83
votes
Accepted
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 ...
- 17k
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 ...
- 11.5k
52
votes
A compound that absorbs all visible light
Substances which absorb almost all the light falling on them appear black. Therefore you are looking for the blackest known compound.
The record is currently held by Vantablack[1], a substance ...
- 15.1k
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).
...
- 42k
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 ...
- 36.1k
22
votes
A compound that absorbs all visible light
All metals are capable of absorbing photons of any wavelength below hard ultraviolet, as ideally there are allowed electronic transitions of arbitrarily small energy between states in the unfilled ...
- 27.4k
18
votes
Accepted
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 ...
- 68.7k
17
votes
Accepted
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. ...
- 36.1k
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 ...
- 3,002
16
votes
Accepted
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
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 ...
- 11.8k
15
votes
Accepted
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 ...
- 18.7k
14
votes
Accepted
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 ...
- 15.1k
14
votes
Accepted
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 ...
- 43.1k
14
votes
Accepted
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.
...
- 68.7k
14
votes
Accepted
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 ...
- 28.1k
14
votes
Accepted
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 ...
- 36.4k
13
votes
Accepted
Are the bonding orbitals in methane equivalent - photoelectron spectrum
This question goes along the line of what does it mean when it is said that an sp3 orbital has 25% s-character. It also intrigued me so I have tried to find answer, which would not break my hybridised ...
- 4,457
13
votes
A compound that absorbs all visible light
Any black compound absorbs photons in all the visible spectrum; that is why essentially it appears black to our eyes. So, for instance, iron(II,III) oxide, $\ce{Fe3O4}$ will do so; it is even used as ...
- 18.7k
13
votes
Accepted
1H (proton) NMR spectra for alkanes
Unfortunately, although the answer given by bon provides a very simplistic answer to a fairly common NMR-101 problem, it is not quite correct. It is fine for the propane case, but falls short for ...
- 11.8k
13
votes
Accepted
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 ...
- 68.7k
13
votes
Accepted
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 ...
- 4,530
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 ...
- 19.8k
12
votes
In infrared spectroscopy, why is there no C=C reading for E alkenes?
The $\ce{C=C}$ stretch is responsible for this ir peak. For an ir absorbtion to occur, the absorption must result in a change in dipole moment. If we examine the $\ce{C=C}$ stretch in cis- and trans-...
- 83.1k
12
votes
Are the bonding orbitals in methane equivalent - photoelectron spectrum
The short answer is that's not how photoelectron spectroscopy works. It's a one-photon spectroscopy.
You have a sample of $\ce{CH4}$ in this case, and you shoot different energy photons at the sample....
- 27.3k
12
votes
Accepted
In spectroscopy, is it possible for the sample to be excited multiple times?
Very technically? Yes.
Realistically? The probability is small enough that even if it does happen, the peaks for the multiple transitions are going to be small enough that we cannot really observe ...
- 2,045
12
votes
Accepted
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 ...
- 30.4k
12
votes
Accepted
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 ...
- 16.9k
Only top scored, non community-wiki answers of a minimum length are eligible