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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32 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. ...
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47 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 ... ...
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1answer
47 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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69 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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103 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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1answer
93 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 ...
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1answer
197 views

What knowledge of spectroscopy shows us that Chromium has 3d5 4s1 or Copper has 3d10 4s1? What is the physical phenomena of this matter?

We know that Chromium has 5 electrons in 3d and 1 electron in 4s. Another example, Copper has 3d10 and 4s1. What knowledge of spectroscopy shows us this matter? I mean what is the reason for this ...
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1answer
61 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) ...
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2answers
543 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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1answer
36 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 ...
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The mechanism of discoloration due to changes in the state of CP

I don't know the mechanism of discoloration due to phase change. https://pubs.rsc.org/en/content/articlelanding/2019/cc/c9cc02172h In the above paper, Cu(I) in CP1 (Figure 1 a) has a tetrahedral ...
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35 views

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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1answer
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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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1answer
35 views

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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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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2answers
121 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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1answer
37 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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24 views

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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1answer
65 views

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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28 views

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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80 views

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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1answer
59 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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35 views

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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1answer
279 views

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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1answer
220 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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50 views

Are there any ways of modifying molecules to increase their probability of two photon absorption?

While checking two photon microscopy, the use of high flux femtosecond laser is required for the dual absorption of photons, due to the low probability of these two photons being absorbed. Is there ...
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1answer
346 views

Why is a conformer of hydrogen peroxide rotationally inactive?

Hydrogen peroxide may exist in four different forms depending on the dihedral angle, $d = \angle\,\ce{H-O-O-H}$. The four conformers are: Conformer I with $d = 0^\circ$, Conformer II with $d = 60^\...
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118 views

UV-spectra of benzene

I measured the UV-absorption-spectrum of benzene vapor as well as solved in methanol and cyclohexane. The absorption of the vapor was much stronger than in solution. I also noticed that the peaks get ...
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2answers
253 views

Spectroscopy: What is an instrument response function?

Many papers involving ultrafast spectroscopy measure the instrument response function and model it as a Gaussian, but the sources on any of this are never cited and I have no intuition for what this ...
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1answer
212 views

How does a spectrophotometer measure absorbance based on the intensity of detected light?

We know that $\displaystyle A = -\log\frac{I_t}{I_0}$, where $I_0$ is the intensity of light without a sample absorbing, and $I_t$ with the sample. For determining the absorption $A$, we need both $...
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122 views

Limitations of the simple harmonic oscillator?

I understand that the simple harmonic oscillator can be used to model the behaviour of molecules at low vibrational states. But why does this not work for molecules that are highly vibrationally ...
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42 views

How can I set up and process my excitation-emission matrices properly?

I'm running EEMS on some water samples on a Horiba Fluoromax 4 spectrofluorometer. Method below. $\pu{240-580nm}$ emission, $\pu{5nm}$ interval, $\pu{1nm}$ width. $\pu{240-480nm}$ excitation, $\pu{...
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1answer
410 views

Oscillator Strength and Absorption Intensity in TDDFT

When I run a linear-response time-dependent DFT calculation in my favourite electronic structure program, for each excitation I'm given an oscillator strength, $f_i$, and transition dipole moment $$\...
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29 views

Reason for different chemical shift in chiral solvents for enantiotopic protons

The chemical shift of enantiotopic protons is defined as follows in Spectroscopy/Homotopic, Enantiotopic, Diastereotopic Enantiotopic protons have the same chemical shift in the vast majority of ...
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95 views

Using symmetry and group theory arguments to explain iron(II) in a tetrahedral crystal field

I am trying to figure out how to explain $1s \rightarrow 3d$ spectroscopic transitions for $\ce{Fe^{2+}}$ in $T_\mathrm{d}$ symmetry. These transitions make up the pre-edge region in K edge X-ray ...
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2answers
170 views

NMR spectrum chemical shift confusion

Recently started on NMR spectrum, and I'm slightly confused about chemical shifts and their connection to the resonance frequency and magnetic field. From what I know, the "new" way of doing ...
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1answer
39 views

Does the amplitude of the RF pulse affect the NMR signal?

