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 [tag:nmr-spectroscopy] or [tag:ir-spectroscopy]) are not available.

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3
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1answer
58 views

Difference between relaxation and resonance leading to an absorption spectral feature?

I need help understanding the physics behind this insightful comment below the question Does water really have strong EM absorption at 3 kHz in solid and 2 GHz in liquid? Why the huge shift?: ...
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0answers
30 views

Determine the velocity of the O fragment after the dissociation

A $\ce{SO3}$ molecule is radiated with light with a wavelength of $\pu{193 nm}$, which results in photodissociation. $\ce{SO3} + \text{photon}(\lambda=\pu{193nm})\ce{-> SO2 + O}$ It is ...
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19 views

How can I know the composition of a gas pocket entrapped in a plastic sheet? [on hold]

I have a 1 mm thick plastic sheet, the plastic is not opaque. Some gas pockets, I would say some bubbles, are inside the sheet; the size of the bubbles is about 1 mm. What methods are available to ...
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43 views

Does something like a fluorescent foil or a fluorescent film exist?

During my experiments I want the emitted laser beams to come back with a different wavelength than the original wavelength using a fluorescent foil or fluorescent film. The laser I'm currently using ...
3
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1answer
36 views

How appropriate/adaptable is HPLC for in situ sample analysis on Titan?

I have a limited background in chemistry (nothing beyond general Chem 2), so I am asking for help with a group project. We have two chemists on our team, but communication is limited at the time and I ...
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2answers
52 views

What does Brightness/ intensity of spectral lines depend on?

My book states that it depends upon "The number of photons of same frequency or wavelength ABSORBED or EMITTED" From what I understood, if many hydrogen atoms within the discharge tube EMIT the same ...
4
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1answer
87 views

Why are there only 6 series (Lymen, Balmer, Paschen, Bracket, Pfund and H.Davy) in the hydrogen atomic spectrum? Why can't there be more? [closed]

The Balmer series, for example, is formed when the electron jumps from $n_2 = 3, 4, 5, \ldots, ∞$ to $n_1 = 2.$ The Humphry Davy series (The last series is formed when electron jumps from $n_2 = 7, 8,...
5
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1answer
52 views

What drives vibrational cooling in an excited stated?

As we excite a molecule from its ground state, $S_{0,v=0}$, to some excited state in a higher vibrational state, i.e. $S_{1,v'=3}$, what drives vibrational cooling within that excited state manifold (...
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1answer
21 views

Soluble compounds to absorb radio-frequency electromagnetic radiation

Are there any soluble compounds capable of absorbing radio-frequency or long microwave radio-frequency electromagnetic radiation? I have noted that metals are often used to absorb these signals, but ...
2
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1answer
79 views

Quantify the effectiveness of baseline correction in Raman spectra

I've produced several thousand Raman spectra using hyperspectral imaging techniques. These suffer from significant fluorescent interference which produces a curved, sloped baseline. Using Matlab, I ...
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0answers
19 views

Image formation in LEEM

currently I'm studying for my master's examination in physical chemistry. The topic will be surfaces and catalysis. To prepare myself I'm reading "Surface Science - An introduction" by Oura. ...
6
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2answers
265 views

Tabulated absorption spectra of greenhouse gases?

Are there any free sources of tabulated absorption spectra of greenhouse gases from UV/Vis to far infrared (say 70 micrometers)? This link shows the net absorption over the whole atmosphere (at least ...
3
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2answers
125 views

Why should AAS use element lamps?

AAS (Atomic Absorption Spectroscopy) is a quantitative analytical technique used to measure very small concentrations of ions in substances. The main idea is that the sample is atomised in a flame and ...
8
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3answers
199 views

Why not use all the colours in colorimetry?

Colorimetry (and it's cousin visible-UV spectroscopy) is a form of chemical analysis that works by sending visible light of one wavelength through the sample. It then analyses how much of the light ...
2
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0answers
29 views

Nice textbook illustration of microwave spectrum for a nearly free internal rotation?

Is it possible to find a nice textbookish example of experimental data for an internal rotation of a molecule, in which the rotation is nearly free? For example, 1-butene is supposed to have a nearly ...
5
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2answers
200 views

Proton NMR chemical shift of water peak in different solvents

Why does the water peak appear at different chemical shift values (ppm) in different solvents in proton NMR spectra? For example, the water peak in DMSO-d6 appears at nearly 3.33 ppm, but the same ...
3
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1answer
168 views

Can anyone help me with this question on vibrational modes of free base porphyrin (C20H14N4)?

