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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Is it true that “Voigt Circuit” would be able to be fitted to various electrochemical impedance spectra?
"Voigt Circuit" which is a series combination of Voigt elements (i.e. parallel RC's), is commonly used for Kramers-Kronig relations checking; and as I imagine it is generally believed to be able to be ...
5
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1answer
2k views
Spectrometer vs Spectrometry vs Spectroscopy
How do you differentiate between the three?
I read that "Spectrometry deals with the measurement of a specific spectrum. There are four primary types of spectrometers:
Mass spectrometry 2. Neutron ...
8
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3answers
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How to explain the discrepancy between the calculated absorption wavelength within the particle in the box theory and the observed wavelength?
The experimental observed wavelength for this molecule is 425 nm.
We are supposed to estimate this wavelength theoretically using this equation (energy change in a 1D box), where $N$ is the number of ...
4
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1answer
104 views
Timescales in Chemical Analysis
Has anyone seen a comparative list of typical run times of the techniques used in analytical chemistry? I am making a list of rough timescales of analytical techniques (for a slide). Assume that the ...
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0answers
142 views
Why is absorption spectrum of beta-carotene different from Zeaxanthin?
Here are the molecular structures of beta-carotene and zeaxanthin
These molecules only differ in the OH groups and the conjugated backbone length is exactly the same. I read that the absorption ...
10
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2answers
253 views
Radiofrequency transmitter in an NMR experiment: Is there an involvement of (electromagnetic) radio wave?
A student in Chemistry StackExchange asked the effect of radio waves on matter, which led to an interesting set of arguments by some users. It was pointed out that in a proton nuclear magnetic ...
0
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0answers
34 views
Using MP-AES, can I accurately say I've found a metal concentration on one wavelength and not another?
I've been given the opportunity to use an MP-AES for metal detection. I'm testing traces of metals in plants. The plant matter is digested so I have a liquid solution, I expect there to be a lot of ...
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0answers
37 views
Why is the iron inter-system crossing non-negligible at high temperatures?
Inter-system crossing (ISC) is a radiationless process involving forbidden transitions between singlet and triplet state. These are more common with heavy atom molecules, so I understand that ISC is ...
6
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3answers
421 views
The concept of normal coordinates of a molecule
Sometime ago I had posted the What is the origin of "normal" in normal coordinates and normal modes? in math & sci history problems. Nobody was sure for the reason for using the word normal there -...
2
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1answer
113 views
In Flame Emission Spectroscopy, what part of the flame is used to measure the concentration of the analyte?
Flame Emission Spectroscopy is an analytical measuring device that relates the intensity of the emitted light relative to to the concentration of the sample.
As I am reading an article about FES, I ...
6
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0answers
149 views
How to extract force constants for normal modes from ORCA?
I am following the computational method described in Scientific Reports.[1] Where the authors analyze the contribution of each excited state normal-modes to the shift of the transition energy. For ...
10
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2answers
401 views
Terminology of atomic spectroscopy: Difference Among Term, States and Level
In A Primer on
Quantum Numbers and Spectroscopic Notation
Contents, the concept of a term and level is described as
a) The level is the set of 2J+1 states with specific values of L, S,
and J. ...
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0answers
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 Ļ* orbital. If so, the X-H bonding distance increases, bond weakens, stretching ...
0
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1answer
96 views
Doubt in a question related to electronic transitions in Bohr's orbits
Question
In Bohr series of lines of hydrogen spectrum, the third line from the red end corresponds to which one of the following inner-orbit jumps of the electron for Bohr orbits in an atom of ...
3
votes
1answer
507 views
Term symbols for nitrogen: determining J
I'm trying to figure out what terms are possible for nitrogen with the electron configuration $\ce{[He] 2s^2 2p^3}$. There is an old question on StackExchange and the corresponding answer was a great ...
16
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1answer
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Interpretation of TD-DFT results
For the first time I'm doing TD-DFT calculations (wB97XD functional) in Gaussian 09 for an open-shell system and the results look like the hell of a mess for me. The molecule is rather big, so I ...
0
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1answer
1k views
Raman Spectrum of Water
This is the Raman spectrum of water. There is $\pu{1635 cm-1}$ Raman peak corresponding to $\ce{HOH}$ and $\pu{3410 cm-1}$ Raman peak corresponding to $\ce{OH}$. But why is there general nonzero ...
