Questions tagged [molecules]

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118
votes
5answers
30k views

What does it mean for two objects to “touch”?

If you've ever been annoyingly poked by a geek, you might be familiar with the semi-nerdy obnoxious response of "I'm not actually touching you! The electrons in the atoms of my skin are just ...
21
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2answers
3k views

In counting degrees of freedom of a linear molecule, why is rotation about the axis not counted?

I was reading about the equipartition theorem and I got the following quotations from my books: A diatomic molecule like oxygen can rotate about two different axes. But rotation about the axis down ...
21
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8answers
6k views

Can a single molecule have a temperature?

A show on the weather channel said that as a water molecule ascends in the atmosphere it cools. Does it make sense to talk about the temperature of a single molecule?
163
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3answers
37k views

How does a knife cut things at the atomic level?

As the title says. It is common sense that sharp things cut, but how do they work at the atomical level?
0
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3answers
4k views

Potential energy curve for intermolecular distance

(source: a-levelphysicstutor.com) I'm trying to understand this curve better, but I can't quite figure out what "negative potential energy" means. The graph should describe a molecule oscillating ...
13
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5answers
25k views

Water in vacuum (or space) and temperature in space

So, water in vacuum will boil first and then freeze. I don't know how the freeze happens. As pressure lowers to zero, what happened to freezing point? (I know heat taken by vapor, and the water cool ...
7
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3answers
10k views

Book recommendation for Atomic & Molecular physics

What are some interesting books for a sophomore undergrad about Atomic & Molecular Physics?
50
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3answers
2k views

Are there exact analytical solutions to the electronic states of the hydrogen molecular ion $\mathrm H_2^+$?

The hydrogen molecular ion (a.k.a. dihydrogen cation) $\mathrm H_2^+$ is the simplest possible molecular system, and as such you'd hope to be able to make some leeway in solving it, but it turns out ...
13
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4answers
54k views

What is the resonant frequency of liquid water?

I learned it's not 2.45 GHz. But what is it, then? In my failure to find the real value, I'm starting to wonder: does it even make sense talking about a resonant frequency of water molecules?
3
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3answers
1k views

How to understand the symmetry $\Sigma^-$ in the wavefunction of a diatomic molecule?

In Wikipedia (and elsewhere), a particular symmetry of the quantum system of a diatomic molecule is mentioned: symmetry under reflection along a plane containing the internuclear axis. The ...
2
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1answer
27k views

Degrees of freedom in a diatomic molecule [duplicate]

We know that a monatomic compound can only have 3 degrees of freedom as we can consider it to be a point mass. However now that we consider a diatomic molecule, there are 3 degrees of freedom in ...
11
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3answers
607 views

What is the microscopic picture for warm air rising?

The usual explanation for warm fluids rising past cooler ones is that the warmer fluid has a lower density. I'm trying to understand what this looks like at a molecular scale. The density seems to ...
9
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2answers
5k views

The distance between touching objects

What is the distance between, say, a cup of coffee and the table it rests on? What is the distance between two touching hands?
4
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4answers
3k views

Is the molecule of hot water heavier than that of cold water?

We know that the molecule of hot water($H_2O$) has more energy than that of cold water (temperature = energy) and according to Einstein relation $E=mc^2$ ,this extra energy of the hot molecule has a ...
3
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3answers
366 views

Creasing of a material at the molecular level

What exactly happens when a material (particularly paper or even cloth or a metal) is folded to form a crease? Why is it that a creased material tends to retain form, while a lightly folded one, '...
3
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1answer
162 views

Experiment to find structure of water

Who first determined the structure of water (two hydrogen atoms stuck to an oxygen atom at approx 105 degrees), and, more importantly, how was this done?
2
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1answer
163 views

Energy levels in molecules

I apologize in advance if this turns out to be a duplicate question. As far as I can understand, if you bring two or more atoms together their wave functions begin to interfere and, since there ...
1
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2answers
750 views

How do atoms in a solid “communicate” force to each other?

