Questions tagged [photochemistry]

Photochemistry is a branch of chemistry concerned with the chemical effects of ultraviolet, visible, or infrared radiation.

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19
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304 views

Some materials emit more photoelectrons than others - why?

Again, I'm a physicist turning to chemists (so bear with me). So I've been measuring some materials by changing the wavelength of the incident light on the material and I have a detecting tip like in ...
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1answer
309 views

What might serve as an initial starting photocatalyst for this large water-splitting solar simulator?

Question: What might serve as an initial starting photocatalyst for this large water-splitting solar simulator? Surely there must have been some planned experiments! The Gizmodo article Insane Light ...
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823 views

Finding the wavelength of maximum absorption of Tartrazine using Fieser-Kuhn

How would you use Fieser-Kuhn rules to calculate the wavelength of maximum absorption for tartrazine? Fieser-Kuhn rules states that: $\lambda_{max}=114+5M+n(48-1.7n)-16.5\ R_{endo} - 10\ R_{exo}$ ...
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1answer
378 views

Does liquids that emit light when vibrated exist?

I am looking for a liquid that illuminates when vibrations are added. It does not have to be strictly chemical, it might as well be something else as well. Maybe a crystal in powder form mixed with ...
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87 views

Mechanism of photolysis of HX

What is the mechanism for the photolysis of $\ce{HX}$ to dihydrogen and dihalogen ? From the low quantum yield (0.3% for $\ce{HI}$ according to one paper) it seems unlikely to be a chain process but I ...
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87 views

Why does ethene not disintegrate upon excitation?

The average c=c double bond has somewhere around 614 kJ/mol of energy, if we convert it to eV, then the bond strength is roughly 6.4 eV. Additionally, Ethene absorbs light at 171 nm. However, if we ...
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29 views

Further reading on photoconductivity of hemoglobin

I recently ran into this paper which describe experiments that confirm that hemoglobin is photoconductive. Finding this fact as incredible, I wanted to read up more on photoconductive properties of ...
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103 views

Why do old black and white photos fade?

I understand why photos based on organic dyes would fade (discussed previously). But photos based on metallic silver fade as well such as like the one shown below. As a metal (a fairly stable one at ...
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549 views

Interpretation of PES spectra

Given that both elements are in the same period, what information from the PES spectra indicates that oxygen would have a smaller atomic radius? (A) The number of peaks (B) The intensity of the peaks (...
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305 views

Relative energies of singlet and triplet states in Jablonski diagrams

In a Jablonski diagram, we have singlet and triplet excited states where spin is conserved or changed, respectively. My book says any singlet excited state is found to have higher energy than the ...
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49 views

Are there any ways of modifying molecules to increase their probability of two photon absorption?

While checking two photon microscopy, the use of high flux femtosecond laser is required for the dual absorption of photons, due to the low probability of these two photons being absorbed. Is there ...
3
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66 views

How to calculate the quantum yield of a photochemical process?

I have that $\pu{100 ml}$ of an aqueous solution containing $\pu{1.0 mM}$ $\ce{H2O2}$, $\pu{100 mM}$ $\ce{CH3OH}$ and $\pu{200 mM}$ DMSO are exposed to monochromatic light with a wavelength of $300$ ...
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80 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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54 views

Rate constants and their relationship to quantum yields

Question A dye molecule has a singlet excited state lifetime of $\pu{0.85 ns}.$ The quantum yield of triplet formation is $35~\%.$ What is the rate constant for intersystem crossing from the ...
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219 views

Is it possible to arrest the post-actinic effects of photodegradation in ABS polymers?

Polymers like acrylonitrile butadiene styrene (ABS) are adversely effected by UV exposure, both visually (by yellowing) and with regard to other material properties [1]. What's worse is that the ...
3
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110 views

How can I preserve chlorophyll for long periods of time?

I'm currently working on a XIX century photographic process called Anthotype. It relies on organic colored substances that fade when exposed to sunlight. For the substances I've tried alcoholic ...
3
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160 views

Mechanism of photochemical hydroamination with LDA

I've recently come across a couple examples of intramolecular alkene hydroamination accomplished by treatment with LDA followed by visible light irradiation (tungsten light bulb):[1,2] I'd assume ...
3
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287 views

Is there a catalyst for the decomposition for hydrogen peroxide that speeds it up but still makes the reaction light dependent?

