84
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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 ...
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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 ...
- 11.6k
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).
...
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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 ...
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 ...
- 39.1k
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 ...
- 71.1k
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. ...
- 39.1k
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 ...
- 3,050
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 $C_2$ ...
- 1,909
15
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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 ...
- 11.9k
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.
...
- 71.1k
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 ...
- 18.9k
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 ...
- 15.3k
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 ...
- 43.8k
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 ...
- 30k
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 ...
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13
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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 ...
- 11.9k
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 ...
- 2,100
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 ...
- 71.1k
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 ...
- 5,020
13
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 ...
- 20.8k
12
votes
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Why is it possible to image LUMO if these orbitals are, by definition, unoccupied?
Why not? It's not like we poke them with our finger, anyway. All we can really see are the electron transfers. Now, the transfers from the molecule are as good as the transfers to it. If we adjust our ...
- 31k
12
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Why does the carbonyl group in an acid anhydride have two stretching frequencies?
The two observed C=O frequencies are due to the symmetric and asymmetric stretching modes of the anhydride.
Source: Introduction to Spectroscopy, Pavia and Lampman
You can see that the lower ...
- 17.1k
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 ...
- 67.3k
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 ...
- 43.8k
11
votes
Accepted
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 ...
- 17.1k
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-...
- 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 ...
- 30k
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,...
- 12.9k
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