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Questions tagged [molecules]

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Why don't disturbances/wind move at the speed of sound in air?

Why don't sound waves move at the same speed as air that has a pressure differential? Imagine you have a box that is filled with air. One half high pressure air, the other half low pressure. They are ...
Wyatt's user avatar
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4 votes
3 answers
508 views

Why potential energy is not considered in the internal energy of diatomic molecules?

In thermodynamics, I am taught that there are 5 degrees of freedom in diatomic molecules since there are 3 for translational and 2 for rotational. I interpret degrees of freedom as "ways you can ...
bluesky's user avatar
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1 vote
0 answers
18 views

Is there a representation-agnostic way to show that the dynamical vibronic couplings diverge for degenerate potential energy surfaces?

To describe a molecular system beyond the Born-Oppenheimer approximation, the derivation of the vibronic couplings between adiabatic electronic states leads to the conclusion that couplings through ...
GeoArt's user avatar
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2 votes
0 answers
31 views

Could the scattering of molecules lead to bond compression?

Suppose you were to send a fast moving binary molecule (such as H-H) at another large target atom A such that the molecule is aligned with the direction of its travel towards the target atom. In other ...
EigenDragon16's user avatar
-1 votes
1 answer
57 views

Why does an atom become positively charged when it shares its lone pair?

Why does an atom become positively charged when it shares its lone pair? In NH3, Nitrogen doesn't get positive charge when forming covalent bond with Hydrogens. But why does it get positive charge ...
Akhilesh G's user avatar
4 votes
3 answers
216 views

How large are atomic positional/angular fluctuations within a molecule?

I have seen videos of thermal fluctuations/oscillations of atoms that have covalent bonds with each other, and they are usually quite dramatic. I'm curious how strong the fluctuations really are of a ...
user56834's user avatar
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3 votes
1 answer
65 views

How does the united-atom description work? [closed]

I'd like to know something regarding the united-atom approximation: Consider a homonuclear diatomic molecule e.g. $\mathrm{N}_2$. One can obtain its "equivalent" atom that has a nucleus of ...
Eduardo Kuri's user avatar
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0 answers
19 views

How to determine refelection symmetry of molecular term in relativistic (spin-orbit) molecular term?

It is quite clear and well-described how to determine the molecular term of diatomic molecule from interacting atoms (including parity and reflection symmetry): https://chem.libretexts.org/Bookshelves/...
Adam 's user avatar
3 votes
1 answer
103 views

Pauli exclusion principle and van der Waals force

On the Wikipedia article on van der Waals force, one of the contributions to intermolecular forces is A repulsive component resulting from the Pauli exclusion principle that prevents close contact of ...
Machine's user avatar
  • 1,995
1 vote
1 answer
39 views

Atomic force is weaker than nuclear force? A terminology question

I'm reading Megawatts and Megatons and on page 15 came across a statement I don't recognize: The nuclear force acting on a single proton is approximately what is needed to support a mass of a hundred ...
Maury Markowitz's user avatar
2 votes
0 answers
83 views

Why does $\rm{H_2 O}$ have 12 degrees of freedom?

I know there will be 3 translational D.O.F. and 3 rotational D.O.F., and it can have 4 vibrational D.O.F. (one potential and one kinetic) for each O-H Bond. But from where does 2 more D.O.F. come from?...
Ujjwal's user avatar
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7 votes
3 answers
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Will a piece of coal burn at the atomic level at room temperature?

If there is a piece of coal in the open air at room temperature, some of the molecules in the surrounding air will have sufficient velocity to oxidize the carbon in the coal. Will the surface of the ...
Belu boy's user avatar
2 votes
2 answers
380 views

Dielectric and dipole

When a molecule of a dielectric material is placed in an electric field, the molecule acquires an electric dipole moment. Why?
Sam Tunkaho's user avatar
21 votes
9 answers
5k views

Is there such a thing as a "physical" fractal?

The recent discovery of a molecule that mimics the Sierpinski gasket has spurred headlines identifying it as the first fractal scientists have found in nature. I find these claims highly dubious ...
starseed_trooper's user avatar
0 votes
1 answer
65 views

How fast does information travel through air molecules?

You're always told that information travels through air (speed of sound) at appx. 767 mph. This doesn't tell you how fast the transfer of momentum happens between the actual molecules of air. So how ...
Wyatt's user avatar
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0 answers
14 views

Conflicts on spin directions in the molecular term symbol for O$_2$

We know that the ground-state electron configuration of O$_2$ is $K K (\sigma_g 2s)^2 (\sigma_u 2s)^2 (\sigma_g 2p_z)^2 (\pi_u 2p_x)^2 (\pi_u 2p_y)^2 (\pi_g 2p_x)^1 (\pi_g 2p_y)^1$. The spins of the ...
ranger's user avatar
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1 vote
0 answers
25 views

Definition of molecular vibrational coordinates

The wavefunction of a molecule is a function $f(x_1,\ldots,x_N)$ taking the coordinates of the $N$ atoms in the molecules (we ignore the electronic motion) and returning a complex number. ...
creillyucla's user avatar
2 votes
2 answers
74 views

Can latent heat exist when both phases cannot exist at same temperature?

