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.
636
questions
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Effect of transition energy gap and frequency of microwave on appearance of CW EPR spectrum
Consider continuous-wave EPR for species with only one unpaired electron in the following argument.
The interaction energy in the presence of external magnetic field of strength B is given by
$$E = Bg\...
4
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3answers
95 views
+50
Using a H NMR spectrum to determine the structure of a protein supplement
This question is about the H NMR spectrum of creatine.
Creatine is a supplement taken by athletes to increase body mass. Recently, supplements containing derivatives of creatine have been marketed. ...
2
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1answer
26 views
Photodissociated iodine laser and population inversion
Iodine molecules ($\ce{I2}$) can absorb in the visible region and dissociate into $\ce{2 I^.}$ radicals. One of the I atoms is in ground electronic state $\mathrm{^2P_{3/2}}$ and the other I atom is ...
2
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1answer
43 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 ...
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0answers
38 views
What is dispersed fluorescence spectroscopy?
There's quite a few papers mentioning the use of dispersed fluorescence spectroscopy (such as this, or this), but I cannot find any explanation to what dispersed fluorescence spectroscopy is. What ...
4
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0answers
23 views
How to determine which levels correspond to each other in LS coupling and jj-coupling?
In the LS coupling scheme, L, S and J are good quantum numbers; whereas in jj-coupling scheme, j1,j2 and J are good quantum numbers. I have learnt how to get the term symbols for LS coupling, and for ...
4
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0answers
42 views
How to determine the source of sub-nm periodic error in NIR spectra
I've run into an issue collecting measurements on deionized water in the $1050-\pu{1200 nm}$ range. To determine the sensitivity of my spectrophotometer in this range, I've acquired measurements on ...
1
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0answers
85 views
How to draw molecular orbital diagrams for protonated/deprotonated methyl red?
Give a molecular structure-based explanation for the differences in the UV-Vis
spectra in I and II. Use detailed MO schemes for A and B for illustration. (12 marks)
Does the double bond of N=N, C=O ...
7
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1answer
153 views
Why No Change in Polarizability in Asymmetric Stretch?
In order for a molecule to be Raman active, there must be a change in the polarizability, meaning that there must be change in the size, shape or orientation of the electron cloud that surrounds the ...
1
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1answer
51 views
Does using same calibration curve for chemical analysis introduce correlation in sample error/uncertainty values?
I am using a hypothetical case to explain my question
Let us consider a chemical analysis method A (using a certain instrument), which is used to quantify the value of a particular species b. ...
0
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0answers
22 views
Negative DBE/Degree of Hydrogen Deficiency?
I tried calculating the Index of Hydrogen Deficiency for C6H15SiCl, and I get negative one. I get this value by subtracting the number of chlorine and hydrogen atoms from that of the carbon atoms, and ...
0
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0answers
21 views
Why hydrogen gas tube produce hydrogen atomic spectrum
To measure the atomic hydrogen spectrum people often uses hydrogen gas tubes as light source.
Since the gas in the tube is the molecule $H_2$ , why we obtain the spectrum of atomic hydrogen?
My guess ...
1
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0answers
25 views
vacuum pack of a substance/substrates
What equipment can I put a substance or substrate under vacuum pack?
After buying this SERS silver substrates (which can rapidly decay in air). I need to immediately put them in vacuum packaging or ...
0
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1answer
37 views
Will Raman photon counts/Spectral resolution increase if laser beam becomes parallel? [closed]
Most Raman spectrometer has the laser converging into focus with the sample at center like this.
Usually how many millions of H2O atoms will be covered by one spot size?
What will happen if the laser ...
3
votes
0answers
57 views
Why do molecules showing a pure rotational spectra require a permanent dipole?
I understand that pure rotational spectra only exist for molecules which have a permanent dipole moment. The common explanation is "so that they can interact with the E-field of the incoming ...
2
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0answers
30 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 $...
2
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0answers
36 views
Can you do SERS without a Raman microscope?
Surface-enhanced Raman spectroscopy or surface-enhanced Raman scattering (SERS) is a surface-sensitive technique that enhances Raman scattering by molecules adsorbed on rough metal surfaces or by ...
3
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0answers
32 views
What plastic is this? (Raman scan)
I can't recognize the Raman spectrum of this plastic.
It's not in the common plastics raman spectrum.
It is plastic adaptor for connecting sediment filters. Anyone got idea or recognize what kind of ...
9
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4answers
1k views
Is it safe to look at a mercury gas discharge tube? [closed]
As part of a chemistry course, I recently observed a demonstration in which the instructor electrified a mercury gas discharge tube (the tube looked something like this image). The glow from the tube ...
2
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0answers
34 views
1,5-Pentanediol MS
I'm having troubles assigning the signals m/z = 41 and 56 of the compound 1,5 pentanediol. I tried the basic fragmentations (McLafferty, loss of OH radical, etc.) but I can't figure the structure of ...
1
vote
0answers
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 ...
1
vote
2answers
61 views
Raman signal of black matte object
This is the raman spectrum of the black cap:
I was expecting it to be Polypropylene but the peaks didn't match in wave numbers. Anyone got idea what kind of plastic has that peaks on the side of 1500?...
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0answers
20 views
Alternating heavy metal materials analysis
If someone had a material that was made of alternating heavy metals (ABAB) and each layer was 1 micrometer thick, would an electron beam be able to displace electrons in the lower layers? If these ...
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0answers
20 views
Analyzing alternating metals in a polymer matrix with 1 micrometer depth and only 10% metal
This is a theoretical question that I am struggling to get started on for a seminar discussion. If you were attempting to design an instrument with all the basic components (source, analyzer, detector,...
1
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1answer
33 views
Is the Hydrogen spectrum only an emission spectrum?