I know that the NMR signal depends on the static magnetic field strength $ B_0 $ (by Boltzmann equation) and its gyromagnetic factor. While NMR occurs when the RF pulse frequency matches the equation: ...
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57 views

Dilution factor and ICP

I did total digestion on a $\pu{0.05 g}$ sample and had a final volume of $\pu{10 mL}$ once it was digested. I then took $\pu{5 mL}$ of this $\pu{10 mL}$ solution and diluted it to $\pu{10 mL}$ with ...
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115 views

Splitting of atomic orbitals due to Stark effect

I am performing graduate level research on ZEKE Photoelectron Spectroscopy and central to this form of spectroscopy is Rydberg states and the Stark effect. The Stark effect is caused by an electric ...
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47 views

How to generate sulphuric acid vapour to test an analyzer?

We have a UV gas analyzer we want to test to see if it reads gas phase $\ce{H2SO4}$. How can we safely produce less than $\pu{5 ppm}~\ce{H2SO4}$ as a spike test to see if the analyzer sees the spectra?...
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23 views

Prepare solution of salt in ethanol

The test for anions can be done with a platinum wire and a Bunsen flame. My textbook says that it can also be done by preparing a solution of the given salt in water and ethanol and spraying it onto ...
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1answer
42 views

Performing XPS on Pt–Ru/C nanoparticles

From what I understand, to get clear peaks, $\ce{Pt}$ is analyzed at $\ce{Pt}$ 4f; and $\ce{Ru}$ at $\ce{Pt}$ 3d. However, if i'm not mistaken, charge correction is needed. But $\ce{Ru}$ 3d(280/284 eV)...
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1answer
3k views

Why does hydrogen burn with a pale blue flame while its emission spectral lines are red in colour?

I was studying oxidising flames and realized that sodium burns with a bright yellow flame the wavelength of which is around 588 nm. Then I searched for emission spectra of sodium and found that the ...
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38 views

Should Birge–Sponer plots always have a negative gradient?

I have a set of data I would like to use the Birge–Sponer extrapolation with, but the data is the wavenumbers of the bands in the vibrational-electronic spectrum of a diatomic molecule for $v' = 0, 1, ...
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45 views

Origin of the D1 line of sodium

According to the fine structure formula for exact energies (Sommerfield formula) $$E_{jn} = -m_\mathrm{e}c^2\left[1 - \left(1 + \left[\frac{\alpha}{n - j - \frac 1 2 + \sqrt{\left(j + \frac 1 2\right)^...
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1answer
258 views

Comparing the zero point vibrational energies of DCl and HCl

(a) Compare the zero point energy (i.e. $E_0)$ in joules for $\ce{H^{35}Cl}$ and $\ce{D^{35}Cl}$ (assuming both are anharmonic oscillators). (b) Explain the effect this will this have on their ...
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39 views

Can % location of electron on metal or ligand be negative (EPR)?

Given an EPR spectrum of [Co(3-methoxysalen)(py)] : and equations: A(x) = A(iso) + B A(z) = A(iso) - 2B %Co in SOMO = B/B0 where A(x) and A(z) are hyperfine coupling constants measured from the ...
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1answer
77 views

How to make spectra smooth by using gaussian or lorentzian function [closed]

I want to use some origin spectrum to fit to my experimental spectra. However, my experimental spectra is not so smooth because of finite resolution of spectrometer. I used to use 'origin' to make it ...
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14 views

Will water interfere with an in-situ XAS measurement of the Pt L3 edge during OER on a water electrolysis cell?

I am trying to design a cell for an in-situ experiment. As much as possible, I was hoping to be able to do it on a PEM MEA rather than on a half cell immersed on an electrolyte. I am thinking that ...

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