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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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Why must the beta term in the rigid-rotator PDE take the form J(J+1)? [duplicate]

Here is the partial differential equation for which the solutions Y are are the wave functions for the rigid-rotator (Equation 5.5 in McQuarrie and Simon's Physical Chemistry). $$\sin\theta\frac{\...
Eli Jones's user avatar
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1 vote
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How to get Raman shift frequency values from neutron scattering measurements?

I have read some papers that say that a Kohn anomaly mode is a particular feature of 2H- transition metal dichalcogenides and that the existence of such a mode can be seen in neutron scattering data ...
John's user avatar
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2 votes
1 answer
197 views

Is there a difference between $A_{1g}$ modes and $A_{g}$ modes?

I know that both are totally symmetric and that the '$1$', according to the Mulliken table, refers to symmetry around the $C_2$ axis but I was reading some papers and found that modes were sometimes ...
John's user avatar
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3 votes
1 answer
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Are A1g modes reduced at 180 degrees polarisation in Raman spectra?

I have read that A1g modes are identifiable in Raman spectra by looking at cross-polarised Raman spectra and seeing peaks that strongly reduce in intensity. So essentially, the intensity of A1g modes ...
John's user avatar
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2 votes
0 answers
72 views

Factor Group Analysis of Na2SO4 - Site Group Symmetry

I'm still trying to understand how to construct a factor group analysis for a given molecular point group and the resulting solid state group symmetry. For this I searched for some examples and found ...
Justanotherchemist's user avatar
1 vote
0 answers
55 views

M- 15 Peak of 1-pentene in EI-MS [closed]

This is the spectrum of 1-pentene. And my professor says that the peak M-15 (55) came from this process: But how this is possible, when I tried to prove through mechanism, no one situation match ...
Everson Gomes's user avatar
1 vote
0 answers
32 views

What is the main difference in between PGNAA and PINS?

I understand that both use a neutron emitter to trigger the material being analyzed to emit gamma radiation which is then analyzed to determine the material, but what is the exact difference between ...
Jordan M's user avatar
4 votes
2 answers
229 views

What can be reasons for such anomalies in the IR spectrum of iodoform?

A few weeks ago I collected an IR spectrum of iodoform in KBr as part of a computational chemistry course. For some reason, there is consistently a trough right before every peak, and I am unsure of ...
Simon Joubert's user avatar
12 votes
3 answers
726 views

Reconstruction of NMR spectrum by entropy maximization (MaxEnt)

Currently NMR spectra are generated by Fourier transformation of free induction decay curves from time domain to frequency domain. In the late 60 s-80s some researchers proposed reconstruction of NMR ...
AChem's user avatar
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11 votes
1 answer
3k views

Difference between a "cartoon" flame test and a "real" flame test? How do chemists do flame tests correctly?

This well-received answer to Why does the same electron transition release photons of different frequencies for some elements? begins with the following intriguing passage: I am glad that you updated ...
uhoh's user avatar
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5 votes
3 answers
343 views

Excited states and emission lifetimes

I have some doubts about the nomenclature of the lifetimes. Are singlet and fluorescence lifetimes the same? As well as the triplet and phosphorescence lifetimes? Also, can the triplet/phosphorescence ...
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3 votes
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Regioselectivity in oxo-Diels-Alder reaction

I have one doubt about the dimerization of methacryloyl chloride into the product 3: The dimerized product was observerd around 10-15mol% in different commercial samples of methacryloyl chloride, as ...
Elnani's user avatar
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-1 votes
1 answer
51 views

Analog of chemical accuracy in vibronic energy calculation [closed]

Is there any analog of chemical accuracy in vibronic energy calculation? I understand that the unit is /cm however, probably, I shouldn't expect a given number in that unit as the analog. I am ...
Omar Shehab's user avatar
3 votes
1 answer
213 views

What exactly happen when 532nm laser cause fluorescence in red objects

I hit the above plastic sliding toys with 532nm Laser in a Raman spectrometer and the following are the spectra of each. This is the blue sliding toy showing the right Raman for the plastic. But when ...
Jtl's user avatar
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5 votes
1 answer
409 views

Why does the 1H NMR spectrum of methacryloyl chloride show two singlets instead of two doublets for vinyl protons?

Based on what I have understood, for methacryloyl chloride there is a geminal coupling of the vinyl protons since they are not chemically equivalent. Why are two singlets observed for vinyl protons ...
Elnani's user avatar
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0 votes
0 answers
71 views

Tips on understanding one-bond J couplings in NMR

I have just started a spectroscopy course in nuclear magnetic resonance, which I have loved thus far, but have been extremely puzzled regarding 1J coupling constants. I was wondering if any of you had ...
nking1390's user avatar
-3 votes
1 answer
514 views

Cant figure out whether Lithium or Strontium is in my substance? [closed]

So for uni I got a substance and I have to basically figure out which anions and cations are in it. I get two chances to guess otherwise I get a new substance and have to start from scratch. Anyway ...
user125709's user avatar
0 votes
0 answers
44 views