This is my understanding (please tell me if i am going wrong anywhere): During phase change (i.e. ice melting into water) the molecules absorb heat, gain more random kinetic energy, and spread apart (...
Varshil MVH Pets's user avatar
0 votes
1 answer
36 views

Symmetry eliminates degrees of freedom

Consider a system of $n$ particles, such as isolated atoms, molecules, nuclei, and the solar system, with $3n$ degrees of freedom; why does translational invariance eliminate three degrees of freedom ...
Xin's user avatar
  • 11
-1 votes
1 answer
29 views

Can molecules bend light?

As we know, objects with a large gravitational field can bend light, but, my question is, Can molecules bend light? Since molecules have a small amount of gravity, couldn't they bend light in at least ...
Kellan Heerdegen's user avatar
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0 answers
41 views

Head-on collision of $\rm N_2$ and $\rm CO_2$ molecules [duplicate]

Consider a standing sound wave formed in the air in conditions close to standard pressure and temperature in the antinode region. On the molecular level, it will involve multiple collisions of air ...
Stan Tarka's user avatar
5 votes
1 answer
61 views

Can a homogeneous chemical solution really not be split by centrifuge?

Assuming I have a homogeneous solution such as salt in water. My intuition tells me that gravity or centrifugal forces would affect sodium ions more than water molecules. Theoretically, if I could ...
tobu's user avatar
  • 51
0 votes
6 answers
149 views

Conservation of water?

I know that water can exist in various states (liquid, solid, ...) and can be in various places (clouds, oceans, ground, ...). What I want to know is whether or not the total number of water ...
Will.Octagon.Gibson's user avatar
0 votes
0 answers
68 views

Carbon dioxide vibration

Can we induce antisymmetric stretching vibration in carbon dioxide molecules by collision with nitrogen molecules in air at standard temperature and pressure?
Stan Tarka's user avatar
-1 votes
1 answer
119 views

Should natural frequency be modeled using molecules?

Consider an object. This can be anything from a metal ball to a table, etc. Now this object has a natural frequency. When we hit the object, it will start vibrating with a certain frequency $f$. ...
Riemann's user avatar
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0 votes
2 answers
47 views

Quantum position in molecular vibration

Evere molecule consists of atoms that vibrate around their equilibrium positions. This can be viewed from a classical or a quantum perspective. However, I found a seeming inconsistency between these ...
Riemann's user avatar
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0 votes
0 answers
30 views

How do you accelerate a molecular structure with EM wave pulses without heating it up?

vibrating the atom good| heat bad|fast-moving vehicle bad| one-meter cube with different atoms trying to accelerate its whole molecular structure with EM wave pulses but not cause heating damage
ElyasThe Cool's user avatar
-3 votes
1 answer
228 views

Why isn’t $\rm H_2 O$ a primordial element? [closed]

We’re told the universe was very hot and energetic immediately after the Big Bang, and just shows H2O was present early on. Yet, it is not considered to be a primordial element. Why is that?, and what ...
Patrick Payne's user avatar
0 votes
0 answers
97 views

How many degrees of freedom does a diatomic and triatomic molecule have at high temperatures?

I understand that a diatomic molecule has 3 translational and 2 rotational degrees of freedom. But since there is only 1 vibrational mode associated with a diatomic molecule and 1 vibrational mode is ...
Srijan Das's user avatar
1 vote
1 answer
67 views

Eigenvectors sign in $\rm NH_3$ Molecule

Let's consider an $\rm NH_3$ molecule. The Hamiltonian in the $\{|\psi_L>,|\psi_R>\}$ basis can be written as: $$\hat{H}=\begin{pmatrix} E_0 & -A \\ -A & E_0 \end{pmatrix}$$ Now by ...
Lucas's user avatar
  • 319
5 votes
2 answers
352 views

Explanation on this Molecular hamiltonian

I have a question regarding an old exam (quantum at undergraduate level) question that I never fully understood. We have a Hamiltonian $$H= E\begin{pmatrix} 0 & 1 & 1\\ 1 & 0 & 1 \\ 1 &...
smiths's user avatar
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0 votes
0 answers
10 views

Is there a formula that can be used to calculate the rate of non-nuclear spallation due to molecule-surface collisions?

Spallation is an overloaded term and most articles discuss other forms of it (such as nuclear spallation or meteor impact) than the type that I would like to learn about. I'm interested in spallation ...
phil1008's user avatar
  • 271
1 vote
0 answers
19 views

Antisymmetry of the total molecular wave function in case of orthohydrogen

If my understanding is right, the total wave function of any system containing electrons and protons (and any other fermions for that matter) must be antisymmetric under exchange of the respective ...
QuantumQuasar's user avatar
3 votes
1 answer
92 views

Pauli exclusion principle in case of the $H_2$ molecule

Why do electrons in an $H_2$ molecule have opposite spins, while protons do not necessarily exhibit this behavior? Considering that both are fermions, shouldn't they both adhere to the Pauli exclusion ...
QuantumQuasar's user avatar
7 votes
5 answers
784 views

Why do molecules lack the inversion symmetry of the full molecular Hamiltonian?

