption spectrum of ...
10
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1answer
312 views

Conservation of angular momentum in rotational spectroscopy

In spectroscopy, transitions between rotational energy levels obey the selection rule $\Delta J = \pm1$. The rule follows from the fact that the photon absorbed has an angular momentum of $\pm \hbar$, ...
3
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1answer
194 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 ...
7
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1answer
2k views

What does the peak separation of carbon dioxide IR rotational-vibrational spectrum corresponds to and why?

Spectrum of $\ce{CO2}$ at $2349\space \mathrm{cm^{-1}}$ region For some other molecules (for example $\ce{CO}$) the peak separation corresponds to $2B$ (where $B$ is the rotational constant ...
3
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1answer
140 views

Why is the excitation energy different from the energy difference between the orbitals involved in transition?

Why is the excitation energy different from the energy difference between the orbital from which a electron is excited to the orbital in which the electron is excited to? Consider that the transition ...
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0answers
36 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
6
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2answers
493 views

HOMO Odd, LUMO Even: Why does the affected orbital change depending on the carbon? How are carbons numbered?

While looking at how substituents affect the absorption spectra of molecules, I came across this: Substituents alter the emitted wavelengths of these molecules by affecting the electron densities. ...
2
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1answer
657 views

How can Hydrogen NMR be used to distinguish between these two isomers?

I am having trouble explaining how and why the spectra of these two compounds would differ: I am sure it has something to do with how the protons will couple. In the first isomer (left), the protons ...
2
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1answer
89 views

Compare concentrations using LC/MS

Suppose I run a reaction and then pass the results through LC/MS to find the conversion. One idea could be to compare the peaks of the reactants to the peak of the product. But: MS peak will depend ...
9
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0answers
582 views

Finding the wavelength of maximum absorption of Tartrazine using Fieser-Kuhn

How would you use Fieser-Kuhn rules to calculate the wavelength of maximum absorption for tartrazine? Fieser-Kuhn rules states that: $\lambda_{max}=114+5M+n(48-1.7n)-16.5\ R_{endo} - 10\ R_{exo}$ ...
3
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1answer
123 views

Deduce the possible structure given spectroscopic data for the aromatic compound

For $\ce{C11H13NO}$, I have the following $\ce{^1H}$ NMR data: shift (ppm) 3.00 (6H, s) 6.55 (1H, dd, $J=15.5, \pu{9 Hz}$) 6.70 (2H, d, $J=\pu{8Hz}$) 7.35 (1H, d, $J=\pu{15.5Hz}$) 7.45 (2H, d, $J=\...
3
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1answer
85 views

How can I figure out which coupling constants match which hydrogen?

I am looking for some guidance assigning the $J$ coupling constants to the corresponding hydrogens. Here is my data: I can obviously see that shift 3.56 is for the methyl group. I can also see that ...
1
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0answers
82 views

How does the electron configuration correlate with the emission spectrum of an ionic compound? [closed]

trying to find a way to correlate the electron configuration of an ionic compound (ie. Cupric sulfate, potassium chloride, Cupric chloride, sodium carbonate, strontium chloride) with its emission ...
25
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3answers
4k views

Are the bonding orbitals in methane equivalent - photoelectron spectrum

The low energy portion (the part dealing with the $\ce{2s}$ and $\ce{2p}$ electrons) of the photoelectron (PE) spectrum of methane is reproduced below. (image source) The reaction being examined is ...
9
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0answers
3k views

Why do asymmetric stretches occur at higher wavenumbers than symmetric stretches? [duplicate]

I learned that the $\ce{N-H}$ bonds in a primary amine lead to two signals the infrared spectra at $\sim \pu{3400 cm^-1}$, one for symmetrical stretching and another for asymmetrical stretching. For ...
14
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2answers
8k views

Why does the carbonyl group in an acid anhydride have two stretching frequencies?

The carbonyl stretching frequencies for an acid anhydride are approximately $1820~\mathrm{cm^{-1}}$ and $1760~\mathrm{cm^{-1}}$. These are both higher frequencies than a simple ketone owing to the ...
4
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1answer
321 views

Is a spectrophotometric method of measuring the rate of a complex reaction valid?

A few months back I designed and carried out an experiment to measure the rate of the reaction between ferric chloride and copper.The dependent variable was the rate of the reaction; the independent ...
0
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1answer
128 views

Raman activity in sulfur

I was wondering why sulfur is Raman active but other elements (e.g. carbon) are not.
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1answer
804 views

What is the difference between an electron in ground state and an electron in excited state?

What is the differnce between a ground state electron and an excited state electron? Upon excitation what exactly changes about the electron?
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0answers
941 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 ?
14
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4answers
1k views

How do I determine the molecular vibrations of linear molecules?

I know how to do it for just about every other point group, but the $D_{\infty \mathrm h}$ and $C_{\infty \mathrm v}$ character tables aren't as straightforward. In particular, I'm interested in the ...
2
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2answers
3k views

How to calculate the rotational constants for different states from a stick spectrum?

