Questions tagged [molecules]

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What is the capacitance of ferrodoxin molecule?

On Wikipedia it says that a ferrodoxin molecule is a biological capacitor which transfers electron to change the oxidation state of iron from $\text{Fe(II)}$ to $\text{Fe(III)}$. Now I simply want to ...
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Hilbert space of a diatomic molecule

In molecular quantum mechanics, it is very common to model a diatomic molecule as a two-level harmonic oscillator with vibrational levels lying within the electronic states: In most of the textbooks ...
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What causes the volume of an ideal gas in a container that changes volume (like a balloon)?

As we don't consider molecular volume or any interaction between molecules in an ideal gas, what causes its volume? What is the volume given by PV=nRT? If we take a balloon as an example, what ...
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Why do two molecules of an element attract each other?

I was thinking about molecular attraction and a question suddenly struck in my mind which is 'Why do two molecule of an element attract each other?' The answer is easy when we discuss about compound ...
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If contact forces are repulsive then how are we able to pull stuff? [closed]

I searched a lot on internet(especially physics stackexchange) about the nature of contact forces. I came to know through most of them that it is repulsive in nature which surely means that your hand ...
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Is it possible to approximate the shapes of molecules based on the solutions to the Schrodinger Equation of the Hydrogen Atom?

I understand that the Schrodinger equation of the Hydrogen Atom can be used to figure out the number of electrons that can fit in each shell electron shell, and the number of electrons that can fit in ...
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Electronic vibrational rotational transition of electrons -- for a transition from $\Sigma$ to $\Pi$ how are P and R branches possible?

Suppose we have a diatomic molecule in a $^1\Sigma$ state, and it transitions to an excited $^1\Pi$ state. Note that the total spin of the electrons remains unchanged ($\Delta S=0$) as we can assume ...
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How does the concept of activation energy work for interatomic collisions?

Say we have a Lennard-Jones -esque potential for colliding atoms. Say this potential admits a bound state at a lower energy than the kinetic energy of the colliding atoms. So forming this molecule ...
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How does removing air from a vessel of water create bubbles?

I recently started reading Richard Feynmans 'six easy pieces'. I did physics and chemistry combined in secondary school but that was 3 years ago and thought it would be a nice introduction back into ...
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Are water molecules at the surface closer or farther apart than the molecules inside?

My lecturer says that since the energy of the molecules on the surface is higher (less negative), then at equilibrium there will be less molecules on the surface, hence the molecules on the surface ...
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Is physical energy is invariant under reflection?

I am wondering whether the energy landscape of a physical system (in particular a molecular conformation) can be considered invariant under reflection of the 3D space. My understanding is that some ...
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Rate Dispersion is the distribution of rates on a rate spectrum. What are the quantities physically associated in a Rate Spectrum?

I am working on a project to decipher the "origin of rate dispersion" arriving because of Heterogeneity in our system using correlation function analysis in Python. Rate Dispersion, non-...
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Why is the Ocean Blue? [closed]

I'm writing an article on the physical property that binds Music and Water -- Harmonics. I understand that the blueness of ocean water is due to the three vibrational modes of water (i.e, symmetric, ...
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Why wet surface is slippery?

Does the presence of water molecules create more gaps between 2 rough surfaces so there is less friction or most of the friction are absorbed by the water molecules?
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On non-existence of molecular helium (and or why that's equivalent to bond order zero)

Why does molecular orbital theory (MOT) imply that molecular helium does not exist? All answers I found in the web use following two standard arguments, but I not see why these are sufficient to ...
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Who first modelled water as a tetrahedron?

Who first modelled water as a tetrahedron? In this model the oxygen is at the center and the two hydrogens are at the vertices (I think, or maybe somewhere along the edges?). Source This gives the ...
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Water molecule $\text{H-O-H}$ angle in electrostatic field

An image showing water molecule within a cylinder with positive charge on the inside and negative on the outside. To what extent will the $\text{H-O-H}$ angle adjust itself to the electrostatic force? ...
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Why is ozone $\rm O_3$ in the Earth's upper atmosphere?

If you look at the density table, you will see that ozone has the highest density among other gases, so why is it in the upper layer of the atmosphere, in the picture I schematically drew how the ...
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How do electron acceptors and donors affect molecular geometry?

I'm currently working with two molecules: Ethylene $CH_2CH_2$ and $CH_2CHCH_2$ (whose name I don't know). The question is how does doping them with an electron acceptor/donor affect their geometry? My ...
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Reference request: advanced book on atomic and molecular physics

I am aware of this: Book recommendation for Atomic & Molecular physics The books mentioned up there are good, like Bransdon and Joachin's book on atomic and molecular physics. But I'm looking for ...
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Why surface tension direction cannot be downwards in direction when considered the surface of fluid?