Searching for electronic spectroscopy reference book

I'm looking for a reference book that will help me describe UV-VIS spectra of organic compounds in terms of Q band, MLCT band, Soret band, and so on. Is something like that available? Thanks
farmaceut's user avatar
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0 answers
94 views

Continuous measurement of urea concentration in water

My colleague and I are working with fertilizers, and we are trying to continuously measure the concentration of urea in water (In situ concentration as function of time). There are two condition that ...
Tensor's user avatar
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1 vote
0 answers
109 views

What are the available cheap proteins that are much less soluble than BSA

Currently, as a beginner, I'm performing solubility analysis (with UV based spectrometry) for practices. The protein I'm using now is BSA. This is widely used and cheap option. I'm now looking for a ...
littleworth's user avatar
1 vote
0 answers
98 views

Calculating Band Gap Energy When Absorption Spectra Shifts with Concentration?

I am not a chemist. However, from some experimental work I have been doing, I have found that the intensity of the spectrum changes with dilution, this makes sense. However, when calculating the band ...
Dr. Ernesto Chinchilla's user avatar
1 vote
0 answers
28 views

Charge Transfer and Multireference Methods

I have read in literature that systems that exhibit "high charge-transfer character" are best treated using multireference/multiconfigurational methods. Why is that? What makes such a system ...
user124272's user avatar
1 vote
0 answers
50 views

Methods to detect iron in highly concentrated ferric sulphate solutions

I’m writing with a query related to reagents used to detect iron in highly concentrated ferric sulphate solutions. I am currently exploring iron detection in both solutions of ferrous $\ce{(Fe^2+)}$ ...
Nicholas's user avatar
2 votes
1 answer
311 views

Creating custom spectra graphs

I wanted to make a few custom spectra graphs for some homework questions I'm assigning. The issue is that the Education Board issued datasheets do not reflect online images. They often say that bonds ...
John Hon's user avatar
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6 votes
1 answer
1k views

Why does band heads arise in vibrational-rotational spectra?

I learn that a band head is a region of maximum intensity due to many lines falling together. It can be determined by differentiating the expression for the R branch. To no avail, I cannot find any ...
user4723's user avatar
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1 vote
0 answers
54 views

Why probability for an atom is fraction for population?

In the canonical ensemble the probability of finding an atom (or molecule) in its $i$-th energy state is given by the Boltzmann factor. This probability is interpreted as the number of microstates ...
Anton's user avatar
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0 answers
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Spectroscopic methods for quantifying peptides/proteins with or without Tryptophan or Tyrosine content

I have several peptides (20-50 amino acids long) which I want to quantify the solubility/concentration in a solvent at certain temperature and pH. These peptides may or may not contain Tryptophan or ...
littleworth's user avatar
1 vote
0 answers
43 views

Electronic vibrational rotational transition of electrons -- for a transition from $\Sigma$ to $\Pi$ how are P and R branches possible?

Suppose we have a diatomic molecule in a $^1\Sigma$ state, and it transitions to an excited $^1\Pi$ state. Note that the total spin of the electrons remains unchanged ($\Delta S=0$) as we can assume ...
Garf's user avatar
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2 votes
1 answer
173 views

NMR spectroscopy nomenclature: induced vs local vs effective magnetic field (B)

This is a simple question but I can't seem to find a place where they use the same nomenclature... I was wondering whether these are all the same thing: $B_\mathrm{induced}$, $B_\mathrm{local}$, $B_\...
lia's user avatar
  • 29
0 votes
0 answers
80 views

A question regarding hydrogen emission and absorption spectrum

I have read in many articles as well as my textbook that when an electric discharge is passed through a sample of hydrogen gas it excites the electrons and glows emitting light.When this light is ...
AJknight's user avatar
5 votes
3 answers
483 views

What is the relationship between Ha and Hb in the given compound, trans-1,3 dichlorocyclobutane. Are they enantiotopic or homotopic?

The question is to find the TOPICITY relationship between Ha and Hb in the given compound, (trans 1,3 dichlorocyclobutane) They seem to be in the same chemical environment, so I tried the ...
Cyclopropanol's user avatar
3 votes
1 answer
948 views

Why am I getting a triplet instead of a singlet on NMR for aryl HH2-group?

I am trying to interpret an $\ce{^1H}$-$\mathrm{NMR}$ spectrum on the molecule 4-amino-N-(2-chlorophenyl)benzenesulfonamide that I produced in a lab session. I have managed to assign all the hydrogen ...
chemstudent's user avatar
-2 votes
1 answer
913 views

Comparison between Atomic Spectrum of Hydrogen and Alkali Metals

I posted a question on Chemistry Stack Exchange a while back. It was related to the naming of atomic orbitals. One of the answers to it mentioned a research experiment. The link to the question is ...
user avatar
0 votes
1 answer
74 views

How to guess the Chemical state in which particular element will be present from XPS data?