The nonrelativistic molecular Hamiltonian has inversion symmetry, since the kinetic energy operator and the Coulomb operator have inversion symmetry, $$\begin{aligned} \hat p_i^2&\stackrel{i}{\...
Hans Wurst's user avatar
  • 1,564
2 votes
1 answer
110 views

How do you calculate the air friction on a large magnetically levitated ring travelling within a toroidally shaped vacuum enclosure?

For this question, assume... That the inner wall of the enclosure and the surface of the ring are smooth. A high vacuum level, but not a perfect vacuum. Rarified gas density is $\rho$. That the ...
phil1008's user avatar
  • 271
8 votes
4 answers
5k views

Since water is a molecule, can the aerosol sprayed through double slit form interference pattern?

A water molecule is made of 1 oxygen atom and 2 hydrogen atoms, so it is very small, like quantum scale small. So if I accelerate a bunch of these water molecules through the double slit using a spray ...
user6760's user avatar
  • 13k
0 votes
0 answers
41 views

How many degrees of freedom does the water molecule have? [duplicate]

This is mainly a question about molar heat capacity. I've read many different values for the degrees of freedom of water, for example f = 12 on (https://en.wikipedia.org/wiki/Molar_heat_capacity). But ...
Zedssad's user avatar
  • 73
1 vote
2 answers
100 views

How is energy conserved in formation of chemical bonds?

I understand that when an H$_2$O molecule is formed, it has lesser total energy than the constituent (2H and O) atoms. I also understand that the potential energy (PE) will be reduced when the atoms ...
Alex's user avatar
  • 79
3 votes
1 answer
167 views

Molecular orbital notation

I'm reading about papers about atom-ion interaction. There are some states as showned above. The notations of the states look like molecular orbital since $\Sigma$ and $\Pi$ is usually used in orbital ...
Han Bao's user avatar
  • 33
1 vote
0 answers
77 views

What exactly are the categories of intermolecular forces

So I read the wikipedia and its catagorization is somewhat vague. (Link here: https://en.wikipedia.org/wiki/Intermolecular_force) In wikipedia, the van der waals forces are quite clearly stated to ...
aaa's user avatar
  • 11
0 votes
1 answer
73 views

Do the molecules inside a dielectric physically move when the dielectric is polarized by an external electric field?

Today a colleague and I had a heated debate over whether, when an external electric field is applied across a dielectric, the molecules in the dielectric actually move/rotate (flip to align with the ...
user9413641's user avatar
1 vote
0 answers
42 views

Electric dipole vs density gradient

Chemist here, so please excuse me for asking trivial stuff. I am trying to represent the electron density of a molecule as a bunch of point charges. One program that I use can calculate electron ...
andrew.shyichuk's user avatar
0 votes
0 answers
16 views

Generalized Lotka–Volterra equations to explore filling of energy levels in mixtures of interacting diatomic molecules

Did anyone saw any application of Generalized Lotka–Volterra equations to explore filling of energy levels in mixture of interacting diatomic molecules. The idea is to consider molecular interaction ...
Vadim Astakhov's user avatar
0 votes
0 answers
28 views

Double nomenclature of molecular orbitals

I'm studying molecules from Brandsen-Joachain's book: "Physics of atoms and molecules". In chapter 9 he talks about molecular orbitals, and then he specifically talks about them for ...
Rhino's user avatar
  • 693
1 vote
2 answers
99 views

Is many-electron system's energy bounded from above?

A many-electron system with molecular Hamiltonian under the Born-Oppenheimer approximation has a finite ground state energy, which means its eigenenergy is bounded from below. In my research, I need ...
Andy Liu's user avatar
0 votes
1 answer
298 views

Symmetry of the hydrogen molecule wave function

Due to their overlapping wave functions, electrons in an $H_2$ molecule must posses opposite spins. The nuclei (two protons) on the other hand are far enough apart for the Pauli exclusion principle to ...
QuantumQuasar's user avatar
0 votes
1 answer
41 views

Derivation of particle distribution in a gravitational field

I'm trying to figure out where my logic is failing in the derivation of the concentation of particles with respect to the height in constant temperature and gravity ($n(h)$). So we have the following ...
Krum Kutsarov's user avatar
2 votes
0 answers
59 views

On completeness of a set of commuting operators for homonuclear diatomic molecules

The electronic Hamiltonian for a homonuclear diatomic molecule is $$\hat{H}=-\sum_{i=1}^N \frac{\hbar^2}{2m} \nabla^2_i -\sum_{i=1}^N \frac{Z_Ae^2}{4\pi\epsilon_0|\vec{r}_i-\vec{R}_A|} -\sum_{i=1}^N \...
Simone's user avatar
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1 vote
0 answers
9 views

What is the state of the art in nanophotonic biosensing?

Over a decade ago I've been doing research in nanophotonic biosensing and all the reviews from those times were very impressive. Some plasmonic structures were capable of single-molecule detection and ...
user46147's user avatar
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