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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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An investigation on the rate of degradation (in %) of Chrysoidine-Y dye, as measured by UV-Vis spectrophotometry

Planning to do an investigation on the rate of degradation (in %) of Chrysoidine-Y dye, using UV-Vis spectrophotometry. I am planning to take an approach of increasing the concentration of Hydrogen ...
Ronith's user avatar
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Do σ→π* and/or π→σ* transitions occur in ultraviolet spectroscopy?

I was taught that the only transition that occur in UV-vis spectroscopy are: σ→σ* π→π* n→π* n→σ* Wikipedia seems to support this claim but I have trouble understanding why this must be the case. ...
Frisk17's user avatar
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UV-vis spectra - maximum absorption

If I have a noisy UV-vis absorption band, how do I determine the maximum absorption? Do I look for the highest absorbance value or do I look for the most intense band and take the value from the ...
Mike's user avatar
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UV-Vis spectrum of alkane

My reference books stated: Methane's maximum absorption wavelength is 125 nm, ethane's is 135 nm. The longer the carbon chain, the larger the absorption wavelength, it is 165 nm for n-octane. Well, ...
Shira's user avatar
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UV-Vis spectrum of 1,3-butadiene

Today I had the first lesson about UV-Vis spectrum. From the picture, the transition from HOMO to LUMOs of 1,3-butadiene depends on whether the structure is s-trans or s-cis. My question is: Why the ...
Shira's user avatar
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155 views

N2 HOMO-LUMO Gap calculation

I am thinking about calculating the HOMO-LUMO energy gap for $\ce{N2}$ molecule. I thought I could model this as a particle in a box problem to find $E_\text{HOMO}$ and $E_\text{LUMO}$. The formula I ...
cows's user avatar
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Is there any uv-vis sensor that installs on a pipe like other measurement tools like flowmeter or temperature sensor?

I am looking for an industrial UV-vis sensor that is installed on a pipe like other measurement instruments like temperature and flow transmitters. I researched this subject and I found one model but ...
jasw's user avatar
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How can you find the Absorption of a specific compound in a solution with 2 other compounds using Uv spectrophotometer

I was wondering if there was a way to get the absorption of ascorbic acid in a solution with citric acid and disodium hydrogen phosphate? I’m thinking of measuring the absorption of disodium hydrogen ...
Benjamin's user avatar
1 vote
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120 views

Cation/Anion UV-Vis absorption

I want to understand how the ground state absorption of a molecule shifts if an electron is added or removed. I found these two publications 1 and 2 that observe shifts, but both times a redshift, be ...
Martin 's user avatar
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UV-Vis Absorption Spectra climbing at lower wavelengths

I have run a sample of Pyrene in Ethanol and got a UV Vis absorbance spectra that starts climbing as it reaches the lower wavelengths. I am using quartz cuvettes and was wondering what could be the ...
Ashwin's user avatar
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UV-Vis Absorbance against wavelength graph for finding max wavelength

I have plotted the absorbance against wavelength graph to find the optimum wavelength for maximum absorbance of p-nitroaniline. However, the curve (dark blue) of the most concentrated solution (sample ...
joe 's user avatar
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2 answers
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Datasets of Light Absorbance Spectra for Atmospheric Gases

I am currently doing some thermal/aerospace engineering research that involves finding light absorption in different points in Earth's orbit. What is the best way to find absorbance vs. wavelength ...
Ankit's user avatar
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1 answer
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Is vibronically resolved spontaneous emission temperature dependent, following a distribution defined by the canonical density operator?

Does the lifetime of a molecular excited electronic state, for example the $S_1$ state, suffice for thermal equilibration before spontaneous emission occurs? For example the fluorescence of coumarine, ...
Hans Wurst's user avatar
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How can I compare the UV/Vis absorption difference after metal ion chelating of crown ether-containing polymer?

