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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12
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2answers
6k views

What is an exocyclic double bond?

I have been tasked to find the $\lambda_{\text{max}}$ of 3,4-dimethyl-1,2,3,4,4a,5-hexahydronaphthalene. This was supposed to be fairly easy. I used the base value for homoannular diene ($\pu{253 nm}$...
8
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3answers
476 views

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 ...
7
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1answer
251 views

Notation for excited states

I am reading some papers about quantum chemistry and in one I found a notation for excited states of a molecule that I don't understand at all. In the picture below you can see the potential curves ...
7
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2answers
71 views

Does broader peak mean stronger absorber in UV/VIS?

I want to ask a question about peaks in a UV/VIS spectrum. My lecturer in our introductory course mentioned the following: Two molecules may have the same molar extinction coefficient, but if I ...
6
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2answers
237 views

Visible Light Spectrophotometer Recommendations

I’m looking into purchasing a cheap uv-vis spectrophotometer but am not affiliated with an institution at the moment given the whole COVID 19 situation. Are there any good recommendations for cheap ...
6
votes
1answer
62 views

Why is the graph of fluorescence vs. wavelength continuous?

If the emission of a photon from an excited state to the ground state occurs with a precise energy, then why is it that wavelengths that differ from lambda max have values on a fluorescence vs. ...
5
votes
1answer
103 views

pKa of phenols using UV-Vis spectroscopy

I have done an experiment where I dissolved four different substituted phenols in acidic, basic, and buffer solutions, and recorded the UV-Vis spectra for each. I'm supposed to pick a wavelength where ...
5
votes
1answer
589 views

Why does benzene have 3 π–π* transitions in the UV range, but ethene, butadiene, and hexatriene each have only 1?

Are the π and π* orbitals of benzene much closer together in energy which allows for multiple transitions? Why is this not the case for hexatriene if they both contain the same number of pi bonds?
5
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1answer
1k views

Beer's law with a polychromatic light source

As is well known, Beer’s law (aka the Beer-Lambert law, among others) is predicated on a number of conditions, one of which is that the light source be monochromatic or, as a practical approximation, ...
5
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0answers
51 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 ...
4
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0answers
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, ...
4
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0answers
38 views

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 ...
4
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0answers
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 ...
3
votes
3answers
283 views

De-excitation of a molecule

In our chemistry lecture today on UV/vis-spectroscopy, we discussed the origin of colour in conjugated molecules due to electronic transitions from lower-energy molecular orbitals to higher-energy ...
3
votes
2answers
7k views

Woodward Fieser rules for dienes - non conjugated double bond as exocyclic?

When looking for exocyclic double bonds in a diene, should a double bond not connected to the conjugated system be considered? For example, in this compound, should the marked double bond considered ...
3
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1answer
104 views

Why we should concern with A∞?

To determine the order of one reactant at pseudo concentration of another reactant the plot of $\ln(A_t - A_∞)$ versus $t$ is used. $A_t$ is absorbance of the intermediate at time $t$. $A_∞$ is ...
3
votes
1answer
205 views

Equation for the equilibrium constant for the hydration of carbonyls using UV spectroscopy

I was looking through the literature when I found a paper by Greenzaid et al. [1] which states that the equilibrium constant $K_\mathrm{hyd}$ is: $$K_\mathrm{hyd} = [\text{hydrate}]/[\text{carbonyl}] ...
3
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0answers
64 views

How does Mars rover Curiosity's ChemCam's infrared laser produce a 100,000 K plasma plume (kT = 8.6 eV)?

Mars rover Curiosity's ChemCam uses a pulsed diode-pumped solid-state laser (DPSS) at 1064 nm to excite material on the surfaces of rocks up to 7 meters away, and a large aperture telescope to collect ...
2
votes
1answer
74 views

Different force constant in ground vs excited state in spectroscopy

The force constant of iodine in the first excited state is $k=41.78$ N/m, and in the ground state it is $170$ N/m. I know that the formula for calculating $k$ is: $$ k= (\frac{ΔE_{vib} *2π}{h})^2 µ$$...
2
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1answer
205 views

Why is UV-Vis Spectroscopy not like IR Spectroscopy

UV/Vis Spectroscopy is where electromagnetic radiation in the UV to Visible range is shone at a sample to be analysed. The absorbance of each wavelength is recorded and then plotted (very similar to ...
2
votes
1answer
38 views

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 ...
2
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0answers
65 views

What type of FDA process does a 222nm Kr-Cl excimer UV-C light have to go through [closed]

There are plenty of articles and preliminary research about this type of light being able to kill virus as effectively as 254nm UVC light, but not harmful to human skin and eye. This is wonderful news ...
2
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0answers
34 views

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 ...
2
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0answers
36 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 ...
2
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0answers
148 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-...
1
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2answers
77 views

Why do some molecules show non-symmetric absorption and emission bands?

