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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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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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 ...
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Spectra from Dipole Moments [on hold]

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 ...
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How could one use a colorometer to ascertain the content of a given solution? [closed]

https://www.chemedx.org/blog/use-your-smartphone-absorption-spectrophotometer I saw this blog post recently and got really interested. I can imagine all sorts of future applications for this in my ...
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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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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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154 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 ...
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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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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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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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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 ...
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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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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 ...
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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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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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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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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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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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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 ...
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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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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
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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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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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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 ...
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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 ...
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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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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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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 ...
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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 ...
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1answer
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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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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 ...
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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,...
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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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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 ...
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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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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. ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 $\...
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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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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 ...
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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
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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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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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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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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 ...