1
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1answer
125 views
Different shapes of fluorescence spectra in Raman
Note: I haven't owned any of these spectrometers. I'm asking so I can decide whether to buy 532nm or 785nm wavelength raman to probe molecular structure (especially solutions) and I'm concerned about ...
3
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1answer
134 views
Is there a known relation between the diffusion of a molecule and the diffusion of the reactants?
I have a plasma consisting of elements A and B (which have a similar mass). These elements can react to form molecules AB.
$$
\ce{A + B -> AB}
$$
Now if my plasma or gas is expanding based on ...
3
votes
1answer
330 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 ...
3
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2answers
338 views
Quantify the effectiveness of baseline correction in Raman spectra
I've produced several thousand Raman spectra using hyperspectral imaging techniques. These suffer from significant fluorescent interference which produces a curved, sloped baseline.
Using Matlab, I ...
3
votes
1answer
176 views
Difference between relaxation and resonance leading to an absorption spectral feature?
I need help understanding the physics behind this insightful comment below the question Does water really have strong EM absorption at 3 kHz in solid and 2 GHz in liquid? Why the huge shift?:
...
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0answers
35 views
Determine the velocity of the O fragment after the dissociation
A $\ce{SO3}$ molecule is radiated with light with a wavelength of $\pu{193 nm}$, which results in photodissociation.
$\ce{SO3} + \text{photon}(\lambda=\pu{193nm})\ce{-> SO2 + O}$
It is measured ...
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0answers
23 views
How can I know the composition of a gas pocket entrapped in a plastic sheet? [closed]
I have a 1Ā mm thick plastic sheet, the plastic is not opaque.
Some gas pockets, I would say some bubbles, are inside the sheet; the size of the bubbles is about 1Ā mm.
What methods are available to ...
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4answers
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Why are some molecules unable to absorb infrared radiation?
Methane $\ce{CH4}$ is symmetrical and non polar, and so is oxygen $\ce{O2}$. But $\ce{O2}$ doesn't absorb IR. Why is that? People say that if a molecule can change its polarity then it will absorb IR, ...
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0answers
53 views
Does something like a fluorescent foil or a fluorescent film exist?
During my experiments I want the emitted laser beams to come back with a different wavelength than the original wavelength using a fluorescent foil or fluorescent film.
The laser I'm currently using ...
3
votes
1answer
41 views
How appropriate/adaptable is HPLC for in situ sample analysis on Titan?
I have a limited background in chemistry (nothing beyond general Chem 2), so I am asking for help with a group project. We have two chemists on our team, but communication is limited at the time and I ...
4
votes
1answer
127 views
Why are there only 6 series (Lymen, Balmer, Paschen, Bracket, Pfund and H.Davy) in the hydrogen atomic spectrum? Why can't there be more? [closed]
The Balmer series, for example, is formed when the electron jumps from $n_2 = 3, 4, 5, \ldots, ā$ to $n_1 = 2.$
The Humphry Davy series (The last series is formed when electron jumps from $n_2 = 7, 8,...
5
votes
1answer
70 views
What drives vibrational cooling in an excited stated?
As we excite a molecule from its ground state, $S_{0,v=0}$, to some excited state in a higher vibrational state, i.e. $S_{1,v'=3}$, what drives vibrational cooling within that excited state manifold (...
0
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1answer
29 views
Soluble compounds to absorb radio-frequency electromagnetic radiation
Are there any soluble compounds capable of absorbing radio-frequency or long microwave radio-frequency electromagnetic radiation? I have noted that metals are often used to absorb these signals, but ...
5
votes
1answer
122 views
Finding identities of diatomics from Spectroscopy and Mass Spec Data
Let's say I have a sample of 2 (assumingly different) diatomics A and B.
Through spectroscopy I found the data below:
For molecule A:
$$\begin{align}
B&\approx2.17690\ \mathrm{cm^{ā1}}\\
D&\...
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4answers
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Why is wavenumber used in IR spectroscopy rather than wavelength?
In IR spectroscopy, the $x$-axis is used to represent wavenumber, in $\mathrm{cm^{-1}}$. Why is wavenumber, equal to $1/\lambda$, used in place of wavelength, which is simply $\lambda$?
Sources Iāve ...
8
votes
3answers
484 views
Why not use all the colours in colorimetry?
Colorimetry (and it's cousin visible-UV spectroscopy) is a form of chemical analysis that works by sending visible light of one wavelength through the sample. It then analyses how much of the light ...
