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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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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563 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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570 views

Finding the wavelength of maximum absorption of Tartrazine using Fieser-Kuhn

How would you use Fieser-Kuhn rules to calculate the wavelength of maximum absorption for tartrazine? Fieser-Kuhn rules states that: $\lambda_{max}=114+5M+n(48-1.7n)-16.5\ R_{endo} - 10\ R_{exo}$ ...
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183 views

How to get defect-energy level diagram from PL data

I am reading this article Phys. Chem. Chem. Phys. , 2011, 13, 14902-14905 and seen that the authors have drawn a image of defect level using PL data Can you explain me how this diagram can be drawn ...
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1k views

Tables/database/literature of specific or optical rotation

I'm looking for a comprehensive reference of experimental specific rotation or optical rotation data. It can be a published literature review, a free web database with API access or one that permits ...
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73 views

Solving the Schrödinger equation for a rotating triatomic linear molecule

This source is showing that solving the Schrödinger equation for a triatmoic linear molecule yields the same formula for the rotationaI quantum states $BJ(J+1)$ as for dipoles. For dipoles, the total ...
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143 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 ...
6
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148 views

Vibrational Self-Consistent Field

There are a few things about VSCF that I don't understand: Which coordinates do you work in? If you work in normal mode coordinates, how do you evaluate the effect of the average of one normal mode ...
6
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0answers
435 views

Explaining the photoelecton spectrum of krypton

The photoelectron spectrum of krypton is shown below. (where the x-axis is in electron volts (eV))\ Since both the $3p$ and $3d$ shells are more than half full, based on Hund's rules the lowest-...
6
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1answer
92 views

Beer's law: UV-Vis absorbance values exceeding 2

In classical analytical chemistry, absorbance values in Beer's law can theoretically range from 0 to infinity. As general rule of thumb neither high, nor very low absorbance are used for ...
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53 views

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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166 views

Why is spin-contamination undesirable?

Why is spin-contamination, introduced by e.g. Unrestricted Hartree Fock, undesirable, and to which problems further on can it lead? The only problem I currently see myself is that spin-contamined ...
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136 views

Effects on Stretching Frequencies in Organometallic Complexes

If you added a negative charge to $\ce{Mo(CO)_6}$ how would this effect the $\ce{CO}$ stretching frequency in an IR spectrum? My thoughts are that it would lower the $\ce{CO}$ stretching frequency ...
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154 views

FT-IR background lines

I started doing IR spectroscopy a few months ago and have run into the following problem: Here's the IR background that everyone knows and loves: CO2 peaks in the middle, water lines on either side. ...
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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 measured ...
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58 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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83 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 ...
4
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138 views

Evaluating Franck-Condon factors

Franck-Condon overlap integrals are given by $\langle\psi^e_{v_e}|\psi^g_{v_g}\rangle$, where $\psi^e_{v_e}$ and $\psi^g_{v_g}$ are the vibrational functions for the $v^{th}$ vibrational states of the ...
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21 views

Identifying luminescent transitions for lanthanides

Using the ground-state of Eu(III), how can I identify the possible (number of) luminescent transitions from the $^{5}D_{0}$ excited state? I identified the ground-state term symbol for Eu(III) using ...
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195 views

How to solve the Schrödinger equation of 1D hindered rotor?

I have the following equation: $$-\frac{{{\hbar }^{2}}}{2I{}_{r}}\frac{{{d}^{2}}\psi }{d{{\theta }^{2}}}+V\left( \theta \right)\psi =E\psi, $$ with $$V\left( \theta \right)=a+\sum\limits_{n=1}^{...
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117 views

Is there a physical explanation behind the derivation of spectroscopic term symbols?

In deriving the spectroscopic term symbols, one method seems common among several sources, the clearest presentation for me being located here, a derivation of the term symbols for a $d^2$ ion. So, ...
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92 views

Molecular (infrared) vibrations: General relationship between molecular mechanics force constants and harmonic frequencies (in internal coordinates)?

In molecular mechanics method simple molecules, say symmetrical tri-atomics (H$_2$O), have potential energy surface governed by distances $r_1,r_2$ and angle $a$ like $V (r_1,r_2,a_{121}) = K (r_1 - ...
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2k views

How to calculate spectral overlap integral using spreadsheets?

I need to calculate the spectral overlap integral for the emission spectrum of coumarin 334 and the absorption spectrum for rhodamine, using spreadsheets (MS Excel). Following the theory of ...
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126 views

Relevance and Determination of the reflection symmetry +/- in Spectroscopy?

