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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30 views

Relationship between transmittance and color of the solution

As I understand, transmittance is light which passes through a material and it determines the color of material (for example green solution transmits green light). Here’s the transmission spectrum of ...
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1answer
221 views

The reason for selection of wavelengths in the spectrophotometry of Quinoline Yellow SS

The absorption spectrum for Quinoline Yellow SS has peaks at 224 nm and 414 nm, and a trough at 337 nm. This experiment (see page 31), selects 224, 337 and 414 nm to be used in the spectrophotometric ...
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355 views

How to Combine an Emission spectrum into a colour? [closed]

I am trying to wrap my head around the flame test, and for the most part, it is making sense. My question is their a way to figure out the colour of a flame of an unknown element given the emission ...
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1answer
54 views

Finding the percent of light absorbed by a sample [closed]

I have an absorbance of $0.266$ and need to find the percent of light absorbed by the sample. Is it found by just turning it back into transmittence% and subtracting 1? So by that, would it be $(1 - 0....
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26 views

The mechanism of discoloration due to changes in the state of CP

I don't know the mechanism of discoloration due to phase change. https://pubs.rsc.org/en/content/articlelanding/2019/cc/c9cc02172h In the above paper, Cu(I) in CP1 (Figure 1 a) has a tetrahedral ...
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1answer
42 views

How to troubleshoot absorbance analysis when readings fluctuate

I am trying to measure creatinine in fluids by using an enzymatic (creatinine) test. I try to determine the concentration by the difference in absorbance before and after 5 minutes after a reagent is ...
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2answers
78 views

Is it false that the absorbance of two concentrations is the sum of the absorbances of the concentrations?

I am in the lab and trying to perform the molybdenum blue test for phosphorus using a photometer. It appears common speak in colorimetric lab sheets that Absorbance of a mix of two concentrations is ...
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47 views

What causes horizontal lines on an excitation-emission matrix in fluorometry?

I am doing excitation-emission matrices to test for CDOM, and we just got some brand new quarts cuvettes. When I hold them in front of a light, they're totally clear and clean. I ran a sample, and in ...
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1answer
336 views

How can I prove ascorbic acid degradation with Uv-vis spectroscopy?

I have to prove scientifically why a sodium ascorbate solution in water turns yellowish - reddish over time. I know ascorbic acid is supposed to oxidize into dehydroascorbic acid, and the latter then ...
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42 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{...
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22 views

Absorption Curves Normalization

I have absorption curves for three species that are nominally the same concentration that I need in order to calculate spectral overlap. Part of that process is dividing the curve through by the ...
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1answer
789 views

Why is 295 nm a good wavelength to check absorbance when testing for aspirin?

Take aspirin (acetylsalicylic acid) and hydrolyze it with NaOH. This results in sodium acetylsalicylate and water. I think the sodium is held on with an ionic bond, so it is really salicylate dianions ...
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53 views

Invisible spin allowed transitions in Tanabe-Sugano diagrams

In class we are looking at Tanabe-Sugano diagrams, more concretely at transitions for a d2 complex. I understand that the only spin allowed transitions are those that have a triplet state, therefore ...
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92 views

TD-DFT transition dipole moment vector does not align with experimental data

I have been modelling excited states of some molecules with similar stucture using TD-DFT theory, however, I have encountered an issue that sometimes transition dipole moment does not align with the ...
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2answers
63 views

Why iron(II) spectrometry is not measured in distilled water and it requires a complexing agent like o-Phen?

We know that iron(II) ions in water have a green colour. Why we cannot draw the spectrum of iron(II) directly in distilled water to measure the absorbance then determine the concentration of iron(II)? ...
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48 views

How to determine the number of π-electrons in a conjugated system from UV-Vis data?

Is there a way to determine the number of π-electrons in a conjugated system from UV-Vis data? I am modelling the electrons as particles in an infinite box of length $L$ equal to the length of the ...
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28 views

Absence of π–π* transitions with presence of CT transitions

An aromatic compound with a large number of delocalised electrons gives several distinct UV-vis absorption peaks, due to the many π–π* transitions that can occur. However, when complexed to transition ...
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43 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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40 views

What is the best way to clean Lovibond tintometer quartz cuvette used for oil?

I work in a laboratory where we regularly check edible oil color by using a Lovibond colorimeter. Some people suggested me to wash the quartz cuvette using soap solution. But I am thinking about ...
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119 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 ...
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197 views

How is the UV-visible spectra of carbonatotetraamminecobalt(III) nitrate interpreted?

In a laboratory practice I have done a characterization of the $\ce{[Co(NH3)4CO3]NO3}$ and obtained the following spectra: I don't know if the band between 300 nm and 400 nm can be due to the effect ...
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755 views

Why diethyl ether does not absorb in UV region?

Explain why diethyl ether does not have a UV spectrum, even though it has lone-pair electrons. Can we say that π* molecular orbital does not exist because there are no π-bonded electrons in diethyl ...
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37 views

Beer Lambert law when complex is tetragonal (Jahn-Teller elongated)

I wondered what modifications there would be to the Beer Lambert law to find the molar extinction coefficients for the solution if the solvent contained the ligands which bind to the metal centre of a ...
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2answers
102 views

Implications of the excitation spectra

The fluorescence excitation spectra show the change in fluorescence intensity as a function of the wavelength of the excitation light. I'm interested in the certain physical implications of the above. ...
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1answer
186 views

Is it possible to make a solution of zinc oxide in a high school chemistry lab?

As part of my IB Chemistry curriculum, we are required to conduct our own experiment researching our own question. I'm in the preliminary research phase and wanted to conduct an experiment looking at ...
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1answer
73 views

Is there an actual distinction between through-space charge transfer and excimer emission?

Variety of books and literature reviews consider excimer (or exciplex) emission something distinct from through-space charge transfer. Is this actually the case? This question arises, because the more ...
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81 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 ...
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1answer
134 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 ...
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62 views

Estimate the relative intensities of absorption given the split in energy levels

Estimate the relative intensities at $\pu{25 °C}$ of absorption originated in the ground state and the first excited state when the energy levels involved are separated by: (a) $\pu{10000 cm^-1};$ (b) ...
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49 views

Adsorption of Cu2+ using banana peels for pH 2,2.5,3,3.5,4

so basically I did my experiment which is the title. This is my procedure and results: Make 0.05M CuSO4 pipette 50ml CuSO4 change to respective pH values using HCl Add 2g of oven-dried banana peels ...
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1answer
698 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 ...
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40 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 ...
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1answer
810 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 ...
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2answers
356 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, ...
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1answer
94 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 ...
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84 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 ...
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549 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 ...
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1answer
33 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 ...
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1answer
82 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....
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22 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 ...
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1answer
627 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: $$ k= (\frac{ΔE_{vib} *2π}{h})^2 µ$$...
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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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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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2answers
689 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 ...
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1answer
46 views

Predicting color of a TMB derivative affected by peroxidase

The ELISA test on HIV works by verifying the presence of peroxidase within samples. The verification process is done through the enzymatic reaction that said peroxidase has on TMB (3,3',5,5'-...
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214 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 ...
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1answer
362 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 ...
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34 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 ...
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236 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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56 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 ...