84 votes
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Is it true that heavy water is not blue?

Based on your description, I may have found the article you originally saw, or at least one very similar. Researchers from Dartmouth College published a paper$\mathrm{^1}$ in which they report, among ...
airhuff's user avatar
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69 votes

Is it true that heavy water is not blue?

This does seem to be the case. I don't have images of the different types of water, but I did find this overlaid IR-visible spectrum of water and heavy water: As you stated, the presence of deuterium ...
Tyberius's user avatar
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52 votes

Can hot food ever emit x-rays or gamma rays?

In theory, yes, you can heat objects to a high enough temperature to emit x-rays or gamma rays. You cannot do this to food, and you certainly cannot do this in your kitchen (or probably any kitchen). ...
Ben Norris's user avatar
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31 votes

Can hot food ever emit x-rays or gamma rays?

It has nothing to do with what you were going for, but there is a small, but non-trivial amount of x- and gamma-ray output for most food and so the answer is trivially "yes". In particular any food ...
dmckee --- ex-moderator kitten's user avatar
27 votes

Why does hydrogen burn with a pale blue flame while its emission spectral lines are red in colour?

It is a very interesting question, but comparing a combustion spectrum with an atomic emission one is like comparing apples and oranges. A flame is a luminous gas phase chemical reaction where the ...
AChem's user avatar
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18 votes
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Why does the C–C bond have extremely weak absorptions?

For vibrational spectra the primary transition under investigation is the $v = 1 \leftarrow 0$ excitation (because $\hbar\omega >> k_\mathrm{B}T$, so excited states have negligible thermal ...
orthocresol's user avatar
17 votes
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Difference between a "cartoon" flame test and a "real" flame test? How do chemists do flame tests correctly?

Your interest is greatly appreciated. As a first step, let's clarify that flame tests as an analytical tool are obsolete. No professional chemist will use them to identify a given unknown sample. ...
AChem's user avatar
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16 votes

How do I determine the molecular vibrations of linear molecules?

As Tyberius noted, the projection formula does not work for infinite order groups (this is because the Hermitian form on characters is defined to be G-invariant by averaging over all elements in a ...
levineds's user avatar
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16 votes
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Relationship between the symmetry number of a molecule as used in rotational spectroscopy and point group

This is not in general true Consider molecules a point group not containing inversion symmetry, e.g. $C_2$ hydrogen peroxide The $C_2$ group has only two elements, $E$ and $C_2$, and the $C_2$ ...
user213305's user avatar
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15 votes

Why is tetramethylsilane (TMS) used as an internal standard in NMR spectroscopy?

TMS was first proposed as a reliable internal chemical shift reference in 1958 by Tiers. Back in them good ol' days, 1H NMR was called proton nuclear spin resonance, or nsr, and the tau scale was ...
long's user avatar
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15 votes
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Why don't equivalent hydrogens cause splitting in NMR?

I will provide a full quantum mechanical explanation here.[1] Warning: rather MathJax heavy. Hopefully, this lends some insight into how the diagrams that long and porphyrin posted come about. ...
orthocresol's user avatar
15 votes
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Comparing the experimental and calculated UV/vis spectra for ethene

In short, there are two obvious problems with the setup OP uses for TD-DFT calculations: B3LYP functional is not a good choice for TD-DFT. 6-31G(d) basis is usually too small. At M06-2X/Def2-TZVP ...
Wildcat's user avatar
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14 votes
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Why is tetramethylsilane (TMS) used as an internal standard in NMR spectroscopy?

TMS has 12 protons which are all equivalent and four carbons, which are also all equivalent. This means that it gives a single, strong signal in the spectrum, which turns out to be outside the range ...
bon's user avatar
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14 votes
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What is the correct way to verify a structure's geometry, for example for benzene?

