Chemistry

Questions tagged [uv-vis-spectroscopy]

Ask Question

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

44 questions
Newest
Active
Bountied
Unanswered
Filter by
Sorted by
Tagged with
1
vote
0answers
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 $40^\circ\text{C}$). ...
4
votes
0answers
42 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 ...
1
vote
2answers
211 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 ...
7
votes
2answers
63 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 ...
5
votes
1answer
88 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 ...
1
vote
0answers
24 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 ...
0
votes
0answers
75 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 ...
0
votes
0answers
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 ...
1
vote
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 ...
2
votes
0answers
33 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 ...
1
vote
0answers
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 ...
2
votes
1answer
123 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 ...
6
votes
1answer
366 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, ...
8
votes
3answers
348 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 ...
1
vote
1answer
111 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 ...
4
votes
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, ...
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 ...
6
votes
1answer
58 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. ...
1
vote
0answers
31 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
vote
0answers
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 ...
0
votes
1answer
114 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 ...
4
votes
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 ...
0
votes
1answer
65 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 ...
3
votes
1answer
102 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 ...
-1
votes
1answer
119 views

What is the molar extinction coefficient of azorubine (carmoisine, E 122)

I'd be grateful for the molar extinction coefficient ε of azorubine at the absorption maximum (about 520 nm), with an authoritative reference.
0
votes
1answer
984 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
39 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, ...
2
votes
0answers
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 ...
-1
votes
1answer
249 views

Slope of Graph of Wave Number vs inverse square of the principal quantum number(1/n^2) in Hydrogen Emission spectrum

What is the final expression we get for wave number in a hydrogen emission spectrum? Let us say for example from 6 to an orbit $n$. Considering that it is an emission spectrum, I think it would be ...
-1
votes
1answer
64 views

Evidence for a chemical reaction

I know that the emission of light is evidence for a chemical reaction. However, are there any instances where emission of light can also be considered a physical reaction?
0
votes
1answer
981 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.
5
votes
1answer
416 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?
3
votes
1answer
187 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}...
1
vote
1answer
50 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 ...
0
votes
1answer
38 views

Angle of Light Source for Absorbance Spectroscopy

I apologize if this question is stupid, but have been puzzled by it for a few days. Say I have a spectrometer measuring in the visible light range and we're looking to measure the absorbance on a ...
1
vote
3answers
154 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
107 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 $\...
2
votes
0answers
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-...
3
votes
3answers
228 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 ...
4
votes
0answers
133 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 ...
7
votes
1answer
180 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 ...
0
votes
1answer
42 views

How to meausre ion interferences in solution?

Is there a way to quantitatively measure the interference of different metal ions in solution? I plan to measure concentration of Pb(II), Fe(II), and Cu(II) in solution together using a ...
12
votes
2answers
4k 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 ($\pu{253 nm}$...
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 ...