Questions tagged [uv-vis-spectroscopy]

For questions that are related to the ultraviolet and visible spectrum of compounds, mostly due to electronic transitions between orbitals.

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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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41 views

Changing of UV-Vis peak absorption after heating Ni(en)2(NO2)2

(c) The trans-isomer of $\ce{Ni(en)2(NO2)2}$ D is red $(λ_\mathrm{max} = \pu{500 nm}).$ It can be heated to give a new trans-isomer E, which is violet $(λ_\mathrm{max} = \pu{560 nm}).$ Assume that, ...
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Nanoparticle Alloys (Gold-Silver) not forming

I have synthesised what I thought were gold-silver alloys at various different compositions. The UV/vis data showed that nanoparticles alloys with a majority of the composition made from gold had one ...
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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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Are there any forbidden collisional electronic transitions?

There are spectroscopy selection rules marking some radiative electronic transitions as forbidden. For example, it is stated that single electron of H atom can not move from S2 to S1, or from P2 to S2 ...
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32 views

tolerable error, CASSCF simulation of UV/Vis spectrum

Please forgive my ignorance of experimental spectroscopy. I am a computational chemist, not an experimental one. My question is: what would be considered a tolerable or reasonable difference between ...
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136 views

Spectral database in the UV-Vis/NIR and IR regime

I'm searching for a bunch of spectra (some tens), preferably with intense bands in the Vis spectrum, to play around with (calculating chromaticity, etc.). They should range from 250 nm to 2500 nm (UV-...
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34 views

How to assign initial and final states of iodine transitions in its spectrum?

In an experiment, I gently heated iodine crystals to create vapors and then observed it absorption spectrum with a spectrometer. The temperatures throughout were moderate (maximum $40^\circ\text{C}$). ...
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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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37 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 ...
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47 views

Why do carbonyl groups lower antibonding orbital energies of conjugated systems?

In the chapter on conjugation in Organic Chemistry by Clayden, Greeves, Warren and Wothers, there's a brief discussion of pigments with conjugated systems that includes the following paragraph (first ...
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34 views

Standard Solutions for UV-Spectrophotometry

Can one use a mixture of compounds when making a standard solution for UV-Spectrophotometry. For instance, one is attempting to find the casein concentration of milk using UV-spec and they have milk ...
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77 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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33 views

How do elemental halogens get their colour?

I learnt that in halogens the colour is due to transfer of electrons from HOMO to LUMO during excitation but I have trouble understanding what that means. Also I don't understand how iodine is ...