A deviation within the low picometres is nothing to worry about, there are many reasons for this. Primary literature, like peer-reviewed journals, will always publish an analysis of the obtained ...
Martin - マーチン's user avatar
14 votes
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Uv vis and fluorescence spectroscopy: sensitivity

Fluorescence is a 'zero background' or absolute type of measurement meaning that single photons can be measured against a 'dark' background so the sensitivity is huge, and limited by the fraction of ...
porphyrin's user avatar
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14 votes
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Looking for a dye which emits around 680 nm

There are two dyes commonly used in biochemistry research with $\lambda_\mathrm{Ex}$ of around $\pu{650 nm}$. They are Alexa Fluor 647 from ThermoFisher and Cyanine5 (Cy5) from Lumiprobe. Two example ...
Mathew Mahindaratne's user avatar
14 votes

Reconstruction of NMR spectrum by entropy maximization (MaxEnt)

The entropy in "maximum entropy" refers to the information entropy concept as introduced by Shannon. The MaxEnt technique referred to by Hoch may be regarded as cosmetic because what it does ...
Buck Thorn's user avatar
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13 votes

Why don't equivalent hydrogens cause splitting in NMR?

The first important point to note is that magnetically equivalent nuclei do in fact couple to each other, however no splitting is observed in the spectrum. The second point is that chemically ...
long's user avatar
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13 votes
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What is a virtual state?

In most Raman experiments, the incident radiation is not near (or at) an absorbing wavelength, and so you will never access a real, honest-to-God excited state (stationary state). (If it was close to ...
jjgoings's user avatar
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13 votes
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Derivation of the Orgel diagram for octahedral d2 complexes

1. Weak-field and strong-field limits I will adopt the description used in Figgis and Hitchman's Ligand Field Theory and Its Applications (p 5), because I cannot really phrase it better: It is ...
orthocresol's user avatar
13 votes
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What is the difference between quantities reported as optical rotation and circular birefringence?

It gets very complicated, there are many papers and books on the topic and this little table, from Jensen et al. 1, gives a glimpse of the anisotropic effects: An extremely short answer is this: when ...
Ed V's user avatar
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12 votes

How to determine the structure of organic molecules without spectroscopy

One thing that was well known, even in the early days, was elemental analysis. It is Justus von Liebig’s contribution to have worked out the sum formulae of hundreds of natural compounds. This ...
Jan's user avatar
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12 votes
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"NBO diagrams" versus MO diagrams

A molecular orbital diagram is a schematic representation of how we interpret bonding in certain species. It is as much an accurate representation for a specific bonding situation as a Lewis structure ...
Martin - マーチン's user avatar
11 votes
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Modern open-source tools for simulation of NMR spectra

In Org Biomol Chem 2016, 14, 3943, Goodman reports the replacement of some "tradition" (expensive) programs with free/open-source ones, as applied to their dp4 method. Specifically: Molecular ...
NotEvans.'s user avatar
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11 votes

Is it true that heavy water is not blue?

If you saw it during the 1990s online era, it might well have been reference links on my old website, from this article on physics misconceptions in grade school. I'd been doing some textbook-...
wbeaty's user avatar
  • 401
11 votes

Why are some molecules unable to absorb infrared radiation?

In basic terms, for a molecule to absorb radiation there has to be an oscillating dipole being produced. This can occur by nuclear motion (vibrations, rotations) or electronic motion to produce ...
porphyrin's user avatar
  • 30.4k
11 votes

Confusion on light absorption by electrons

Depending on how large the value $y$ is, the premise of your question can be wrong. On the other hand, if you jump between two electronic energy levels where $y$ is on the order of vibrational states,...
jheindel's user avatar
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11 votes
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Terminology of atomic spectroscopy: Difference Among Term, States and Level

The figure below shows the situation between configuration for a $p^2$ configuration, terms, levels and states. The word 'state' tends to be used colloquially to mean any of Term, Level or State. ...
porphyrin's user avatar
  • 30.4k
11 votes

Is it safe to look at a mercury gas discharge tube?

Could it have caused irritation or injury? Possibly, but not likely, depending on a few factors: The intensity of the emitted ultraviolet. Proximity to the light source. Length of exposure. You'd ...
DrMoishe Pippik's user avatar

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