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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 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 ...
siete's user avatar
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1 answer
168 views

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 ...
Sam's user avatar
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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 ...
TheLearner's user avatar
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2 votes
2 answers
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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
281 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 ...
Mikkel Rev's user avatar
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1 answer
941 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 $cm.molecule$). ...
mranvick's user avatar
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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 ...
Mikkel Rev's user avatar
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118 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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1 vote
1 answer
160 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) ...
Anton's user avatar
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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 ...
Kevin Su's user avatar
5 votes
1 answer
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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 ...
ImJustKawaii's user avatar
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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 ...
C-Consciousness's user avatar
10 votes
1 answer
828 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^\...
Safdar Faisal's user avatar
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1 answer
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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 ...
Christian's user avatar
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2 answers
3k 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 ...
cheekylittleduck's user avatar
6 votes
1 answer
423 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 $...
Gougni Adam's user avatar
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562 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 ...
Steve's user avatar
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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{...
dogman's user avatar
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7 votes
1 answer
2k 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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2 votes
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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 ...
Safdar Faisal's user avatar
11 votes
0 answers
140 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 ...
Silverwilly's user avatar
1 vote
2 answers
418 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 ...
whatzgood's user avatar
4 votes
1 answer
183 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: ...
hafimu2367's user avatar
1 vote
0 answers
703 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 ...
Estefania Garcia's user avatar
5 votes
0 answers
219 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 ...
Jonathan Fey's user avatar
2 votes
0 answers
51 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?...
Ty Smith's user avatar
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0 answers
27 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 ...
Kantura's user avatar
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3 votes
1 answer
64 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)...
quantum.tyrant's user avatar
14 votes
1 answer
7k 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 ...
Eclipse239's user avatar
1 vote
0 answers
113 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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3 votes
0 answers
131 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)^...
physicsstudent2's user avatar
3 votes
1 answer
1k 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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1 vote
0 answers
87 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 ...
Luna's user avatar
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1 vote
1 answer
280 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 ...
94five's user avatar
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1 vote
0 answers
102 views

Maximum number of Spectral Lines "A better quantum model shows that there will be n^2 transitions"?

I was parsing the following post What is the maximum number of emission lines when the excited electron of a H atom in n = 6 drops to ground state? and came across with the reply from @porphyrin. cite ...
Xavier's user avatar
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3 votes
2 answers
863 views

How does the force constant change when a heavier atom is used in vibrational spectroscopy?

(iii) The fundamental band in the IR spectrum of $\ce{^1H^{127}I}$ is found at $\pu{2308 cm^-1}.$ Calculate the force constant for the bond. Assume the molecule can be treated as a harmonic oscillator....
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2 votes
0 answers
31 views

Confusions regarding oscillator in black body and value of one quantum [closed]

Q 1 By saying oscillator I.e atoms in the wall of black body. Do we mean electron ? Because boundary of any atom is electron right. Q2 My textbook say that quantum is the smallest value of energy that ...
Rider's user avatar
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-1 votes
1 answer
83 views

Does electron emit photon when it moves? [closed]

When the photoelectric effect happens or blackbody radiation happens or when an electron jumps from a ground to an excited state, we say light is emitted by electron. Now, light is made up of photons. ...
Rider's user avatar
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2 votes
0 answers
46 views

Why are Methyl vibr. modes called r modes and methylene vibr. modes called d modes

I am coming from a chemical background and currently work in the field of vibrational spectroscopy. When I talk to fellow physicists or chemists I always encounter the same question. "Why are the ...
Tim's user avatar
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0 votes
1 answer
136 views

How does an electron identify whether to absorb a photon of a certain wavelength or not in absorption spectrum? [closed]

How would an electron identify the specific photons of a certain wavelength which are to be absorbed in a Hydrogen atom while creating an absorption spectrum? Well, I was thinking of it like this- Way-...
Habib's user avatar
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0 answers
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What type of spectroscopy can display several vibrational energy levels around the electronic transition?

My question is illustrated as the figure. As far as I know, due to the Franck-Condon principle, the absorption spectrum is related to the ground state to the excited state with the same geometry. Here ...
kote2021's user avatar
2 votes
0 answers
79 views

E1 selection rules for transitions between two Σ states

For E1 selection rules (embodied in the electronic transition moment), to have an allowed transition the direct product of irreducible representations (IRs) must contain the totally symmetric IR. So, ...
sarah bnm's user avatar
1 vote
0 answers
47 views

electronic transition for polyenic molecules

I am having troubles with polyenes states symmetry. I found an exercise on the pentadien, where they ask us to analyze the symmetry of the singlet excited states corresponding to: State S1: π+ →π+ ...
sarah bnm's user avatar
1 vote
0 answers
49 views

How to think about absorption and emission rates and intensity for stimulated emission?

I learned Fermi's Golden Rule applied to absorption and stimulated emission and encountered the following question: Since absorption and emission rates are the same for stimulated emission, why can't ...
ferris's user avatar
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1 vote
0 answers
70 views

How to compute Franck-Condon Factors for spin-orbit states?

I am computing Franck-Condon Factors between the neutral ground state and cationic states to simulate the photoelectron spectra (using Gaussian 16, freq=FCHT). The target cationic state is a pi state ...
Soumitra Manna's user avatar
1 vote
0 answers
32 views

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\...
TheLearner's user avatar
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4 votes
3 answers
228 views

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. ...
rdx's user avatar
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3 votes
1 answer
52 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 ...
S R Maiti's user avatar
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4 votes
1 answer
134 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 ...
Aniruddha Deb's user avatar

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