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 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 ...
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2answers
73 views

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

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-...
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Question about spectroscopy problem [closed]

How to show that CnHn(hydrocarbon) has just a single IR active C-H stretching mode? I am not sure the statement below is correct or not. In order for a vibrational mode to absorb infrared light, it ...
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25 views

Why aren't all the fluorescence transitions the same wavelength?

If all the excited molecules at higher S1 vibrational states rapidly relax to the lowest S1 vibrational state, why do the fluorescence transitions from v' = 1, v' = 2, v' = 3, and other states to v&...
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1H NMR Broad peaks for Ethyl Chloride in benzene d6

Why do we see very broad proton NMR lines for a sample of ethyl chloride in benzene-d6 saturated with oxygen?
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1answer
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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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30 views

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 ...
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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, ...
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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+ ...
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2answers
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Difference between an absorbance, emission, and excitation spectrum for uv-visible spectroscopy

The exam paper answer is 500, because we need the wavelength of "maximum absorbance." But this graph shows two curves, and the absorbance curve is omitted. But what is the difference between an ...
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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 ...
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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 ...
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3answers
123 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. ...
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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\...
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1answer
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Why No Change in Polarizability in Asymmetric Stretch?

In order for a molecule to be Raman active, there must be a change in the polarizability, meaning that there must be change in the size, shape or orientation of the electron cloud that surrounds the ...
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1answer
27 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 ...
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1answer
844 views

How are polarizabilities measured experimentally?

Most common spectroscopies that produce either a full spectrum, a tensor, or a scalar value have a specific instrument associated with them that is relatively self-contained and not custom. For ...
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1answer
50 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 ...
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42 views

What is dispersed fluorescence spectroscopy?

There's quite a few papers mentioning the use of dispersed fluorescence spectroscopy (such as this, or this), but I cannot find any explanation to what dispersed fluorescence spectroscopy is. What ...
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How to determine which levels correspond to each other in LS coupling and jj-coupling?

In the LS coupling scheme, L, S and J are good quantum numbers; whereas in jj-coupling scheme, j1,j2 and J are good quantum numbers. I have learnt how to get the term symbols for LS coupling, and for ...
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1answer
302 views

Mechanistic Explanation of Circular Dichroism

I'm wondering if someone can give me a physically motivated reason for why chiral molecules interact with left and right circularly polarized light (LCP) (RCP) differently. Particularly, a quantum ...
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0answers
45 views

How to determine the source of sub-nm periodic error in NIR spectra

I've run into an issue collecting measurements on deionized water in the $1050-\pu{1200 nm}$ range. To determine the sensitivity of my spectrophotometer in this range, I've acquired measurements on ...
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90 views

How to draw molecular orbital diagrams for protonated/deprotonated methyl red?

Give a molecular structure-based explanation for the differences in the UV-Vis spectra in I and II. Use detailed MO schemes for A and B for illustration. (12 marks) Does the double bond of N=N, C=O ...
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1answer
53 views

Does using same calibration curve for chemical analysis introduce correlation in sample error/uncertainty values?

I am using a hypothetical case to explain my question Let us consider a chemical analysis method A (using a certain instrument), which is used to quantify the value of a particular species b. ...
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Negative DBE/Degree of Hydrogen Deficiency?

I tried calculating the Index of Hydrogen Deficiency for C6H15SiCl, and I get negative one. I get this value by subtracting the number of chlorine and hydrogen atoms from that of the carbon atoms, and ...
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22 views

Why hydrogen gas tube produce hydrogen atomic spectrum

To measure the atomic hydrogen spectrum people often uses hydrogen gas tubes as light source. Since the gas in the tube is the molecule $H_2$ , why we obtain the spectrum of atomic hydrogen? My guess ...
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25 views

vacuum pack of a substance/substrates

What equipment can I put a substance or substrate under vacuum pack? After buying this SERS silver substrates (which can rapidly decay in air). I need to immediately put them in vacuum packaging or ...
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1answer
37 views

Will Raman photon counts/Spectral resolution increase if laser beam becomes parallel? [closed]

Most Raman spectrometer has the laser converging into focus with the sample at center like this. Usually how many millions of H2O atoms will be covered by one spot size? What will happen if the laser ...
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2answers
1k 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 ...
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82 views

Why do molecules showing a pure rotational spectra require a permanent dipole?

I understand that pure rotational spectra only exist for molecules which have a permanent dipole moment. The common explanation is "so that they can interact with the E-field of the incoming ...
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0answers
30 views

Finding wavelength of the centre of Stokes Ro-vibrational spectrum

I have the following rovibrational Raman spectrum for $N_2$: and I am trying to calculate the "wavelength where the centre of the Stokes ro-vibrational spectrum would be observed" if the $...
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0answers
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Can you do SERS without a Raman microscope?