2
votes
3answers
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Effect of dopant size on XRD peak shift
If we add an impurity atom (doping) to the crystalline struture of another material and take the XRD of the doped material what kind of peak shift can we expect. For the better description of my ...
3
votes
1answer
441 views
AAS background correction with Zeeman effect
I've found here the explanation to how Zeeman effect can be used for background correction. I understand everything up to this part:
"When light is polarized parallel to the field, both atomic and ...
4
votes
2answers
26k views
Why is the carbonyl IR frequency for a carboxylic acid lower than that of a ketone whilst an ester is higher than a ketone
The approximate stretching frequencies are as follows:
Acid: $1710$, Ketone: $1715$, Ester: $1730$ (all $\mathrm{cm^{-1}}$)
This would seem to suggest that the acid decreases the carbonyl bond ...
6
votes
2answers
307 views
Tabulated absorption spectra of greenhouse gases?
Are there any free sources of tabulated absorption spectra of greenhouse gases from UV/Vis to far infrared (say 70 micrometers)?
This link shows the net absorption over the whole atmosphere (at least ...
3
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2answers
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Why should AAS use element lamps?
AAS (Atomic Absorption Spectroscopy) is a quantitative analytical technique used to measure very small concentrations of ions in substances. The main idea is that the sample is atomised in a flame and ...
2
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0answers
33 views
Nice textbook illustration of microwave spectrum for a nearly free internal rotation?
Is it possible to find a nice textbookish example of experimental data for an internal rotation of a molecule, in which the rotation is nearly free? For example, 1-butene is supposed to have a nearly ...
2
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0answers
75 views
Possible ionization and fragmentation of chemicals
Is there any generic method where I can know/calculate/generate the possible ionization and fragmentation of a specific chemical, for example, hydrogen chloride and water?
This question is actually ...
5
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2answers
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Proton NMR chemical shift of water peak in different solvents
Why does the water peak appear at different chemical shift values (ppm) in different solvents in proton NMR spectra? For example, the water peak in DMSO-d6 appears at nearly 3.33 ppm, but the same ...
1
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1answer
23 views
Taking a procedure for ICP and adapting it to use with AAS
I was reading a paper regarding metal detection and they gave their procedure for an acid digest of a soil sample which was then analysed by ICP-OES.
They used nitric acid, hydrogen peroxide and ...
16
votes
1answer
2k views
Using a gas stove instead of Bunsen burner for a flame test?
In all chemistry labs we use the Bunsen burner. What's the difference between it and a good old gas stove used in home? Can the stove also be used to get positive flame tests for some cations (like $\...
3
votes
1answer
211 views
Can anyone help me with this question on vibrational modes of free base porphyrin (C20H14N4)?
4 a. The structure of free-base porphyrin $(\ce{H2P}$, chemical formula: $\ce{C20H14N4})$ is shown below. Given that this molecule belongs to the $D_\mathrm{2h}$ point group (character table given ...
2
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1answer
38 views
What interesting things can be seen in spectra between 400-700nm?
The visible spectrum (400-700nm) tends to give a very blurry spectral picture, as it is not a wide band relative to the typical peak width of features you can find there. Further, the vibrational ...
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0answers
36 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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0answers
60 views
Software for computations of rovibrational states' energies and corresponding spectroscopic constants in diatomic molecules
I need to compute rovibrational energy levels and also the spectroscopic constants, especially $\omega_e$ to compare my results with other papers.
So far I've tried LEVEL16, which seems very ...
1
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1answer
184 views
Binding energy question [closed]
The electrons in the 1s orbital of chlorine have a binding energy of 273 MJ/mol, but the 1s electrons in sulfur have a binding energy of 239 MJ/mol. Why is this?
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0answers
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How to calculate spectral overlap integral using spreadsheets?
I need to calculate the spectral overlap integral for the emission spectrum of coumarin 334 and the absorption spectrum for rhodamine, using spreadsheets (MS Excel).
Following the theory of ...
3
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1answer
126 views
Franck-Condon factors in photoelectron spectroscopy
Franck-Condon factors have been used to predict / assign the vibrational structure of photo-electron spectra.
$FCF=|\langle\psi''_{vib}|\psi'_{vib}\rangle|^2 = |\langle\psi''_{vib,1}\psi''_{vib,2},\...
