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 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 ...
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Calculating rotational constant

The rotational constant B for NO is 1.67 cm-1. Calculate the energy difference (in Joules) between the levels J = 2 and J = 3. (4 marks) $$E_{J=2} = h B J (J + 1)$$ $$E_{J=2} = \pu{6.63E-34} \cdot 1....
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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 ...
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-3 votes
1 answer
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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 ...
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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
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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 ...
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1 vote
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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 ...
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1 vote
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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 ...
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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 ...
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1 vote
0 answers
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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 $\ce{(Fe^2+)}$ ...
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2 votes
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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 ...
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6 votes
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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 ...
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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 ...
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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 ...
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1 answer
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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_\...
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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 ...
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3 votes
1 answer
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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 ...
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2 votes
1 answer
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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 ...
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-1 votes
1 answer
310 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 ...
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1 answer
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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 ...
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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 ...
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3 votes
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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. ...
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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 ...
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5 votes
1 answer
542 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 ...
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3 votes
3 answers
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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. ...
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1 answer
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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. ...
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1 vote
0 answers
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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 ... ...
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0 votes
1 answer
145 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 = -...
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-1 votes
2 answers
82 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?
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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 ...
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3 votes
2 answers
105 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 ...
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1 vote
1 answer
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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 ...
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8 votes
1 answer
261 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 ...
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1 answer
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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) ...
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5 votes
2 answers
569 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 ...
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1 vote
1 answer
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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 ...
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Why are HOMO and LUMO energies invariant under spin-flip?

Atomic theory says singlet and triplet energies for the same orbital differ because of exchange interaction. However, molecular orbital (MO) theory describes the energy between the HOMO (highest ...
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1 answer
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How to identify an error in cut off filter (optical) usage when running spectrophotometry?

In spectrophotometry, often a cut off optical filter is used. With reference to a long-pass filter, which rejects any wavelengths outside a predetermined interval: low transmission in short ...
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How do I quantify a mix of SiO2 (amorphous), silicon (amorphous, polycrystal), graphite (dust) in a solid sample?

I collected solid samples from a plugged tube-side of a heat exchanger. These deposits include compounds such as hexachlorodisilane, hexachlorodisiloxane, pentachlorodisilane, graphite dust and ...
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2 votes
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Is there any magnetic resonance spectroscopy that based on orbital angular momentum?

The different momenta of electron and nucleus are described by different quantum numbers. (a) l and m$_l$ describe the orbital angular momentum and quantization on its component along an arbitrary ...
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2 votes
2 answers
135 views

Elucidating an unknown compound using 1H- and 13C-NMR spectral data [closed]

I am currently struggling with the following NMR spectrum for this compound: I know for sure that we should multiply the integrals of the hydrogen atoms by four, and that the compound contains at ...
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1 vote
1 answer
62 views

Molybdenum assay (phosphorus vs inorganic phosphate)?

Recently, I have been getting blood tests done for phosphorus. I see some laboratories report phosphorus and others report inorganic phosphate. The normal range for phosphorus seems to be about 0.1 ...
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0 votes
0 answers
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Spectroscopy of phosphite

These images were taken from IChO 2002 prep problems. May I please know why there are 7 peaks for C-H? This indicates that there are 6 hydrogens the H in the C-H is coupled too, but I can only find 5 (...
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1 answer
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Conversion from Spectral Line Intensity to Absorbance (HITRAN)

The HITRAN spectral database gives access to the spectral absorption lines of various gaseous species. These lines are given as $S$ values in units of $cm^{-1}/(molecule·cm^{-2})$ (or $cm.molecule$). ...
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General cleaning solution for clinical chemistry applications

I want to reuse some plastic and glass items that I am using to do colorimetric concentration analysis of serum and urine. There are some enzymatic assays, mineral assays and so on. I have been trying ...
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5 votes
0 answers
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Meaning of $^2[\,1/2]$ terms in atomic spectroscopy

I was trying to analyze some atomic emission spectroscopy data and I encountered unfamiliar notation of the terms for me. Commonly, the electronic states of the atoms can be described by quantum ...
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1 vote
1 answer
92 views

Vibrations of metal complexes (polyatomic molecules)

I am reading about vibrational spectroscopy of polyatomic molecules and specifically about metal complexes. What I don't understand is what happens on the vibrational modes of the ligand (e.g. water) ...
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Spectroscopic constants weye and weze

I am using Morse potential to calculate the spectroscopic constants of a diatomic molecule. So far I was able to calculate $R_e$, $\omega_e$, $\omega_ex_e$, $B_e$ but wasn't able to calculate $\...
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1 answer
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Can chemical composition be determined from elemental composition?

I have the energy dispersive X-ray spectroscopy results from a sample of salt that I produced by collecting and processing ocean water by filtering, boiling, evaporating, and additional steps to try ...
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4 votes
1 answer
463 views

Can resonance structures account for NMR spectroscopy chemical shifts?

I am unable to understand why the alpha carbon to the carbonyl group is of lower chemical shift compared to the beta carbon based on the effects of electronegativity and hybridisation. Since if ...
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