If there are two electrons located in a shell (which contains two subshells) the molecule can either have a singlet state (if both electron are in the same subshell; because of the Pauli principle) or ...
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100 views

Synthesizing monodisperse PbS quantum dots

For a research project, I am trying to synthesize lead (II) sulfide quantum dots using the method of Li et al.. I am injecting sulfur dissolved in 1-octadecene into a mixture of $\ce{PbO}$, oleic ...
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41 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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32 views

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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27 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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48 views

Mechanism of decomposition of alkali metal halides in flames

A student recently asked an interesting question What happens when KCl is introduced in the Bunsen flame?. This apparently simply question led me to an interesting debate. We all know that emission of ...
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49 views

Enantiomers to diasteroisomers (rotational spectra)

Enantiomers have identical rotational spectrum because their mass distributions are identical. Recently a trick has been introduced in microwave spectroscopy in which a enatiomerically pure gas chiral ...
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59 views

Why does Larmor precession occur in NMR?

Larmor precession is the phenomenon that in NMR the spin (and by default also the magnetic dipole moment) of protons does not line up with the applied magnetic field but rather precesses around this ...
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153 views

Why aren't lasers used as light sources for atomic absorption spectroscopy?

Atomic absorption spectroscopy yields extremely narrow signals. It is difficult to separate white light with sufficient precision using monochromators, and hollow cathode lamps are often used as light ...
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131 views

Spectra of Methylene Blue

Does the spectrum of Methylene Blue change on prolonged exposure to light? I've studied about the photochemical reactions and about energy transfer reactions. Methylene Blue is a triplet sensitizer ...
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297 views

Cheap spectral analysis to analyze water quality

I need some guide about spectrometers I saw a lot of DIY spectrometers to analyze light. Does anyone try to use those DIY spectrometers to analyze water? To detect heavy metals? or a chemical? or ...
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333 views

How are hydrogen atoms formed in hydrogen discharge tube?

I (partially) understand how a breakdown voltage is applied, then the gas is ionized to cations and electrons. Then the electrons will accelerate to the cathode and knock off more electrons from other ...
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98 views

Predicting dissociation energy of diatomic iodine computationally

In one of my classes we used ORCA with three different functionals: BP86, B3LYP, and M06-L, all with the basis set def2-SVP. In addition to calculations we did it experimentally by a Deslandres table ...
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90 views

excitation upon emission from 2 LEDs

I came across a problem: I have 2 LEDs with different emission spectra (blue and green). I have 1 molecule with a known excitation spectrum (channelrhodopsin2 protein). I turn on 1 LED at a time. I ...
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464 views

How to calculate the radius of gyration (Rg) and the molar mass from light scattering data (Rθ and θ/degree)?

I have a homework problem that I don’t have a solution for, so I would like understand how to solve it and to know if my suggested way of solving it is on the right track. The problem is as following: ...
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94 views

Why might the ratio between two Q-band peaks in ZnTPP decrease with increasing temperature?

In ZnTPP (Zinc tetraphenylporphyrin), there are two Q-band emission peaks. When I run steady state emission measurements at different temperatures, the ratio of their respective peak intensities ...
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1k views

Why do electronegative heteroatoms increase C=O stretching frequency (bond strength)

Why does a more electronegative heteroatom (i.e. $\ce{Cl}$ or $\ce{O}$) increase the stretching frequency of a carbonyl? I'd suspect it's that they donate their lone pairs and we end up with a ...
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294 views

Spectral reflectance identification of types of iron rust

Based on the Wikipedia page about rust, there are red and green types of rust that occur on iron. Red rust is the reaction with oxygen and water and the green with chlorine (in oxygen poor ...
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352 views

Assign symmetric and antisymmetric stetches in IR spectroscopy

Typically the antisymmetric stretch in IR spectroscopy is higher than the symmetric stretch for a given functional group. For example for $\ce{NO2}$ the antisymmetric stretch falls at $\sim 1530\ \...
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28 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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32 views

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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223 views

Differences in Novichok agent mass spectra

As we have all heard, in 2018, a series of poisonings with a nerve agent alleged to be of the Novichok series was carried out on British soil. It is claimed that the agent used was A-234. However, a ...
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64 views

How is the ΔL = ±1 selection rule derived?

I understand there are selection rules in spectroscopy and quantum mechanics which governs whether a transition happens or not. For example, in atomic spectroscopy, the total orbital angular momentum ...
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30 views

Why is the transition (0,0,0) -> (1,0,1) observed in a gas phase IR spectrum of CO2?

Let ($v_1$,$v_2$,$v_3$) denote the vibrational state of $CO_2$. Why is the transition $(0,0,0)\rightarrow (1,0,1)$ observed when the trasition $(0,0,0)\rightarrow(1,0,0)$ (asymmetric stretch) is not ...
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21 views

Vibrational modes in BiOCl

These are the vibrational modes in BiOCl. I'm trying to account for the each mode, and where in the spectrum you would find such mode. And I found out that at 1400 cm-1 you have asymmetric stretch of ...
2
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42 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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33 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 ...