I am building a Rube Goldberg machine for Science Olympiad, and one of the scoring steps is to use light to trigger a chemical reaction, which made me immediately think of the decomposition of ...
3
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136 views

Spectra of Methylene Blue

Does the spectrum of Methylene Blue change on prolonged exposure to light? I've studied about the photochemical reactions and about energy transfer reactions. Methylene Blue is a triplet sensitizer ...
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514 views

How does a photochemical reaction of lignin with oxygen (yellowing of paper) produce chromophores?

Edit: This question is about chromophore production in lignin as found in low cost or short-term use paper such as newsprint. A different, excellent answer describes oxidation yellowing of the ...
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33 views

Predicting a route to use chloride as a reducing agent for titanium dioxide under UV

In my lab we are deadlocked on a seemingly simple problem. We would like to find some reaction where $\ce{Cl-}$ can be used as a reducing agent on $\ce{TiO2}$ in a UV photosynthesis. We ideally want ...
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99 views

Why might the ratio between two Q-band peaks in ZnTPP decrease with increasing temperature?

In ZnTPP (Zinc tetraphenylporphyrin), there are two Q-band emission peaks. When I run steady state emission measurements at different temperatures, the ratio of their respective peak intensities ...
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118 views

Photoelectrochemical (PEC) water splitting

I'm starting to prepare for my research project on photoelectrochemical (PEC) splitting of water into H and O using (F doped) titanium dioxide as the photoanode. I've been unsuccessfully searching in ...
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What is the reaction steps taken when producing auroral forcing?

As described in here: https://www.nasa.gov/feature/goddard/2018/sounding-rocket-mission-will-trace-auroral-winds A mixture of Trimethylaluminium, Barium and Strontium reacts and ionize in the upper ...
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42 views

What is the difference between "primary quantum yield" and quantum yield?

The definition of the primary quantum yield given in Atkins textbook Physical chemistry as "The primary quantum yield, φ, is defined as the number of photophysical or photochemical events that ...
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Cause of photoluminescence in CaV2O6

I had prepared the sample of Cav2O6 using solid-state reaction route. I had done XRD, SEM-EDS which all matched with the previous results. There was something strange when I did the PL analysis. I saw ...
2
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121 views

Cyanotype photography with potassium ferrocyanide

Some years ago, due to a translation error that I only discovered later, I made cyanotypes using a mixture of ammonium ferric citrate and potassium ferrocyanide instead of ferricyanide. This worked, ...
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30 views

Where can I look for a short chain photopolymer?

I am by no means an expert in this field, so please be patient with my explanation. I am looking for a photopolymer with very specific properties. I am not sure how realistic it is to find such a ...
2
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59 views

Would the Formation of Benzaldehyde Be Possible Under Specific Conditions?

Our process: We cure an epoxy resin using SLA. The triarylsulfonium hexafluoroantimonate salts in propylene carbonate act as the photoinitiator for the oligomeric reactions between 4,4 ...
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65 views

Could UV lasers be used to split CO2 and H2O?

I was wondering whether intense UV light, tuned to the correct wavelength, could be used to split carbon dioxide and water molecules as a first step towards synthesizing liquid fuels.
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32 views

Hybrid thin films containing azobenzene with reversible photoresponsive behavior

I am going to prepare hybrid thin films containing azobenzene with reversible photoresponsive behavior. I have read about different combinations of inorganic layers such as layered double hydroxide (...
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74 views

What are 1A_g and 1B_u excitons?

