26 votes

Is it possible for a substance to absorb a longer wavelength of EM wave and emit a shorter wavelength?

It is possible, but impractical. You can "upconvert" light. This effect, as Wikipedia relays, is due to the sequential absorption of two photons per emitted photon. This is certainly possible to make ...
Stian's user avatar
  • 2,785
19 votes

Is it possible for a substance to absorb a longer wavelength of EM wave and emit a shorter wavelength?

Yes it is possible for molecules to absorb a single photon at a longer wavelengths than some of those that they emit at. If the molecules are thermally isolated from their surroundings then the result ...
porphyrin's user avatar
  • 30.5k
15 votes
Accepted

Can reactions produce microwave or radio wave radiation?

An ammonia maser qualifies as an inorganic RF-emitting reaction. As the nitrogen changes position in the $\ce{NH3}$ molecule, ~24 GHz radiation is emitted. Similarly, organic methanol, $\ce{CH3OH}$ ...
DrMoishe Pippik's user avatar
14 votes

Is light a reactant in photochemical reactions?

It is neither reactant nor catalyst, and equilibrium concepts do not apply There are processes other than photochemistry that to go in a direction away from equilibrium. They require mechanical or ...
Karsten's user avatar
  • 40.3k
14 votes
Accepted

Is there any process that converts water into hydrogen and oxygen by using light and a catalyst?

Probably several of them. The one I found at the top with a search for "photocatalytic water decomposition" is Ref. [1]: The photocatalytic activity for water decomposition of alkaline ...
Oscar Lanzi's user avatar
  • 57.4k
12 votes
Accepted

Generation of singlet oxygen by irradiation

Rose bengal (pictured below) is a member of the fluorescein family. (image source: wikipedia) There are 3 steps in the process where rose bengal sensitizes the formation of singlet oxygen.. \begin{...
ron's user avatar
  • 84.8k
12 votes

What is special about the molecule luciferin that it can emit light?

[...] the protein luciferin is oxidized by the enzyme luciferase Luciferin is not a protein, but a benzothiazole with a thiazole attached to the carbon atom between nitrogen an sulfur. Upon ...
Klaus-Dieter Warzecha's user avatar
12 votes
Accepted

Effect of direct exposure to sunlight on various drugs

Conversion of D to L isomer or vice versa is about the last thing to worry about in this situation, even if it may be facilitated by sunlight to a significant extent (which I doubt). Also, storage of ...
Ivan Neretin's user avatar
  • 31.2k
11 votes

Effect of direct exposure to sunlight on various drugs

Isomerism is only one (and probably a minor) pathway. Many substances have chromophores that absorb light. Absorption leads to a high energy intermediate that is more reactive and able to access ...
Zhe's user avatar
  • 17.4k
10 votes

Oxidation of guanine with singlet oxygen

You're right that ground state $\ce{^3O2}$ doesn't undergo this reaction. There is no direct excitation of oxygen either. The key in these processes is the electronic excitation of tetraphenyl ...
Klaus-Dieter Warzecha's user avatar
10 votes

Does the carbon dioxide dianion exist?

The obvious Star Wars puns aside, I have never heard about the dianion of a carbon dioxide dianion and/or that it was named carbonite. However, the carbon dioxide radical anion, $\ce{CO2^{.-}}$, is ...
Klaus-Dieter Warzecha's user avatar
10 votes
Accepted

Lifetime components in phosphorescence decay

Phosphorescence should be at a longer wavelength than any fluorescence so carefully using a filter or grating should remove any fluorescence. Also measuring at different wavelengths will change ...
porphyrin's user avatar
  • 30.5k
9 votes

Material that absorbs only in NIR and emits in visible

Such materials not only exist but are common Most people will have seen an actual demonstration of materials that exploit the phenomenon of a substance that absorbs NIR light and emits visible light. ...
matt_black's user avatar
  • 36.2k
8 votes

Why are the absorption and emission spectra mirror images of each other?

The sketch below explains how the mirror image spectrum comes about. (the figure is not at all to scale, its just illustrative, but does show the salient features.) There are some conditions attached....
porphyrin's user avatar
  • 30.5k
8 votes

Why is absorbance spectrum continuous and not quantized?

The pictures you show are misleading as they refer only to molecules in the condensed phase. Isolated molecules in the vapour phase do have discrete (quantised) electronic, vibrational and rotational ...
porphyrin's user avatar
  • 30.5k
8 votes
Accepted

Photochemical reduction of benzophenone: why inverted flask?