4 a. The structure of free-base porphyrin $(\ce{H2P}$, chemical formula: $\ce{C20H14N4})$ is shown below. Given that this molecule belongs to the $D_\mathrm{2h}$ point group (character table given ...
14
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1answer
1k views

Using a gas stove instead of Bunsen burner for a flame test?

In all chemistry labs we use the Bunsen burner. What's the difference between it and a good old gas stove used in home? Can the stove also be used to get positive flame tests for some cations (like $\...
2
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1answer
35 views

What interesting things can be seen in spectra between 400-700nm?

The visible spectrum (400-700nm) tends to give a very blurry spectral picture, as it is not a wide band relative to the typical peak width of features you can find there. Further, the vibrational ...
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0answers
21 views

Is there a simpler way to detect alcohol in a blood sample using IR spectroscopy?

I have seen all sorts of ways to detect alcohol using NIRS (Near InfraRed Spectrscopy) or FTIR, but they are all quite complicated in that they are using and analyzing a very wide spectrum. In ...
4
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0answers
44 views

Software for computations of rovibrational states' energies and corresponding spectroscopic constants in diatomic molecules

I need to compute rovibrational energy levels and also the spectroscopic constants, especially $\omega_e$ to compare my results with other papers. So far I've tried LEVEL16, which seems very ...
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1answer
37 views

Binding energy question [closed]

The electrons in the 1s orbital of chlorine have a binding energy of 273 MJ/mol, but the 1s electrons in sulfur have a binding energy of 239 MJ/mol. Why is this?
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0answers
42 views

Free induction decay in NMR (as stated in Pavia)

There is a statement in a very popular textbook of spectroscopy by Pavia (Chapter 3, Intro. to Spectroscopy), it says "The observed FID is actually an interference signal between the radiofrequency ...
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0answers
20 views

Would two different Plaster of Paris samples have different chemical signatures?

Weird question, but... would a spectroscopic analysis of a plaster of Paris sample reveal a chemical identifier that could be used to compare that sample against another. I want to be able to say ...
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0answers
44 views

Why ¹H–¹⁴N coupling is not observed in ¹H NMR

Since the nuclear spin value of $\ce{^{14}N}$ is $I = 1$, we should expect a coupling between $\ce{^1H}$ and $\ce{^{14}N}$. Hence, the proton peak in a primary amine $(\ce{-NH2})$ should split in a ...
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0answers
33 views

How to obtain spectroscopic constants Omega_e, Alpha_e, B_e, D_e and D_0 from centrifugal constants?

I need to compute a spectroscopic constants of $N_2^+$ states and I would like to do it using LEVEL16 software, due to its high interpolation flexibility. But it seems, that LEVEL16 can only compute ...
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2answers
53 views

Spectroscopic constants - explanation

I'm a beginner in spectroscopy and I have troubles understanding papers describing values of spectroscopic constants. This paper, for example, describes constants $T_e, R_e, \omega_e, \omega_ex_e, B_e,...
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1answer
35 views

Interaction of the oscillating magnetic field of electromagnetic radiation with a molecule or atom

Whenever we read rotational, vibrational and electronic spectroscopy, we find details on the interaction of the electric dipole moment of the molecule with the oscillating electric field of ...
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0answers
41 views

Why does molecular oxygen absorb in the IR range?

I am studying spectroscopy and know that $\ce{CH4}$ and $\ce{CO2}$ are known as greenhouse gases because they are IR active. This is because they have asymmetric stretch or bend vibrational modes ...
2
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1answer
37 views

Can amide bonds fragment in ESI-MS?

Electrospray Ionization Mass Spectrometry(ESI-MS) is a technique in mass spectrometry to get an idea about molecular ion peak. In the ESI-MS spectra of an amide compound, I observed that the molecular ...
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0answers
29 views

How to recreate bioluminescence in fireflies in a lab?

I have several mg/mL of D-luciferin, luciferase (firefly), ATP solution (25 mmol) and MgSO4 (for the mg2+ ions). The experiment has to be done in cuvettes of 2,5 mL (if I get any results, it will be ...
7
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1answer
96 views

What could cause a peak to split into 2 resonances as temperature increases in NMR spectroscopy

I understand that some peaks may coalesce upon an increase in temperature due to an increase in free rotation, this does occur with some peaks in my data. Why might you see a peak split into two other ...
7
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1answer
59 views

How to determine the number of water ligands attached to Pd in palladium chloride aquacomplex PdClₓ · yH₂O?