Surface-enhanced Raman spectroscopy or surface-enhanced Raman scattering (SERS) is a surface-sensitive technique that enhances Raman scattering by molecules adsorbed on rough metal surfaces or by ...
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What plastic is this? (Raman scan)

I can't recognize the Raman spectrum of this plastic. It's not in the common plastics raman spectrum. It is plastic adaptor for connecting sediment filters. Anyone got idea or recognize what kind of ...
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4answers
1k views

Is it safe to look at a mercury gas discharge tube? [closed]

As part of a chemistry course, I recently observed a demonstration in which the instructor electrified a mercury gas discharge tube (the tube looked something like this image). The glow from the tube ...
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0answers
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1,5-Pentanediol MS

I'm having troubles assigning the signals m/z = 41 and 56 of the compound 1,5 pentanediol. I tried the basic fragmentations (McLafferty, loss of OH radical, etc.) but I can't figure the structure of ...
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22 views

How can I cluster infrared spectra?

This is sorta a cross-post from my post in StackOverflow. Although, rather than seeking help with the code I'm here asking for help with a chemical/statistical problem associated with the code. I'm ...
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2answers
61 views

Raman signal of black matte object

This is the raman spectrum of the black cap: I was expecting it to be Polypropylene but the peaks didn't match in wave numbers. Anyone got idea what kind of plastic has that peaks on the side of 1500?...
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1answer
11k 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 ...
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Alternating heavy metal materials analysis

If someone had a material that was made of alternating heavy metals (ABAB) and each layer was 1 micrometer thick, would an electron beam be able to displace electrons in the lower layers? If these ...
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Analyzing alternating metals in a polymer matrix with 1 micrometer depth and only 10% metal

This is a theoretical question that I am struggling to get started on for a seminar discussion. If you were attempting to design an instrument with all the basic components (source, analyzer, detector,...
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1answer
39 views

Does increasing the number of interferometers increase signal in FT-IR?

I'm trying to understand why most modern FT-IRs have three interferometers. Does this improve the signal in someway or does it have another effect?
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1answer
35 views

Is the Hydrogen spectrum only an emission spectrum?

In a statement question it was stated that hydrogen spectrum is an emission spectrum and the scheme considered it to be ture. But my argument is that it can be both emission and abosorption spectrum. ...
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0answers
29 views

How would you examine samples of rocks using a handheld spectrometer?

My friend has an old spectrometer set that his father used to own and we are trying to figure out how to use it. Asking his father about it is not an option unfortunately. The box contains a handheld ...
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2answers
72 views

Implications of the excitation spectra

The fluorescence excitation spectra show the change in fluorescence intensity as a function of the wavelength of the excitation light. I'm interested in the certain physical implications of the above. ...
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33 views

Point group specific definition

Does the term only refer to molecules that have the same symmetry elements or exactly the same symmetry operations. Online I see that its the same symmetry operation however my professor's slides show ...
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17 views

For Fe2O3 what could an XPS peak at 711.9 eV mean

For an XPS spectra of Fe2O3 film on graphite there are peaks at Fe 2p1/2 = 724.2 eV and Fe2p3/2 = 709 eV but there is another peak at 711.9 eV that I can't identify. Any ideas on what this might be ...
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What are the advantages of using ellipsometry over AFM to determine film thickness?

I am trying to understand why one would chose one over the other and I am struggling to understand this since both are non destructive. I know AFM can only go at 5 nm but other than that I don't see ...
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1answer
67 views

Why would Auger electron detection have potential for higher spatial resolution than EDX

I understand that Auger electrons are emitted when an electron falls from a higher energy level to a open inner shell and EDX uses electrons that fall from outer shells when an inner shell is kicked ...
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1answer
151 views

Plotting the data using Beer-Lambert law [closed]

For the spectroscopy lab we had a stock dye ($\pu{1.00E-4 M}$ Erioglaucine Blue) that we had to dilute. We had to dilute $\pu{1 mL},$ $\pu{3 mL},$ $\pu{5 mL},$ $\pu{8 mL},$ and $\pu{10 mL}$ in $\pu{...
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1answer
28 views

CNT Raman ratio of G band to 2D band?

I believe that the G band (~1600 cm-1) shows the stretching mode of the graphene in a carbon nanotube (e.g. chiral, zigzag, armchair) and the 2D band (~2680 cm-1) shows the number of walls in the CNT. ...

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