I'm looking at a molecule of [Ru(bpy)3]2+ in water and the absorption and emission bands are not symmetrical. I want to know why the mirror image rule doesn't apply here. Is this because of the MLCT, ...
1
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2answers
328 views

Reason for usage of Metal chlorides and Platinum or Nichrome wires in flame test

I'm studying about the s-block elements in my course of Inorganic Chemistry and I happened to come across the following text. Electrons may be quite readily excited to a higher energy level, for ...
1
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1answer
52 views

UV Absorption of iodine with some solvent

$I_2$ in solution is typically absorbing around $525 \; nm$ this is why it appear to be magenta, I recently learn that with some solvent : Benzene Toluene $o$-Xylene $p$-Xylene The coordination ...
1
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3answers
181 views

Is a hue indistinguishable from its equivalent frequency of light?

A hue is the color characteristic of a pigment, a particular chemical molecule, when illuminated by sunlight. Of course such a molecule will not emit a single frequency of light, but will emit a ...
1
vote
1answer
45 views

Can I make UV-Vis calibrant in the lab?

I have a Thermo Nanodrop 1000 spectrometer that I have reason to believe is out of calibration. After consulting the manual, it appears as though there is a way to check the calibration of the ...
1
vote
1answer
159 views

Molar absorption coefficient for potassium hydrogen phthalate

I would like to draw a comparison of the sensitivity between several spectrometers. Therefor I measure the absorption of a serial dilution of potassium hydrogen phthalate (KHP). The idea is to compare ...
1
vote
1answer
50 views

Connecting a computer to Genesys 10S Spectrophotometer

Has anybody ever connected a computer to a Thermo Scientific Genesys 10S Spectrophotometer without their (costly!) software? I'd like to pull absorbance data off of it to perform analyses. There are ...
1
vote
1answer
30 views

Chemical equation to represent the hydrogen peroxide scavenging experiment, used to determine antioxidant ability of tea

I am currently investigating the antioxidant ability of tea using hydrogen peroxide scavenging. Basically, I will look at absorbance of the tea samples with and without the addition of hydrogen ...
1
vote
1answer
126 views

Determination of Urea and Hydrogen Peroxide in Cow Milk by ATR-FTIR(Attenuated total reflection-Fourier Transform Infrared Spectroscopy) [closed]

I am doing a research on cow milk adulteration. I am checking Urea and Hydrogen Peroxide content in milk by ATR-FTIR(Attenuated total reflection-Fourier Transform Infrared Spectroscopy). I am using $\...
1
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0answers
36 views

Photoluminescence Spectra of Solids

What information can we gain with the photoluminescence spectra of solids? The bandgap can be determined for example, but are there any other useful properties we can learn? I care about this in the ...
1
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0answers
21 views

CO2 dynamics-vector correlations [closed]

I would like to ask if anyone has any information (schematic diagram)of vector correlations for CO2 molecule. (Is it bending in the excited state with μ in plane? How CO fragment can be ejected after ...
1
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0answers
37 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 $40^\circ\text{C}$). ...
1
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0answers
28 views

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 ...
1
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0answers
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 ...
1
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0answers
76 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 ...
1
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0answers
53 views

Determination of pKa and molar absorptivity coefficient using spectrophotometry [closed]

An indicator BPB (Brophenol Blue) is used and dissolved in solutions of various known $\mathrm{pH}$. Then, the absorbance of each solution at 590 nm was measured and the question asks for molar ...
1
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0answers
35 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 ...
0
votes
1answer
56 views

laser diode problem [closed]

I'm a student studying chemistry, i'm working with diode laser to look at emission spectra for certain complexes. i'm using integrating sphere as my setup, when i use the 405nm diode laser output of 4....
0
votes
1answer
48 views

How to change pH of CuSO4?

I'm currently very desperate to know this. I'm doing an experiment about adsorption/chelation of Cu ions in CuSO4 using banana peels using the UV-Visible spectroscopy. How do I change the pH of 0.1M ...
0
votes
1answer
57 views

Why do we see complementary colors in UV/Vis Spectroscopy? [closed]

From what I read, a compound that absorbs visible light will produce a complementary color (using the color wheel), that can be seen. Why is this the case? Is it because, for example, if a molecule ...
0
votes
1answer
147 views

Spin-forbidden transition iof bromine

In one of the lectures of my spectroscopy course, the professor claimed that there is a strong absorption band in the UV/Vis spectrum of bromine, associated with a singlet-state to triplet-state ...
0
votes
1answer
80 views

Characterisation of gold-silver alloy nanoparticle

I have various compositions of gold-silver alloy nanoparticles. I would like to characterize my nanoparticles and confirm that they are alloys. Aside from the qualitative analysis of the colour and ...
0
votes
1answer
1k views

what the solution of this problem, negative absorbance values in UV-vis spectrum

In my project, I take the UV-visible spectrum of reaction between pyridinium chlorochromate and N-acetylcysteine. In some wavelengths, the absorbance value is negative for example it is (-0.006, -0....
0
votes
1answer
40 views

How to measure UV index? [closed]

I am a high school student so please apologise if I say something very dumb or irrelevant. I am conducting an experiment in which I want to find UV index at different points. Such as under shade, ...
0
votes
1answer
2k views

confusion about exocyclic double bond [duplicate]

I believe that there are only two exocyclic bonds in this structure. But in some text its mentioned as three. can someone clarify.