Given a stick spectrum for an unknown diatomic molecule, how do you determine the rotational constants $B_\nu$ for both the excited and ground states given that $$E_{j}=B_{\nu}j(j+1)$$ \begin{array}{...
5
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1answer
340 views

Balmer and Paschen Series

If electron makes transition from, in $H$ atom, $6\rightarrow 2$ (to Balmer), then $\bar{\nu}_{{H}_{6\rightarrow 2}}=x$ (let). Also if electron makes transition from, in $He^{+}$ ion, so that $\bar{\...
1
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1answer
111 views

How can I determine/quantify the presence of boron nitride on a metal surface?

We use micron-grade hexagonal boron nitride (hBN) to coat the surface of bullets that are jacketed in gilding metal. This coating is mechanically embedded/plated onto the surface in order to increase ...
7
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2answers
632 views

Confusion on light absorption by electrons

Say an atom's electron can jump between energy levels n = 2 and n = 3 with x joules of energy. If a light beam of frequency f provides x+y joules (where y is a positive number), that is, more than ...
3
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1answer
107 views

Color difference among oxovanadium species

Why dioxovanadium $\ce{[VO2]+}$ is pale yellow, whereas orthovanadate $\ce{[VO4]^3-}$ is colorless? Both of them should be colorless if we ignore charge transfer for a moment, because in both cases ...
2
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0answers
120 views

Blue shift in UV-Vis of ZnO?

The characteristic wavelength of ZnO is supposed to be ~380 nm. However, in this article1, the peak has been blue-shifted to 214 nm. This is quite similar to my sample where the peak is at 200 nm. In ...
1
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1answer
86 views

Is visible spectroscopy the only non-electronic method of all the spectroscopy method?

Is visible spectroscopy the only non-electronic method of all the spectroscopy method? I know some of the spectroscopy method is possible being used because of electronics.
10
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2answers
2k views

Comparing the experimental and calculated UV/vis spectra for ethene

I am trying to compute UV/Vis absorption spectrum for Ethene using Gaussian 09. I created the ethene molecule in GaussView 5, and cleaned it. Then I optimized the molecule and checked if I got the ...
1
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1answer
67 views

When precessing nuclei absorb electromagnetic radiations, am I supposed to consider the wave nature or particle nature of light?

I decided to peek into the NMR section of my spectroscopy book, and I found out lots of interesting stuff. And along with the interesting stuff, I did come along some stuff that I didn't understand. ...
11
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3answers
2k 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
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1answer
132 views

Absorption HOMO-LUMO, canonical?

So I already asked yesterday about canonical and localized orbitals together with Koopman's theorem where we came to the conclusion that for for example ionization potentials localized orbitals cannot ...
5
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2answers
10k views

Use of water in IR spectroscopy

I am familiar with the process of IR spectroscopy and the preparation of IR samples. However, I am curious as to why you cannot use hygroscopic or protic solvents for IR spectroscopy. Is it just ...
37
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3answers
5k views

A compound that absorbs all visible light

Is there a compound that absorbs all visible light?
3
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1answer
988 views

Calculating the UV/Vis spectrum of perylene

I recently started to do computational chemistry and am now trying to write some basic inputs for important calculations. One, which I guess is quite important to me would be to predict UV/Vis spectra ...
3
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0answers
131 views

Spectra of Methylene Blue

Does the spectrum of Methylene Blue change on prolonged exposure to light? I've studied about the photochemical reactions and about energy transfer reactions. Methylene Blue is a triplet sensitizer ...
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0answers
30 views

Why photons with longer wave length demonstrate more active scatter and transmit that shorter length?

Why photons with longer wave length demonstrate more active scatter and transmit that shorter length? This troubles me to understand why NIR and Infra-Red goes through diffused media when compared to ...
1
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1answer
412 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?
0
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1answer
41 views

How to determine interaction of photon with a hydrocarbon Bixin

Bixin is an apocarotenoid found in annatto with 25 carbons with carboxylic acids at each end of the chain. It is an insoluble orange red pigment. I am interested to study photon interaction with ...
10
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1answer
9k views

Derivation of the Orgel diagram for octahedral d2 complexes

The Orgel diagram for a typical octahedral $\mathrm{d^2}$ complex is shown below: (source: Kettle, Physical Inorganic Chemistry, p 146) I understand that the right-hand half of the graph shows how ...
3
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2answers
213 views

Functionalization of nanoparticles

I want to functionalize silver nanoparticles with thiol group. My question is "how can I find that the thiolated compound is attached to the surface of nanoparticles or not?"
2
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1answer
1k views

Why is the force constant for double and triple bonds approximately double and triple of that of a single bonds?

I am new to spectroscopy, and I am referring to Donald Pavia's Introduction to Spectroscopy. I came across this statement in the book, under the chapter Infrared Spectroscopy: $K$ is a constant ...

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