What is the mechanism that carries and communicates force in a solid, on the atomic level? Is there some other mechanism besides atomic deformation and proximity? That is, if I had an infinitely ...
1
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1answer
24k views

What's the size of carbon dioxide? [closed]

My question is very simple. How big is a carbon dioxide ($\mathrm{CO}_2$) molecule, i.e. the width, length and height of it?
7
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2answers
835 views

Classical theory fails to explain quantization of motions?

I understand everything written here. But the last point, I cannot get, at all. How does it point towards Quantization of the two motions, since the energy change is not sudden, but gradual? And if ...
21
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3answers
3k views

Why isn't the color of a molecule a combination of the colors of its component atoms?

I was watching a documentary on youtube regarding Quantum Physics when it introduced the wavelengths of light emitted. Did a bit more research over the internet and I believe I understand the gist of ...
8
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1answer
283 views

Are Born-Oppenheimer energies analytic functions of nuclear positions?

I am looking for references to bibliography that explores the smoothness and analyticity of eigenvalues and eigenfunctions (and matrix elements in general) of a hamiltonian that depends on some ...
5
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3answers
3k views

Extra vibrational mode in linear molecule

When calculating the number of vibrational modes for a molecule, the formulas differ for linear $(n = 3N - 5)$ and non-linear $(n = 3N - 6)$ molecules, where $n$ is number of modes and $N$ is number ...
8
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1answer
14k views

Why does a breeze of wind make us feel cooler? [duplicate]

In my Astronomy class, I learned that temperature results from the speed of air molecules colliding into your skin. Thus, if the air molecules in the room have a high kinetic energy and thus collide ...
18
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6answers
3k views

Hot water freezing faster than cold water

This question has puzzled me for a long time. There is already a question like this on Physics.SE. John's answer to the question seems quite satisfying. But when I googled the cause I found this and ...
16
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3answers
11k views

Why is the bottom part of a candle flame blue?

What’s the explanation behind the bottom part of a candle flame being blue? I googled hard in vain. I read this. I don’t understand how it’s explained by the emission of excited molecular radicals in ...
14
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2answers
608 views

Implications of parity violation for molecular biology

In biology, the concept of parity emerges in the context of chiral molecules, where two molecules exist with the same structure but opposite parity. Interestingly, one enantiomer often strongly ...
6
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3answers
1k views

Is photon emission possible without electrons changing energy levels?

Does molecular vibrational transition and consequent emission of infrared radiation involve electrons changing energy level? In wikipedia, about vibronic transitions it says "Most processes leading to ...
4
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2answers
811 views

Is molecular vibration just phonon modes for a single molecule?

I'm reading about Raman Scattering, of which a big part is measuring the energy lost to/gained from Molecular Vibrations. I wasn't totally clear on exactly what is "vibrating" in vibrational modes (is ...
2
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5answers
1k views

What laws (formulas) govern forces between atoms?

What laws (formulas) govern the fundamental forces of nature? For example, gravity is governed by the inverse-square law. I am thinking about how particles attract each other, but also repel. All ...
3
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1answer
7k views

How fast do molecules move in objects?

I guess it depends on the heat or the type of the material but can you give some examples or formulas to calculate it ? The best example would be the average speed of the air molecules (all types in ...
3
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1answer
31k views

Finding the approximate distance between molecules in a gas

I have a problem to understand why the below derivation can be used to find the distance between molecules: This example is an approximation. We are supposed to find the average distance between the ...
3
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1answer
170 views

Relative weights in rotational bands of symmetric diatomic molecules

In an old paper, Ehrenfest 1931, the introduction starts off as follows: The band spectra of symmetric diatomic molecules show certain striking differences from those of asymmetric molecules. For ...
2
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4answers
133 views

Is there a way to “hold a molecule still”?

