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.
87
questions
0
votes
0answers
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 ...
4
votes
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 ...
3
votes
3answers
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 ...
0
votes
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....
1
vote
0answers
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 ...
1
vote
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 ...
1
vote
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 ...
2
votes
0answers
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 ...
1
vote
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 ...
3
votes
0answers
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{...
1
vote
0answers
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 ...
5
votes
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 ...
4
votes
0answers
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 ...
0
votes
0answers
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 ...
0
votes
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)? ...
2
votes
0answers
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 ...
0
votes
0answers
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 ...
2
votes
0answers
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, ...
1
vote
0answers
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 ...
1
vote
0answers
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 ...
2
votes
0answers
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 ...
4
votes
1answer
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 ...
0
votes
0answers
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 ...
1
vote
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.
...
0
votes
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 ...
1
vote
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 ...
3
votes
0answers
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 ...
1
vote
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 ...
0
votes
0answers
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) ...
1
vote
0answers
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
...
0
votes
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 ...
1
vote
0answers
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 ...
0
votes
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 ...
1
vote
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, ...
1
vote
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 ...
2
votes
0answers
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 ...
8
votes
2answers
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 ...
1
vote
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 ...
0
votes
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....
1
vote
0answers
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 ...
2
votes
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:
$$ k= (\frac{ΔE_{vib} *2π}{h})^2 µ$$...
1
vote
0answers
39 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 $40^\circ\text{C}$). ...
5
votes
0answers
66 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 ...
2
votes
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 ...
2
votes
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'-...
7
votes
2answers
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 ...
5
votes
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 ...
1
vote
0answers
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 ...
0
votes
0answers
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 ...
0
votes
0answers
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 ...