In a statement question it was stated that hydrogen spectrum is an emission spectrum and the scheme considered it to be ture. But my argument is that it can be both emission and abosorption spectrum. ...
0
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1answer
39 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?
3
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0answers
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How would you examine samples of rocks using a handheld spectrometer?
My friend has an old spectrometer set that his father used to own and we are trying to figure out how to use it. Asking his father about it is not an option unfortunately.
The box contains a handheld ...
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2answers
70 views
Implications of the excitation spectra
The fluorescence excitation spectra show the change in fluorescence intensity as a function of the wavelength of the excitation light.
I'm interested in the certain physical implications of the above.
...
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0answers
33 views
Point group specific definition
Does the term only refer to molecules that have the same symmetry elements or exactly the same symmetry operations. Online I see that its the same symmetry operation however my professor's slides show ...
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0answers
16 views
For Fe2O3 what could an XPS peak at 711.9 eV mean
For an XPS spectra of Fe2O3 film on graphite there are peaks at Fe 2p1/2 = 724.2 eV and Fe2p3/2 = 709 eV but there is another peak at 711.9 eV that I can't identify. Any ideas on what this might be ...
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0answers
17 views
What are the advantages of using ellipsometry over AFM to determine film thickness?
I am trying to understand why one would chose one over the other and I am struggling to understand this since both are non destructive. I know AFM can only go at 5 nm but other than that I don't see ...
2
votes
1answer
64 views
Why would Auger electron detection have potential for higher spatial resolution than EDX
I understand that Auger electrons are emitted when an electron falls from a higher energy level to a open inner shell and EDX uses electrons that fall from outer shells when an inner shell is kicked ...
1
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1answer
136 views
Plotting the data using Beer-Lambert law [closed]
For the spectroscopy lab we had a stock dye ($\pu{1.00E-4 M}$ Erioglaucine Blue) that we had to dilute. We had to dilute $\pu{1 mL},$ $\pu{3 mL},$ $\pu{5 mL},$ $\pu{8 mL},$ and $\pu{10 mL}$ in $\pu{...
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0answers
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In SAXS experiment, you observe strong Bragg peaks at q values of x, y and z. What are the d-spacings of the corresponding diffracting planes?
If d=2pi/q
then would it simply be that
d=2pi/x, 2pi/y and 2pi/z?
This feels to simple and i feel like maybe some version of the 4pisin(theta)/lambda equation should be here soemwhere but I cant ...
3
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0answers
49 views
Mechanism of decomposition of alkali metal halides in flames
A student recently asked an interesting question What happens when KCl is introduced in the Bunsen flame?. This apparently simply question led me to an interesting debate. We all know that emission of ...
5
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2answers
603 views
What is happening when KCl burns in a bunsen flame? [closed]
I did the experiment to qualitatively observe the different colours given off by different salts when placed in a flame.
But what is actually happening to the salt ?
Take $\ce {KCl}$ for example.
Does ...
1
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0answers
32 views
How is a photoelectron spectrum assigned?
The photoelectron spectrum of a given molecule is commonly used as experimental evidence of the energy ordering of molecular orbitals (See here:
10.4: Photoelectron Spectroscopy, and many other ...
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1answer
48 views
Is acetylene IR active? [closed]
I've a very straight forward question, I'm confused because I've been told that a atom which has a oscillating transient/permanent dipole is IR active. But there are few asymmetric stretching/bending ...
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0answers
52 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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0answers
30 views
Statistical methods used for testing the homogeneity of the sample
So, if I have multiple FTIR spectra each taken on different location of the sample and averaged from ~20 spectra, how can I check if the sample is homogeneous, i.e., if there are statistically ...
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0answers
36 views
How is Pi antibonding orbital more polar than Pi bonding orbital?
While reading about the solvent effect on electronic transition in ESR spectroscopy, I found it written somewhere that the pi anti-bonding orbitals are more polar compared to pi bonding orbitals.
Can ...
1
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0answers
38 views
Photoluminescence Spectra of Solids
What information can we gain with the photoluminescence spectra of solids? The bandgap can be determined for example, but are there any other useful properties we can learn? I care about this in the ...
1
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1answer
75 views
Determining electronic configuration [closed]
One writes the electronic configuration in terms of shells, spdf subshells, orbitals, and spin of electrons. There are exceptions to principles we know. How does one confirm that the way of writing is ...
0
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1answer
23 views
Difference in peaks in EDS and XPS spectra
I have been reading some papers on XPS and EDS and I saw that there's a difference between the width of the peaks (of the same material) in XPS and EDS. Is the reason for this difference because of ...
2
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1answer
91 views
Detectable elements using flame AES
I've been looking for extra information concerning flame atomic emission spectroscopy. I need a clear overview of which elements are detectable with this technique, but I can't find anything because ...
2
votes
1answer
121 views
XPS/EDS vs FTIR/Raman [closed]
So I have been studying the four methods the past couple of weeks. To my understanding, XPS is a very surface-sensitive technique. It can give information about the composition of the surface but also ...
1
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1answer
115 views
Can you measure an IR spectrum of a sample inside a glass vial?
If I have a sample of some compounds dissolved in water inside a glass vial (let's say quartz). Would it be possible to get a usable measurement through this glass vial without too much absorption by ...
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0answers
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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0answers
78 views
Solving the Schrödinger equation for a rotating triatomic linear molecule
This source is showing that solving the Schrödinger equation for a triatmoic linear molecule yields the same formula for the rotationaI quantum states $BJ(J+1)$ as for dipoles.
For dipoles, the total ...
2
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1answer
53 views
Overview of material characterization methods
I have been searching for quite some time now, but I feel like it is impossible to find some sort of chart where I can determine which characterization method (microscopy, spectroscopy, ...
