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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1answer
135 views

How can every atom have unique spectral lines?

Why does every element have unique spectral lines? I have studied that spectral lines help us to identify the properties of an element. This is because after excitation when the excited electron(s) ...
4
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1answer
77 views

How to find the lifetime of sodium atoms in the 3p using information on the spectral line width?

I am trying to find the lifetime of sodium atoms at the 3p state using the relationship between the spectral linewidth and the uncertainty principle: $$ \Delta E \times \Delta t = h / 4\pi $$ The ...
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Is there an anisotropy factor (g factor) for TDDFT Abs and CD calculations?

Experimentally, anisotropy factor is calculated by dividing the CD spectra by the absorbance spectra multiplying by a factor of 32980 (in order to get a nondimensional quantity) Theoretical ...
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15 views

LIF spectrum with laser-coupled levels lines as the strongest

Why, if I excited the OH molecule Q-branch transition, my LIF spectrum (recorded during and after the laser pulse) does not result in only Q line being the most prominent, but also P and R lines with $...
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1answer
54 views

Emission spectra (Be and Mg)

The line says Alkaline metals and their salts impart characteristic colour to an oxidising flame. This is because the heat from the flame excites the outermost orbital electron to higher energy ...
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33 views

Interpretation of Carbon-13 NMR Spectra for Chemically Similar Carbon Atoms

I am analyzing the Carbon-13 NMR data from a reaction I will be modifying. There is not NMR data available for the specific compound I am attempting to synthesize; however, the compound I am ...
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16 views

In UV photoelectron spectroscopy why are filled orbitals seen at a higher binding energy?

I understand that the partially filled Ni intersects the Fermi level as there is a change from filled to unfilled orbitals. But what is the explanation for the lower binding energy of the filled 3d Cu ...
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2answers
119 views

How can the formula of WD-40 remain a trade secret?

Wikipedia says WD-40's formula is a trade secret How can it remain a secret today? Can't mass spectrometers, NMR and other equipment be used to determine the structure of the compounds that go ...
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15 views

Difference in transition lifetimes for near-resonant v/s non-resonant Raman effect

I have read that a virtual state is created when Raman scattering occurs. Since this state is forbidden, the molecule upon absorbing a photon (not enough to take it to the next electronically excited ...
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1answer
42 views

Difference between equations for spectroscopy wavenumbers

What is the difference between these two equations and when is appropriate to use which one? We were told that $F(J)$ in this case is $F(J)= E/h$ for units in frequency And $F(J) = BJ(J+1)$ $\...
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25 views

Rotational spectroscopy application of different equations [duplicate]

So we were given two problems and I don't understand why one was solved one way, and another was solved another way Estimate the bond length of 12C16O (pure rotational spectrum) given J''=3 (15.356 ...
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1answer
35 views

Determine bond length via rotational spectroscopy

Estimate the bond length of 12C16O (pure rotational spectrum) given J''=3 (15.356 cm-1) and J'=9 (38.356) I understand that the first step is the calculate the rotational constant. So to do this I ...
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118 views

Hybrid orbitals, photoionization and time dependence

Wikipedia, in the article on Orbital Hybridisation, states the following: One misconception concerning orbital hybridisation is that it incorrectly predicts the ultraviolet photoelectron spectra of ...
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40 views

Can stimulated Raman processes be strong enough to drive out of equilibrium?

In the (spontaneous) Raman process, incident light $\hbar \omega_1$ scatters and transfers some energy $\hbar \omega$ to a vibrational excitation of molecule or solid. Typically this is a very rare ...
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2answers
70 views

H-NMR with 10H integration?

I have the following two spectra (IR and 1H-NMR) see below. The chemical formula is: C16H16O2 Thus DBE = 9 My approach: From the IR, I can see that there's no broad peak around 2500-3300, thus I ...
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1answer
68 views

Does Mie Scattering occur in Liquid or is Rayleigh scattering?