Normally this can be achieved using UV-vis: there is a strong absorbance around wavelength 220 nm which varies based on the number of ligands. If the palladium concentration is too high, the solution ...
0
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1answer
372 views

What is the maximum number of emission lines when the excited electron of a H atom in n = 6 drops to ground state?

When an electron in a higher energy state jumps to a lower energy state in Bohr’s model of hydrogen atom, it emits a photon which has energy equal to the difference in the energy between the final and ...
4
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0answers
55 views

Internal standard with low T1 for NMR quantification of ammonia

I am trying to quantify low levels of ammonia with NMR. The good news is that ammonia has a very low T1 (<0.5) which shortens d1 a lot. However, I cannot find any internal standard with a T1 that ...
0
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1answer
68 views

Spin-forbidden transition iof bromine

In one of the lectures of my spectroscopy course, the professor claimed that there is a strong absorption band in the UV/Vis spectrum of bromine, associated with a singlet-state to triplet-state ...
2
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0answers
20 views

why do cone cells have broad responsivity spectra peaks?

My understanding of vision is that, although the cone cells in our eyes can detect three colors, there is enough overlap in the responsivity spectra (as shown here: https://en.wikipedia.org/wiki/...
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1answer
26 views

Absorbance maxima of polyenes [closed]

Can anyone tell me how to approach this question from USNCO 2013?
2
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0answers
31 views

How do we determine the proportions of hydrogen to helium (to other elements) that make up the Sun given the absorption spectra?

I am reading about the composition of the Sun and how it is made up of mostly hydrogen (~90%) and helium (>10%) and other elements with much smaller quantities. The explains that different elements ...
8
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2answers
94 views

Flame Test Spectrograms Not Lining Up With Reality

In my AS Level chemistry class we had tried some DIY spectroscopy of flame tests with the aim of identifying anions in certain salts. We got as far as building the spectrometer inspired by Paper Craft ...
12
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2answers
360 views

Relationship between the symmetry number of a molecule as used in rotational spectroscopy and point group

While doing a problem set I noticed that the symmetry number of a molecule turns out (usually) to be half the number of symmetry elements that the point group the molecule belongs to. When I say ...
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1answer
119 views

Why the chemical shift value of a proton be negative in proton NMR spectroscopy where TMS is used as standard reference?

If there's any possibility of chemical shift value of a proton be negative.And if yes...why..when I am using TMS as a standard reference.
3
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2answers
122 views

Why doesn't the current stop in neon lamps when all the atoms have been ionized? [closed]

My personal experience (which could be wrong) tells me neon lamps can theoretically run on forever or at least a very long time. If current is the flow of charge why doesn't it stop once all the atoms ...
4
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3answers
127 views

Heisenberg uncertainty principle and lifetime of the excited state

A key relation in optical spectroscopy also used to derive natural bandwidth is: $\Delta E \Delta t=ℏ$ $\Delta E$ is the energy uncertainty of a state, $\Delta t$ should be the uncertainty of the ...
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1answer
32 views

How to measure UV index? [closed]

I am a high school student so please apologise if I say something very dumb or irrelevant. I am conducting an experiment in which I want to find UV index at different points. Such as under shade, ...
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0answers
52 views

Is it true that “Voigt Circuit” would be able to be fitted to various electrochemical impedance spectra?

"Voigt Circuit" which is a series combination of Voigt elements (i.e. parallel RC's), is commonly used for Kramers-Kronig relations checking; and as I imagine it is generally believed to be able to be ...
2
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1answer
82 views

Formulas for the number of spectral lines

While reading through Narendra Avasthi's Problems in Physical Chemistry, I came across two formulas on p. 64 (Scanned page): When electrons de-excite from higher energy level ($n_2$) to lower ...
3
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1answer
178 views

Raman transition and IR transition

In a character table one can find the reducible representation of vibration of a molecule. In such a table we also see things like $xy,z,x...$. If this corresponds with an irrep we say that IR ...
0
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1answer
27 views

Potential energy curve for dissociation of cation of carbon dioxide

Can anyone suggest me some literature where I can find the potential energy curve or the electronic states for singly ionized $\ce{CO2}$ ($\ce{CO2+}$) dissociating into singly charged oxygen ($\ce{O+}$...
9
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2answers
71 views

High content of potassium reported by spectrometer in silverware items

We tried to analyze a few silver items (800/1000 fineness) using a hand-held ED-XRF spectrometer, which is normally used for analyzing industrial alloys etc. The operating element range of the device ...