Is there a way (even if only theoretical) to hold all the nuclei of one single molecule in place, stoping them from vibrating and stoping the molecule completely (0 kinetic energy)? If so, what ...
0
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2answers
1k views

If a water molecule is neutral, how do water molecules attract one another by electric force and form water?

If a water molecule is neutral, how do water molecules attract one another by electric force and form water? This makes no sense to me (I'm new to physics) and my textbook didn't explain this well.
-1
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1answer
39 views

Newtons laws of motion. Tension force

What is the difference between tension and the force that we apply externally. Also when we apply force externally let's say on moleculeA ( connected to other molecules through springs) then by newton ...
8
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2answers
236 views

Is the molecular term ${}^1\Sigma^-$ possible in a molecule?

The old question How to understand this symmetry in the wavefunctions of a diatomic molecule? explores how it is possible for a quantum state to have zero angular momentum about a given axis (giving ...
5
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2answers
2k views

What's the difference between two Hydrogen atoms?

If we are given two Hydrogen atoms, would the only difference between them would be their quantum state (Energy level or eigen value, and the corresponding Orbital or eigen state) and their location (...
3
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3answers
961 views

How do the molecules of reacting compounds proceed to form “Most Stable” molecule?

This question is a cross post from chemistry. I'm not very convinced with the answer there. So, I'm posting it here. I'm tutoring few students for Chemistry. During the course, I many times use the ...
3
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2answers
150 views

During the “Dark Ages” of the Universe's evolution, how lumpy (anisotropic) and dynamic was the mass distribution?

In the dark ages between recombination (~0.4 Myr post-BB) and reionization (~300 Myr post-BB) of atoms, there was not any condensed-phase matter (except maybe some form of dark matter), nor radiation ...
2
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2answers
821 views

Actual Degree of Freedom of Diatomic Molecule

Ok, I have 2 very different values for degree of freedom(DOF) of diatomic molecules arising due to the difference in the vibrational DOF of the diatomic molecules. According to this DOF wiki page:- ...
2
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1answer
114 views

Has any scientist actually seen a $H_2O$ molecule vibrate?

Has any scientist experimentally confirmed that H2O molecules vibrate when heat energy is provided to them? Maybe by passing X-Rays through them or by some special camera...?
1
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2answers
9k views

How are bond angles determined?

Electron microscopes cannot clearly depict the exact shape and structure of atoms and molecules, even though it does show a vague, cloudy image. In my AP chemistry class, I learned that the bond angle ...
1
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1answer
3k views

Degrees of Freedom of a Linear Triatomic Molecule

I was introduced to a formula for finding the DOF of a molecule which was 3N-k and i was told, it was just for translation and rotational degree of freedom. Here N is the no. Of atoms in that ...
1
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1answer
560 views

2 Extra Degree of Freedom in Linear Triatomic Molecules?

Ok, there is a bit problem in understanding Degree of Freedom of Linear Molecules specially of Triatomic Linear Molecules. See, the DOF in general is given as $f=3N-k$. Here, N=Number of atoms in a ...
1
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1answer
148 views

Which is the same between two connected rooms, relative or absolute humidity?

Question: Consider two glass bottles filled with humid air, connected with a tube. One of the glasses is hot (heated), the other is cold (cooled) and the situation is steady state. How will humidity ...
1
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2answers
89 views

What does this notation mean: $\mathrm{O}_{2} \ \ a\,{}^{1} Δ_{g} ← X\,{}^{3}Σ^{-}_{g} $?

The notation (which I found in the abstract of this paper) is $$\mathrm{O}_{2} \ \ a\,{}^{1} Δ_{g} ← X\,{}^{3}Σ^{-}_{g}. $$ Any help with this? I understand it's talking about quantum states of ...
1
vote
1answer
228 views

If translational energy is a continuum, why molecules don't absorb any energy quantity?

I am just starting with quantum mechanics. Here an image where I show possible transitions but only should excite translational movement. Can a molecule absob ANY quantity of energy if it goes to ...