Recently I have synthesized the polymer that contains 1-aza-18-crown-6 in the repeating unit. I want to know if there is any UV/Vis absorption difference after the chelation of metal ion. Considered ...
Krang Lee's user avatar
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Auxochromic action of an alkyl group attached to a double bond

In the UV-Vis spectra, $\ce{CH2=CH2}$ has max absorbance at $\pu{171 nm}$. $\ce{CH3-CH2-CH=CH-CH2-CH3}$ has max absorbance at $\pu{184 nm}$. The alkyl groups decrease the π-π* gap by raising the π but ...
Aadithya Varma's user avatar
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The extinction coefficients of oxymyoglobin and ferryl myoglobin

I want to know what the extinction coefficients of oxymyoglobin and ferryl myoglobin are. I was able to find the one for the oxymyoglobin in this pretty old article (it says that it equals $121 \text{...
ChemistryGeek's user avatar
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UV absorbance titration to determine binding stoichiometry

I previously posted a question but I think I did not explain correctly. I want to construct a Job plot using UV-Vis titration to find binding stoichiometry. I have 20uM of ligand solution and 20uM of ...
dojodna's user avatar
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Comparison of two different coloured dyes using UV-vis spectra

I know that Both solutions are a shade of purple due to the lack of absorbances in the red and blue regions, however am I correct in thinking that the peak slightly to the right of the 2 in this ...
Aurora's user avatar
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1 answer
156 views

Assigning structure based on EPR spectroscopy

When given two copper(II) complexes - bis(N-3-chlorophenyl-salicydenaminato)copper(II) and bis(N-3-methylphenyl-salicydenaminato)copper(II) - how can you predict their EPR spectrum and hence their g ...
qwerty09's user avatar
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1 answer
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Absorption wavelength of nickel (II)

One of my students is trying to study a nickel(II) solution, prepared from nickel(II) sulfate, which is green. In solution it is also green, thus I would expect it to absorb red light. Here is a test ...
Rafael's user avatar
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Crude palm oil DOBI analysis

I'm performing Crude Palm Oil DOBI spectrum analysis using uv-1900i UV-VIS spectrophotometer at a range of 269nm and 446nm but it's only giving peak absorbance at 446nm but no reading at 269nm,what ...
NICKSON MATUU's user avatar
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Searching for electronic spectroscopy reference book

I'm looking for a reference book that will help me describe UV-VIS spectra of organic compounds in terms of Q band, MLCT band, Soret band, and so on. Is something like that available? Thanks
farmaceut's user avatar
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Creating custom spectra graphs

I wanted to make a few custom spectra graphs for some homework questions I'm assigning. The issue is that the Education Board issued datasheets do not reflect online images. They often say that bonds ...
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Spectroscopic methods for quantifying peptides/proteins with or without Tryptophan or Tyrosine content

I have several peptides (20-50 amino acids long) which I want to quantify the solubility/concentration in a solvent at certain temperature and pH. These peptides may or may not contain Tryptophan or ...
littleworth's user avatar
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458 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 ...
Ann Ivanov's user avatar
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1 answer
488 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 ...
StrugglingChemistryStudent's user avatar
3 votes
3 answers
620 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 ...
Yak's user avatar
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1 answer
831 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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1 answer
384 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 ...
Mikkel Rev's user avatar
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2 answers
644 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 ...
Mikkel Rev's user avatar
2 votes
0 answers
57 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 ...
dogman's user avatar
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3 votes
1 answer
2k 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 ...
Yakata's user avatar
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3 votes
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98 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{...
dogman's user avatar
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1 vote
0 answers
336 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 ...
MJAFort's user avatar
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6 votes
1 answer
4k 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 ...
fred_smith's user avatar
5 votes
0 answers
258 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 ...
Palamalama's user avatar
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153 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 ...
aerospace's user avatar
1 vote
2 answers
153 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)? ...
Gougni Adam's user avatar
2 votes
0 answers
154 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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2 votes
0 answers
79 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, ...
sarah bnm's user avatar
1 vote
0 answers
87 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 ...
Viraj's user avatar
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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 ...
sara's user avatar
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3 votes
0 answers
422 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 ...
Enric Ros's user avatar
4 votes
1 answer
2k 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 ...
excuse_dont_exist's user avatar
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0 answers
40 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 ...
user avatar
1 vote
2 answers
460 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. ...
Treex's user avatar
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1 vote
1 answer
926 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 ...
ibchemstudent's user avatar
1 vote
1 answer
221 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 ...
A small potato's user avatar
3 votes
0 answers
98 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 ...
uhoh's user avatar
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2 votes
1 answer
582 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 ...
E. Hunter's user avatar
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