Rayleigh scattering occurs when the dimensions of the scatter is much smaller than the wavelength of the incident electromagnetic radiation. Mie scattering occurs when the dimensions of the ...
6
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1answer
195 views

Empirical Evidence and Assignment of Orbital Energies (Electron Filling)

I see a lot of questions on electron configurations from students at various levels here. Students mechanically remember how to fill orbitals and sorry to say many teachers do the same. Not a single ...
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1answer
30 views

Size of atomic shells

Is the distance of some $n^{th}$ shell ($n$ $\neq$ outermost shell) from the nucleus of an atom different for different elements? If so, then how much is the difference or how could we calculate it?
2
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1answer
101 views

Spectroscopic Determination of an Equilibrium Constant [closed]

I got values of $\pu{5.0E-4}$, $\pu{2.5E-4}$, and $183$ for the following problems. However, these seem to be inaccurate and I'm not sure what to do. Here is the procedure: Obtain 6 disposable ...
4
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2answers
140 views

Raman Scattered (inelastic) photons rescattering outside of capture area

Imagine that you are focusing the raman laser right at the center of the vial sample with water (or any liquid) using 532nm laser. (from "Photometric Standards for Raman Spectroscopy) For raman 180 ...
4
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2answers
206 views

Determine structure from NMR

So I've come across this lovely spectrum of a compund where only its chemical formula is given with C5H9NO. I have made the pictures of the spectrum available below. obviously there is some pretty ...
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0answers
24 views

UV-Vis absorbtion spectra of a radical cation/anion. Is it different compared to its even counterpart?

I am studying gas-phase Uv-Vis spectra of radical molecules. If one electron is removed/captured from the neutral even electron molecule, what can I expect from the absorption spectra? Will new peaks ...
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35 views

What is the effect of applied magnetic field on absorption spectrum?

Upon application of a weak magnetic field, a line in the microwave absorption spectrum of rigid rotor splits into $3$ lines. The quantum number $(J)$ of the rotational energy level from which the ...
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1answer
211 views

Right Raman Spectrum of Cyclohexane

In this site, https://www.princetoninstruments.com/userfiles/files/assetLibrary/Technical%20posters/Poster-Aberration-Free-Raman-Spectroscopy-with-the-IsoPlane.pdf the raman spectrum of cyclohexane ...
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2answers
46 views

Size of target substance in IR and Raman Spectroscopy

Usually what is the size (in nanometer) of the sample or target substance in IR and Raman Spectroscopy? Which one has largest size of sample it can scan, how many molecules or atoms are involved? If ...
2
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1answer
148 views

Spectra from Dipole Moments [closed]

If there is a change in dipole moments such as absorption spectroscopy, there are infrared absorptions (and/or transmittance) corresponding to them. Is the reason change in dipole moments are in ...
8
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1answer
166 views

Any way to see “cubic-active” vibrational modes in molecules?

For molecular complexes with a moderate amount of symmetry there are usually vibrational modes that are neither infrared nor Raman active. Sometimes these modes transform as some cubic polynomial in x,...
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2answers
171 views

Why does the dipole moment of molecules go from positive to negative? [duplicate]

In physics the dipole moment is said to go from the negative to the positive pole, check for instance https://en.wikipedia.org/wiki/Electric_dipole_moment (Elementary definition). This makes sense ...
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1answer
649 views

Spectrometer vs Spectrometry vs Spectroscopy

How do you differentiate between the three? I read that "Spectrometry deals with the measurement of a specific spectrum. There are four primary types of spectrometers: Mass spectrometry 2. Neutron ...
4
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1answer
90 views

Timescales in Chemical Analysis

Has anyone seen a comparative list of typical run times of the techniques used in analytical chemistry? I am making a list of rough timescales of analytical techniques (for a slide). Assume that the ...
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72 views

Why is absorption spectrum of beta-carotene different from Zeaxanthin?

Here are the molecular structures of beta-carotene and zeaxanthin These molecules only differ in the OH groups and the conjugated backbone length is exactly the same. I read that the absorption ...
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0answers
37 views

What does “orthorhombic” actually mean?

