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 Raman Activity Require Anisotropic Polarizability?
Normal mode of a molecule needs to involve the change in molecular polarizability (anisotropic polarizability) to be Raman active.
Explanation is provided in Physical Chemistry textbook by Atkins on ...
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Apparent color of nickel(II)chloride and nickel(II)chloride hexahydrate
Why does anhydrous nickel chloride (NiCl2) appear yellow, even though chloride ions are considered weak field ligands, which should result in a smaller ligand field splitting energy and the absorption ...
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What shifts protons on a benzene ring to lower ppm?
Why do these protons appear at 6.9 and 6.93 ppm, at lower ppm value? I assumed it was due to the anisotropic effect, specifically I thought the circulating (pi) electrons induced a magnetic field ...
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What's the reason of curvature in Tanabe-Sugano diagrams?
Analysing Tanabe-Sugano diagrams it's evident that some of the lines are pretty parallels to that of the ground field whilst others are inclinated or have some curvature.
I know what's the effect on ...
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Convergence limit of emission spectra for atoms with multiple electrons
In high school chemistry, students are taught that the convergence limit in the emission spectrum of an element can be used to determine the first ionization energy.
However, what about the second, ...
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Commutating operators of angular momenta
I've studied the formal procedure to pass from the uncoupled basis set of individual angular momenta to the coupled basis set of total angular momenta for polyelectronic atoms.
I start from an ...
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Why don't I get a whole number when determining the vibrational energy level of F2? [closed]
This is a cross post from physics stackexchange. I hope to get more answers here, because I think chemists have more to do with such things.
So I was playing around with some data and formulas and ...
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Doubt on vibronic transitions
When we justify the presence of electronic transitions forbidden by Laporte selection rule, the coupling between electronic and vibrational states help us. Why we say that in this way we are ...
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Are these formulas for the critical value for detection interchangeable?
I am trying to compare equations for calculating the critical value for detection. One is presented by the ISO standards (https://www.sciencedirect.com/science/article/pii/S0969804316306455?via%3Dihub)...
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What the book means for "percentage difference"?
From Atkins-De Paula, Physical Chemistry, Ninth Edition, page 485
Not sure what the books means as "percentage difference".
Btw, this is my attempt
Fundamental vibration, in wavenumber, ...
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Calculating Rotational Temperature from an FTIR Spectrum
I am trying to calculate the rotational temperature of a sample of gas phase HCN from an FTIR spectrum. It's a 10 Torr sample in a 10 cm gas cell, held at room temperature. In theory, I should be able ...
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Software to draw one-dimensional PES including vibrational energy levels
I am trying to represent the difference between the an anharmonic and harmonic treatment of vibrations. The easiest way to do this is to present an example of a harmonic and anharmonic potential ...
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Datasets of Light Absorbance Spectra for Atmospheric Gases
I am currently doing some thermal/aerospace engineering research that involves finding light absorption in different points in Earth's orbit.
What is the best way to find absorbance vs. wavelength ...
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Equipment recommendation for atomic absorption spectroscopy (AAS) testing for mercury, lead, and cadmium
I work in a public health laboratory in a small mining town and we have the chance to buy equipment to test for lead and cadmium in wastewater, and mercury in not just wastewater, but also in blood, ...
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Franck-Condon principle and shift of wavelength
I was revisiting my notes for spectroscopy, and I came across the Franck-Condon-principle. I understand it well, but want to clear some doubts regarding this.
I know that the Franck-Condon-principle ...
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When a 7-membered ring is formed during GC/MS, does the substituent need to start with a carbon?
When looking at the GC/MS for Allylthiobenzene aka allyl phenyl sulphide, two clear peaks are seen at 91 m/z and 65 m/z, most common for 7 membered and 5 membered carbon rings respectively. The ...
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Auxochrome groups and red shift
Wikipedia states that "An auxochrome is known as a compound that produces a batochromic shift, also known as a red shift because it increases the absorption wavelength, thus approaching infrared ...
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Polyatomic molecule vibrational spectra - Molecular dipole expansion in Taylor series
To give some context: I am studying the molecular spectra in the context of an introductory course to atomic and molecular physics. My professor is using the transition rate expression from an initial ...
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How to proceed with iodometric titration to determine caffeine concentration in liquid coffee?
Context
I'm a high school student who decided to investigate the relationship between caffeine concentration and brewing temperature of coffee out of their love for the substance. For my method, I ...
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Does Warburg impedance predict zero DC current in an Electrode/Electroyte interface?
I'm trying to understand how/if the Warburg impedance, Z_w, of an electrode-electrolyte interface dominates the impedance at low frequencies. I cannot understand how this model can predict a DC ...
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How to get continuous spectral data into intensities of channels centered around wavelengths?
Currently, I am looking into using a spectral sensor from SparkFun in order to obtain spectroscopic data to feed into a trained neural network, however this sensor gives intensities based on inputs ...
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How to read 1H-NMR- and IR-spectre (for ibuprofen) [closed]
I have read the answers to related/similar questions. They didn't help.
I have to read a proton-NMR-spectrum and an IR-spectrum of ibuprofen. The structure formula is given to:
I have not been ...
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What does it mean when there is a term in parenthesis in an electronic configuration?
This may be a silly question, but I have not yet found an answer and I don't really know how to word my searches. I have been looking at the NIST Atomic Spectra Database (and also atomic physics ...
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Explaining the low-lying electronic state of NO
The question asks the following:
'The molecule NO has a low-lying electronic state 0.015 eV above the ground electronic state. Explain why this is the case and state the electronic degeneracies of ...
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Deduce the shapes of stretching modes of a tetrahedral molecule
This question is in relation to the [FeCl4]- molecule, which is tetrahedral. I previously deduced, using symmetry analysis, that the vectors corresponding to the bonds of the molecule will be A1+T2, ...
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Why does H2O appear as spikes in IR of air?
In the IR of air shown below, the region for water at 1500 cm-1 is hard to individually assign peaks due to their "spikey" nature. Is there any specific reason for this or does it just ...
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The extinction coefficients of oxymyoglobin and ferryl myoglobin
I want to know what the extinction coefficients of oxymyoglobin and ferryl myoglobin are. I was able to find the one for the oxymyoglobin in this pretty old article (it says that it equals $121 \text{...
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What is the origin of the spin selection rule?
Why is the change in total spin ∆S = 0 during an absorption of a photon, in contrast to the ∆L = ±1, where the photon transfers its angular momentum?
I am aware that spin-orbit coupling breaks this, I ...
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Why does hydrogen bonding cause a broad stretch in IR spectroscopy?
So hydrogen bonding is an intermolecular forces. I'm assuming that the hydrogen bonding strength varies between molecules and some molecules won't undergo hydrogen bonding causing different bond ...
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NH protons not appearing in H NMR spectrum of 3,4-dihydropyrimidone derivative (solvent: CDCl3)
My synthesized compound is 3,4-dihydropyrimidone derivative, which has 2 nitrogen in the ring. The $\ce{NH}$ protons are not appearing in the H NMR spectrum and the solvent used was deuterated ...
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Why is the local coupling constant (vibronic coupling) given in eV?
Should the local coupling constant g not be without a unit, as the Holstein Hamiltonian suggests?
$
H=\underbrace{\sum_{P, Q} h_{P Q}^{(0)} a_P^{\dagger} a_Q}_{\text{Fixed geometry}}+\underbrace{\sum_{...
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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{\...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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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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 ...
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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 ...
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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 ...
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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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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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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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