I was going through a paper on organic LED chemistry [1]. I saw that the authors referred to "$1A_g$" and "$1B_u$" excitons (and also "$2A_g$" and "$2B_u$" excitons), terms which I don't really ...
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68 views

Investigating the displacement of a Se anion by a Sulphide anion

I am working with CdSe Quantum Dots suspended in hexane. I then tested the photoluminescence of my solution. Then I mixed my CdSe dots with a mixture of an organic conducting polymer which was ...
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240 views

How to model iso-surface of molecular orbitals of singlet and triplet excited states

I've modelled the iso-surface of the highest occupied molecular orbital of a molecule with DFT in Gaussian.If I were to model the iso-surface of the molecular orbital of the singlet and triplet ...
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104 views

Calculating photolysis time of AgF

How can I theoretically predict the time needed to photolyze n moles of $\ce{AgF}$? (with UV) (this is not a homework question) The photolysis of $\ce{AgF}$ requires UV light - but I don't know which ...
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39 views

Photochemical versus Photophysical

What is the difference between the terms photochemical and photophysical properties? What are some examples from each category?
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44 views

electronic transition for polyenic molecules

I am having troubles with polyenes states symmetry. I found an exercise on the pentadien, where they ask us to analyze the symmetry of the singlet excited states corresponding to: State S1: π+ →π+ ...
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35 views

Use chlorophyll a Galvanic cell to create hydrogen and electricity

What if we want to take chlorophyll in a container and put it into light . Then chlorophyll will lose electrons and will become positive itself then we will have a solution of negatively flowing ...
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397 views

Can static electricity damage solar cells?

How does static electricity damage common solar cells making them less photo reactive? At watt voltage and/or amps would change the chemistry of the common solar cell? I want to think that as long ...
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32 views

Why photons with longer wave length demonstrate more active scatter and transmit that shorter length?

Why photons with longer wave length demonstrate more active scatter and transmit that shorter length? This troubles me to understand why NIR and Infra-Red goes through diffused media when compared to ...
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292 views

How do you make photoresist/photohardening paint?

I have been looking into making my own PCB's, but I noticed there is little information on making photo hardening paint. This is a critical component when etching the circuit, and I am very curious on ...
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58 views

Why do ionisations from non-bonding orbitals result in little/no vibrational structure in a photoelectron spectrum?

I understand that ionisations from bonding and antibonding orbitals create vibrational structure from the Franck-Condon principle, resulting in a greater overlap integral between different vibrational ...
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64 views

Excitation Source for visible emitting Quantum dots

I read that the best excitation source for visible emitting quantum dots is UV light of wavelength $\mathrm{360~nm}$ to $\mathrm{380~nm}$. But why should the excitation source have lower frequency ...
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53 views

Is there any porous material that can have narrow parallel and "perfectly straight" cavities/holes through it (or bored through it)?

I'm basically looking for a material that can allow photons to pass through its cavities, but only those photons that travel at an angle (almost) exactly perpendicular to the materials surface. Non-...
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41 views

Why does increased conjugation in a molecule cause the wavelength absorbed to decrease (i.e. why does a red-shift occur)?

I was recently looking at a paper about novel organic dyes for efficient dye-sensitized solar cells and one point the authors made was that out of the two dyes mentioned the one with a larger pi-...
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21 views

question about photodamage on plastic

I know that plastic are susceptible to UV attack. They create free radicals when put under sunlight even when kept for a short time. I'd like to know if the photo-damage will stop once it is taken ...
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Organic Based Photocathode

What organic molecules have a relatively small work function, preferably in the visible spectrum? Polycyclic aromatic hydrocarbons are in the low UV spectrum, making it unsuitable for the photocathode ...
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33 views

Titanium Dioxide and plastic

How would you recommend attaching a film of anatase to a flat polycarbonate surface without compromising its photocatalytic characteristics? The self cleaning paints that I have seen are generally ...
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54 views

Photoelectric effect question

My attempt:- 1)At 0.68e15 Hz frequency of light,Metal A gives 7.2eV Kinetic Energy(KE). 2)At 1e15 Hz frequency of light, Metal B, gives 6eV Kinetic Energy. 3) At 1.1e15 Hz frequency of light, Metal ...
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43 views

Why isn't hydrochloric acid typically made via the photochlorination of hydrogen?

I understand that in large quantities the reaction is explosive but couldn't the flow of gas just be regulated to control the reaction? It seems like producing hydrogen chloride like this then ...