Questions tagged [molecules]

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943 views

Does gravity have anything to do with Van Der Waal's forces?

Does gravity have anything to do with Van Der Waal's forces? Just throwing this out there, I was wondering if they do because gravity is such a weak force and the VdW forces at a molecular level could ...
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3answers
8k views

Is it possible to obtain antiwater from antihydrogen and antioxygen atoms? And how is its property w.r.t. the ordinary water?

I am interested in experimental physics and looking for information about the above question.
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1answer
151 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 ...
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0answers
33 views

Determination of electromagnetic wave absorption by molecular vibration mode

In this physics.stackexchange answer, it is stated that the absorption of electromagnetic wave at a given wavelength by a molecule is determined by its vibration modes. What is the exact equation/...
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40 views

Partition Function for Molecules

I want to calculate the heat capacity for molecules in thermodynamics by using the partition function. I have given the Hamiltonian $ H = \frac{p_x^{2} + p_y^{2} + p_z^{2}}{4m } + \frac{p_\theta^{2}}{...
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1answer
2k views

Negative or positive binding energy?

I'm working with modern physics atm, and can't seem to wrap my head around the binding energies of some molecules. At first, I thought that a negative binding energy = unstable molecule, and a ...
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1answer
120 views

Explanation of rotational barrier in molecular physics

I remember that in my molecular physics lecture, I learned that rotating molecules have to pass a rotational barrier before they can dissociate, in contrast to only vibrating ones. Could someone give ...
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1answer
1k views

Notation for electronic states of molecules

I came across a question using a notation for electronic states of molecules that I do not understand. The question talks about electrons in molecules of $^{27}$AlH getting excited to $A^1\Pi $ ...
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2answers
68 views

Compression limits

As we have elastic and plastic deformation within objects when we apply stress to an object is there a similar process for compression. Is there a limit where we compress something where it will not ...
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1answer
131 views

Why is there no Sigma-minus ground state for molecular hydrogen ion?

I'm studying a bit of molecular physics and having some trouble understanding the +/- symmetry in a simplest molecule like a molecular hydrogen ion (2 protons and 1 electron). In a book, usually they ...
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1answer
2k views

Collisions of gas molecules with walls of a container [closed]

I am to calculate the rate of collision of gas molecules with the walls of a container with dimensions $3m\times4m\times2m$ at room temperature (20°C) and pressure 1atm. For reasons of simplicity I ...
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1answer
2k views

What is the difference between a rigid diatomic molecule and non-rigid diatomic molecule?

I started a mock paper for one of my entrance exams with this fairly easy question. I rearranged the equation and got 5/2, knowing that a diatomic molecule has a Cv of 5/2, i concluded that the answer ...
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2answers
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Does hot air have high pressure, and does compreesed air have high pressure?

I have hear a lot about high pressure. Sometimes it says that warm air is less dense and has low pressure, but I thought warm air has high pressure. I know that compressed air is going to be hot, so ...
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2answers
154 views

Van der Waals forces & Partial charges

We're told that charge is quantized. That the charge any body carries has to be an integral multiple of the fundamental unit of charge: $e=1.602×10^{-19}C$ such that $q=ne$ where $n$ is an integer. ...
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5answers
8k views

Is it heat that causes vibrations on particles or is it the vibrations that causes the heat?

I was taught that molecules move more random when its hot. I am just wondering what really is it that causes something to heat up.
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0answers
181 views

Activation energy of vibrational modes in diatomic gases

My question is related to the calculation of the heat capacity of diatomic molecules. It is easy two see that such atoms have a Hamiltonian $$ H=\frac{P_x^2+P_y^2+P_z^2}{2M}+\frac{L^2}{2I}+\frac{p_r^2}...
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1answer
8k views

Why does water have 9 degrees of freedom and that too all vibrational?

How does water has 9 degrees of freedom? If it can vibrate about all three atoms then why can't a diatomic molecule also have 2 instead of 1 possible vibrations? I haven't studied quantum mechanics ...
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3answers
128 views

Does atmospheric $CO_2$ heat up when or while or after it reradiates IR back towards Earth?

I get that $CO_2$ absorbs radiation at a frequency that is associated with the energy levels of atoms bumping around and the molecule rotating, and by electrons. 1) Maybe that is not thermal energy, ...
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2answers
459 views

Does the $p^+p^-e^-$ system have bound states?

This is batted a bit off the wall, so bear with me. The hydrogen molecular ion, $\mathrm{H}_2^+$, is the simplest three-body system in molecular physics, and in the Born-Oppenheimer approximation its ...
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0answers
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What happens to the air inside a dry leyden jar?

Or between two similarly charged plates? If I negatively charge two plates and push them against each other until I can feel the repulsion (I don't actually have the workbench to do this) do the air ...
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1answer
662 views

LCAO - Constructing a molecular wavefunction

I am a theoretical physics student and have been studying the LCAO (Linear Combination of Atomic Orbitals) technique from the perspective of a physicist. I would like to get some explicit ...
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0answers
573 views

mass difference between inhaled and exhaled breath [closed]

I was recently asked the following question When breathing, approximately 5 percent of each exhaled breath is carbon dioxide. Neglecting any difference in water-vapour content, estimate the typical ...
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1answer
1k views

Resonance integral in LCAO method for homonuclear biatomic molecules

In LCAO method for approximate solutions to Shrodinger equation of homonuclear biatomic molecules, it is defined an integral called "resonance integral" whose expression is: $$ \beta = \langle\Psi_{a}|...
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2answers
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What *really* happens to atoms in chemical reactions?