I'm trying to understand what it means for a molecule to have orthorhombic symmetry. According to Di Lauro's "Rotational Structure in Molecular Infrared Spectra," a molecule is orthorhombic if the ...
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29 views

Using MP-AES, can I accurately say I've found a metal concentration on one wavelength and not another?

I've been given the opportunity to use an MP-AES for metal detection. I'm testing traces of metals in plants. The plant matter is digested so I have a liquid solution, I expect there to be a lot of ...
9
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2answers
151 views

Radiofrequency transmitter in an NMR experiment: Is there an involvement of (electromagnetic) radio wave?

A student in Chemistry StackExchange asked the effect of radio waves on matter, which led to an interesting set of arguments by some users. It was pointed out that in a proton nuclear magnetic ...
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35 views

Why is the iron inter-system crossing non-negligible at high temperatures?

Inter-system crossing (ISC) is a radiationless process involving forbidden transitions between singlet and triplet state. These are more common with heavy atom molecules, so I understand that ISC is ...
2
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1answer
60 views

In Flame Emission Spectroscopy, what part of the flame is used to measure the concentration of the analyte?

Flame Emission Spectroscopy is an analytical measuring device that relates the intensity of the emitted light relative to to the concentration of the sample. As I am reading an article about FES, I ...
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3answers
198 views

The concept of normal coordinates of a molecule

Sometime ago I had posted the What is the origin of "normal" in normal coordinates and normal modes? in math & sci history problems. Nobody was sure for the reason for using the word normal there -...
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89 views

How to extract force constants for normal modes from ORCA?

I am following the computational method described in Scientific Reports.[1] Where the authors analyze the contribution of each excited state normal-modes to the shift of the transition energy. For ...
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0answers
39 views

Increase of peak intensity in case of hydrogen bonding

Typical motif in case of hydrogen bonds is charge transfer from electron rich acceptor Y to (usually) anti-bonding X-H σ* orbital. If so, the X-H bonding distance increases, bond weakens, stretching ...
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2answers
221 views

Terminology of atomic spectroscopy: Difference Among Term, States and Level

In A Primer on Quantum Numbers and Spectroscopic Notation Contents, the concept of a term and level is described as a) The level is the set of 2J+1 states with specific values of L, S, and J. ...
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36 views

Could coating silver inside of a cuvette be used for SERS?

I understand that molecules adsorbed to a coinage metal surface experience plasmonic enhanced Raman shifts and I have a spectrometer that I would like to perform SERS measurements with but do not have ...
3
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1answer
127 views

Term symbols for nitrogen: determining J

I'm trying to figure out what terms are possible for nitrogen with the electron configuration $\ce{[He] 2s^2 2p^3}$. There is an old question on StackExchange and the corresponding answer was a great ...
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1answer
74 views

Doubt in a question related to electronic transitions in Bohr's orbits

Question In Bohr series of lines of hydrogen spectrum, the third line from the red end corresponds to which one of the following inner-orbit jumps of the electron for Bohr orbits in an atom of ...
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1answer
94 views

Different shapes of fluorescence spectra in Raman

Note: I haven't owned any of these spectrometers. I'm asking so I can decide whether to buy 532nm or 785nm wavelength raman to probe molecular structure (especially solutions) and I'm concerned about ...
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1answer
391 views

Raman Spectrum of Water

This is the Raman spectrum of water. There is $\pu{1635 cm-1}$ Raman peak corresponding to $\ce{HOH}$ and $\pu{3410 cm-1}$ Raman peak corresponding to $\ce{OH}$. But why is there general nonzero ...
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32 views

Infrared Analysis of a Zeise Salt

The reaction of propene with a stoichiometric mixture of platinum (II) chloride and potassium chloride yields a complex, from which the propene may be recovered by treatment with an aqueous cyanide ...
3
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1answer
131 views

Is there a known relation between the diffusion of a molecule and the diffusion of the reactants?

I have a plasma consisting of elements A and B (which have a similar mass). These elements can react to form molecules AB. $$ \ce{A + B -> AB} $$ Now if my plasma or gas is expanding based on ...
3
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1answer
83 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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35 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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21 views

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

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 ...