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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3
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0answers
45 views

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 ...
9
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1answer
321 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^\...
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0answers
64 views

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 ...
3
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2answers
108 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 ...
6
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1answer
139 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 $...
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71 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 ...
3
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0answers
38 views

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{...
5
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1answer
184 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 $$\...
2
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0answers
25 views

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 ...
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81 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 ...
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2answers
161 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 ...
4
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1answer
29 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: ...
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37 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 ...
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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 ...
2
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0answers
44 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?...
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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 ...
3
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1answer
40 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)...
15
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1answer
3k 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 ...
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0answers
30 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, ...
3
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41 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)^...
3
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1answer
162 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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39 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 ...
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1answer
60 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 ...
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Will water interfere with an in-situ XAS measurement of the Pt L3 edge during OER on a water electrolysis cell?

I am trying to design a cell for an in-situ experiment. As much as possible, I was hoping to be able to do it on a PEM MEA rather than on a half cell immersed on an electrolyte. I am thinking that ...
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39 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 ...
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1answer
58 views

I am confused with intensity of spectral lines …? [closed]

Example : FOR BALMER SERIES . HOW ? For (n2 to n1) : (2 to 1) > (3to1) > (4to 1) > (5 to 1) .....so on ......? please help me , I am unable to get that how the intensity of spectral lines ...
3
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2answers
53 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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0answers
24 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 ...
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1answer
41 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. ...
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30 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 ...
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1answer
85 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-...
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0answers
27 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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33 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 ...
2
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0answers
37 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, ...
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0answers
43 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+ ...
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0answers
38 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 ...
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0answers
32 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 ...
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0answers
23 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\...
4
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3answers
136 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. ...
3
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1answer
36 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 ...
2
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1answer
62 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 ...
4
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0answers
48 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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0answers
105 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 ...
9
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1answer
220 views

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 ...
1
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1answer
62 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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0answers
74 views

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 ...
0
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0answers
24 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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0answers
26 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 ...
0
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1answer
39 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 ...
3
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0answers
150 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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