I think the reason for inverting the the round flask is to capture sunlight very efficiently. A round bottomed flask filled with a fluid is like a ball lens. Sun rays can be considered parallel and ...
AChem's user avatar
  • 40.3k
7 votes

What is special about the molecule luciferin that it can emit light?

Klaus gave a nice summary on luciferin. The second part of your question was: Also, are there any chemical reactions which produce high energy electromagnetic waves, such as X-Rays? Any energy ...
Jan's user avatar
  • 68k
7 votes

Is it possible for a substance to absorb a longer wavelength of EM wave and emit a shorter wavelength?

There are indeed: we use them in "Laser Viewing Cards" to be able to see IR Laser. An example of such a card is presented below: When illuminated with IR light, it emits visible light. The principle ...
MMartin's user avatar
  • 87
7 votes

What is thermal plasma in-flight oxidation technique?

Original paper where this method (and, I guess, the term itself) has been introduced was written in Japanese in 1982 [1]. In 1997 there was a great overview published in English by Toyonobu Yoshida, ...
andselisk's user avatar
  • 37.7k
6 votes
Accepted

Photolysis of N-bromo compound in acidic conditions (radical cyclisation)

This is the Hofmann-Löffler-Freytag reaction, which was later examined by E. J. Corey (J. Am. Chem. Soc., 1960, 82, 1657-1668, DOI). When the reaction is performed in sulfuric acid, it is ...
Klaus-Dieter Warzecha's user avatar
6 votes
Accepted

Why can UV light initiate a reaction between hydrogen and chlorine gas?

Before going into the mechanism of this reaction, I suggest you look up free radical mechanism, as this reaction takes place through that. $\ce{Cl-Cl}$ bond in $\ce{Cl2}$ is weak enough to be broken ...
CupC_56's user avatar
  • 462
6 votes

Is it possible for a substance to absorb a longer wavelength of EM wave and emit a shorter wavelength?

What about (pure) rotational Raman spectroscopy? The specific selection rule is $\Delta J = \pm 2$. The anti-Stokes lines, with $\Delta J = -2$, arise from the emission of a photon with shorter ...
orthocresol's user avatar
  • 71.1k
6 votes
Accepted

Do conjugated polymers absorb very low energy photons?

In principle yes, longer conjugated regions absorb at longer wavelengths. The simplest model when thinking about this is to consider a particle in a box, or on a ring if considering cyclic conjugation ...
porphyrin's user avatar
  • 30.5k
6 votes
Accepted

Nitrogen dioxide fluorescence quenching and lifetime

You are looking for the rate constant $1/\tau^0=k_2$. The rate equation for the $\ce{NO2^*}$ is (using $N^*$ for $\ce{[NO2^*]}$ and N for ground state NO2), $\displaystyle \frac{dN^*}{dt}=-k_2N^*$ and ...
porphyrin's user avatar
  • 30.5k
6 votes
Accepted

Photochemical cycloaddition of ethene

For any pericyclic reaction (including cycloadditions), the key set of rules are the Woodward–Hoffmann rules. The rules are actually quite general, but people often first learn about them in the ...
orthocresol's user avatar
  • 71.1k
6 votes
Accepted

Does zinc oxide lose its UV blocking properties when mixed with oil?

$\ce{ZnO}$ is not soluble in oils. But it can form dispersion in oils. $\ce{ZnO}$ may react with traces of fatty acids in oils, forming respective zinc salts. But for UV screening context, it is ...
Poutnik's user avatar
  • 41.6k
6 votes

What is the reason of producing *spark* in the volcanic reaction (decomposition of ammonium dichromate)?

The mechanism of spark shining is the same as the mechanism of the orange glow in the core of the "volcano" - thermal radiation of solid bodies. Sparks are just dust particles of mostly ...
Poutnik's user avatar
  • 41.6k
5 votes

Why does the Förster resonance energy transfer scale as 1/r⁶?

The Forster (or resonance or dipole-dipole) energy transfer is a non-radiative transition between an electronically excited molecule and an acceptor. Non-radiative really does mean that no photons ...
porphyrin's user avatar
  • 30.5k
5 votes

Why does the energy gap for π - π* transitions shrink with the size of the pi-conjugated system?

The simplest physical picture is surely that of a particle in a box. (Of course its more complicated otherwise we would not need to do accurate quantum calculations but this model retains the basic ...
porphyrin's user avatar
  • 30.5k

Only top scored, non community-wiki answers of a minimum length are eligible