Since my last post yesterday, I found some leads and started to analyse my data. But then I started encountering more doubts, questions and confusion. Any help will be highly appreciated and will help ...
wulf's user avatar
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2 votes
0 answers
273 views

Determining chemical state and oxidation state from XPS analysis

This is an call for help! I have performed XPS analysis of my samples to get chemical state in which each element is present. I had given the samples to a third party lab. The operator has provided me ...
wulf's user avatar
  • 93
3 votes
1 answer
456 views

How many elements have been identified for which there are no known spectral lines?

Background: @ProfRob's answer to If there were undiscovered elements (119 on) in a star's spectral lines, could we tell? in Physics SE begins: I think that would be very difficult indeed. ...
uhoh's user avatar
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1 vote
0 answers
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Raman spectra of peptide

This is my first time measuring Raman spectra of a peptide sample. It is in solid form. I do think I see some Raman peaks but I am not sure how to assign them. I have a peptide sequence through which ...
Mukul Sharma's user avatar
5 votes
1 answer
579 views

Can an electron be excited to a spin state with s ≠ 1/2?

I used to think that all nuclei have fixed intrinsic value of the nuclear spin quantum number, $I$. For example, $\ce{^1H}$ must have a nuclear spin of $\frac{1}{2}$, $\ce{^{14}N}$ must have a nuclear ...
TheLearner's user avatar
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3 votes
3 answers
590 views

How can a 90 degree pulse cause precession perpendicular to the applied field in proton NMR

From my understanding, a proton's magnetic moment in an NMR experiment can undergo precession in only two discrete states: either parallel to the applied magnetic field, or antiparallel to it. ...
John John-man's user avatar
0 votes
1 answer
161 views

Why is this graph of vibration spectroscopy like this?

This graph shows the absorbance of different wavenumbers of infrared radiation causing different forms of vibrations of the water molecule. I would like to know why the graph turns out the way it is. ...
lazearoundallday's user avatar
1 vote
0 answers
124 views

how to combine Raman spectrum data with different wavenumber

I have two set of spectrum data, the first record (in wavenumbers) looks like this: ... 967.0511723 968.9374611 970.8224407 972.7061127 974.5884787 976.4695403 ... ...
haidan li's user avatar
0 votes
1 answer
1k views

Normalized absorbance/transmittance definition [closed]

In the absorption spectroscopy we can calculate transmittance $T$ of a given sample by comparing how the intensity of the incident beam $I_{0}$ is decreased with the distance (Lambert-Beer Law). $A = -...
user avatar
-1 votes
2 answers
258 views

Why the electrode that is the electron source on a x-ray tube is called cathode? [closed]

In electrochemistry, the electrode that lose electrons and oxidizes is called anode. Why on an x-ray tube the electrode that lose electrons is called cathode?
Tito Morenno Pontes e Souza's user avatar
0 votes
0 answers
130 views

XANES simulation software/code besides FEFF?

I need to generate the XANES region spectra of the Pt L3 edge of a theoretical Pt6 crystal with adsorbed atoms (such as hydrogen, oxygen, etc). It is to generate theoretical references as described in ...
quantum.tyrant's user avatar
3 votes
2 answers
115 views

A good lab demonstration of this particular optical transform pair?

At about 1:11 the video linked below shows what think is the optical Fourier transform of a sine wave as approximated by a saw blade. https://www.youtube.com/watch?v=jzmqeRp_tmk The set-up appears to ...
daniel's user avatar
  • 984
1 vote
1 answer
161 views

Why does isolated chlorophyl emits red light?

If we observe isolated chlorophyl solution with UV light, chlorophyl is seen as red. Explanation suggests that when a specific atom of chlorophyl absorbs UV light, the atom gets excited and in a short ...
Lasha Bukhnikashvili's user avatar
7 votes
1 answer
354 views

Experimental evidence for anomalous electronic configurations of chromium and copper

Chromium ($\mathrm{3d^5\,4s^1}$) and copper ($\mathrm{3d^{10}\,4s^1}$) are fairly well-known exceptions to the aufbau principle, often attributed to the stability of the half- or fully-filled 3d ...
James's user avatar
  • 115
1 vote
1 answer
252 views

Identifying an alkyl bromide from NMR information

This question appeared on an exam and I translate it into English. In the NMR $\ce{H^1}$ spectrum of a pure substance, with molecular formula $\ce{C4H8Br2}$, the following chemical shifts (in ppm) ...
Mrdoubty's user avatar
6 votes
2 answers
679 views

Why does calcium emit circularly polarized light?

One page 31 of Quantum Metrology, Imaging, and Communication by Simon, Jaeger and Sergienko, the authors state that: ... calcium has two electrons in its outermost, partially filled shell; these ...
User101's user avatar
  • 169
2 votes
1 answer
348 views

Why do electron-withdrawing groups deshield outer ring protons?

I understand that ring protons experience deshielding because the induced magnetic field (outside the ring) has the same direction as the external applied field, but shouldn't electron withdrawing ...
mateis's user avatar
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