I am imagining that the occasional oxygen might be floating close enough to a certain calcium atom and take the two electrons, which will ionize them and they will now 'glue'. Maybe the same thing ...
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2answers
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Can we create something like a temperal invisibilty cloak by phasing molecules? [closed]

I am only just 14 years old and i am interested in this subject. Can you pls help me with it.thank you.
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1answer
57 views

water molecular structure [duplicate]

If someone claim that chemical formulation for the water isn't $H_2O$, how we can prove for he/she that water has constituted of $H_2O$ molecules. Generally based on what evidences we sure that water ...
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2answers
553 views

In a real gas is heat carried by molecular vibrations as well as translational velocity?

It's clear that the mean velocity of gas particles determine what we measure as temperature, but is there also a significant amount of energy carried in molecular vibrations? For example, at the same ...
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101 views

What are the restrictions on the azimuthal quantum number $\ell$ for $\sigma$ transitions?

I know that $\pi$ transitions only allow $\Delta \ell = 1$, but what about $\sigma$ transitions? How are they restricted?
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2answers
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Why the intermolecular force can be attractive and repulsive?

As we all known, the fundamental force between objects (such as Gravitation Force, Coulomb Force) can be either attractive or repulsive. But I am curious about the intermolecular force $$ f = \...
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1answer
277 views

Number of degrees of freedom for the 2D diatomic molecule

How many degrees of freedom does a diatomic molecule has in two dimension?
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1answer
40 views

Do H$_2$ fuel cells function the same as H?

Are the 2 hydrogen molecule broken apart first? or does the $H_2$ directly react with the dialetric/anode/cathode to produce electricity? i.e. http://www.fuelcellstore.com/horizon-aerostak-a200
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2answers
617 views

Mathematical statement of the Born-Oppenheimer approximation

I have been looking up a formal mathematical definition of the Born-Oppenheimer approximation. I have thus far come across two (my wording): Definition 1 The Born-Oppenheimer approximation is ...
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1answer
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Finding the average kinetic energy of the molecules using thermodynamics [closed]

I've a simple problem: In a balloon with volume $V=0.05m^3$, there is $0.12 kmol$ gas $\frac{m}{\mu}=0.12kmol$, under pressure $P=0.6*10^7Pa$. Find the average kinetic energy of the molecules? The ...
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1answer
288 views

How do visualization programs generate electron density meshes?

How do visualization programs such Coot and PyMOL generate electron density meshes? Example of an electron density mesh rendered in PyMOL: Currently, there are no resources on the internet to answer ...
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2answers
593 views

Why is the melting point of a solution lower than one of both of its components?

The melting point of ice (H2O) is at 273K, and one of salt (NaCl) is at 1074K. However, if one dissolves salt in water, the melting point of the solution will be at ~250K. Why is it so low if the ...
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4answers
460 views

How are we stardust?

I am a layperson and certainly not a physics student, though I'm sure that is palpably obvious. I have a strong appreciation for people like Carl Sagan, Lawrence Krauss, and Sean Carrol. I'm often ...
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0answers
937 views

Why are the leaves green? [closed]

My professor mentioned in yesterday's class that the color of the leaves can be explained by evolution, that they adapted to reflect the green color because the sun has its peak right about there: He ...
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3answers
776 views

How do molecules scatter light?

I've read that during Rayleigh Scattering, a photon passes through a molecule and the photon's electric field creates a dipole in the molecules. But what I don't understand is what happens next. How ...
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0answers
80 views

Are the $+\leftrightarrow+$ and $-\leftrightarrow-$ methanol rotational transitions dipole-allowed?

I am quite confused about the origin and justification of the rotational selection rules of methanol, and I would appreciate any help or references. As far as I understand, there are three irreducible ...
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1answer
21 views

can we move molecules in solids or surfaces via applying voltage?

Is it possible to have movement of molecules/atoms in a solid, under electric field? Similar to the movement of electrons under electric potential difference? I was thinking if this can happened to ...
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0answers
40 views

Determining the symmetry operations of an arbitrary molecule

I need to write a code that's determining the symmetry of a molecule, knowing the coordinates of the atoms. Many quantum chemistry codes do that already, but I don't know exactly how. Suppose I want ...
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1answer
465 views

What happens once all electrons in a material are in the excited state?

I think this question would make a bit more sense if we consider an ideal thought experiment. Imagine a molecule, call it Z, with just three electronic states. One molecular orbital has energy ...
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1answer
296 views

How does a fish not live when there is still water in the acquarium? [closed]

Can an acquarium still contain water but no oxygen (which seems impossible since water exists means oxygen exists!) for the fish to live on?
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1answer
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Potential Energy of two atoms in diatomic molecule [closed]

The potential energy of two atoms in a diatomic molecule is approximated by $U(r)=a/r^{12}−b/r^6$, where r is the spacing between atoms and a and b are positive constants. a) Find the force $F(r)$...
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2answers
483 views

Two electrons Gaussian Integrals

I want to implement a Hartree-Fock C++ program for my blog. I found on 'Mathematica Journal' a set of three papers that describe the evaluation of Gaussian molecular integrals. The problem is that ...
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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 ...
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1answer
371 views

Molecular Orbitals and Nodal Symmetry

I am currently doing a solid state physics class and am stuck on a concept regarding molecular orbital (MO) hybridization. As an example consider an HF molecule bonded along the z-axis. This molecule ...
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2answers
407 views

Dipole interaction for a two-level system in a trap potential

Consider a two-level system under the following Hamiltonian: $H=H_{I}+H_{E}+H_{dip}$ where $H_I$ is the Hamiltonian for the two internal states of the two-level system $span \{\left |e \right> {,}...
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1answer
104 views

Could Absolute Zero Stop an Electron Beam? [closed]

Context: Okay, I have a comic book scenario and I want to know what would happen. Fighter A can forcibly control electrons in the state of an electron where it is both particle and wave, and when ...
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3answers
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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 ...

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