Like in this figure we see that the surface molecules have a net downward force to all of these so should any force which we made along a line on the surface the force be downwards ? Why the surface ...
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Are the forces between liquid molecules attractive or repulsive?

Surface tension is explained by there being attractive forces between molecules as show in the diagram. But shoudn't repelling or pushing forces exist for there to be hydrostatic pressure. How is this ...
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General Method for Calculating Excluded Volume

In section 5.3 of Kardar's Statistical Physics of Particles, the van der Waals equation is given as: $[P+\frac{u_0 \Omega}{2}(\frac{N}{V})^2][V-\frac{N\Omega}{2}]=Nk_BT$ The van der Waals parameters ...
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Why octet atom are stable? And what make atom unstable?

I have search a lot that want make octet atom stable but all I found is that it need to fill the orbit! why . Why it need to fill the orbit. And I also search that why atom which don't have octet are ...
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Partition function of given system

I am given rotational free energy of a diatomic molecule as $$F_{rot}=-NkT ln[\frac{1}{π}(\frac{2πIkT}{\hbar^2})^{\frac{3}{2}}]$$ The question is if I take the partition function from it would it give ...
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Why does infrared spectroscopy require a change in the dipole moment?

An infrared signal is generated due to fluctuations in the permanent dipole moment, but can an infrared signal be induced in a molecule due to a change in the quadrupole moment?
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Why does a higher temperature increase absorption / optical density?

Suppose we have for example a gas of bimolecular iodine. Suppose we shine ultraviolet laser light on it. Then the absorption of ultraviolet increases when we increase the temperature. From what I read ...
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Quantum mechanical model of benzene ring [closed]

The infinite square well scenario can be used to model the $\pi$-electrons of a benzene ring. It can be shown that the eigenfunctions of the ring can be written as $\Psi_{n}(x) = \frac{1}{\sqrt{L}}e^{\...
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Why do two hydrogen atoms bond?

I was wondering (with my limited classical physics knowledge) why two hydrogen atoms tend naturally to a bonding configuration, I mean, given two hydrogen atoms with zero relative velocity between ...
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Why does the hydrogen molecular ion has no bound state except the bonding state?

Using LCAO method, we can determine the ground state of the hydrogen molecular ion. It is the spatially symmetric state given by $$\psi_+=\frac{1}{\sqrt{2}}\left[\psi_{1s}(r_A)+\psi_{1s}(r_B)\right]$$ ...
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Can molecules used in double slit experiments interact with light? [closed]

If a photon hits a molecule while it's in a wave state will it collapse it into a particle?
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Is it possible to make methane visible?

:) It is just a curiosity question. Under the right conditions, I could clearly see a shadow of warm/cold air. But methane won't create any such shadows. Is there any tool/method that I could use to ...
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Is sound a classical mechanic phenomenon or is it a quantum effect?

I am just curious because sound is longitudinal waves, meaning the energy is passed from one particle to another nearby particle and produces a wave that continues on until it reaches our ear as a ...
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Why aren't triplet states in Hydrogen molecule bound by Pauli's principle?

I am learning about the wavefunction of two electrons in a Hydrogen molecule and I came across following spin states: |↑↑⟩ and |↓↓⟩, which form two of the triplet states in the molecule. This confuses ...
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A poorly posed time dependent perturbation benzene type ring question

In my first year masters QM class my professor recently mentioned an example that he said he would either give on an assignment or possibly put on our exam. We have all our assignments now and it hasn'...
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Can Brownian motion explain why white smoke moves around in the air?

Can Brownian motion explain why white smoke (fume) generated by chemical reactions moves around in the air?
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Does vibration in molecules cause meaningful local differences of time dilation in matter?

I learn through confusion, and something about molecular structure still very much confuses me. A vibrating clock will ultimately run slower than your wristwatch, because of, for one, kinematic time ...
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Strength of intermolecular forces as a function of distance

In Introduction to Mechanics by Kleppner and Kolenkow they talk about the tension force of a string and its microscopic origins. They explain how applying a force on a string slightly increases the ...
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How fast can molecular vibrations become under the application of IR radiation?

It is my understanding that IR radiation can be absorbed by molecules when the frequency of the photon matches the natural frequency of the bonds in the molecule which can cause the amplitude and ...
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Molecular dipole moment transition in bra-ket notation

Below is equation for dipole moment transition: $$\langle \Psi_k| p |\Psi_i \rangle = \langle \Phi \chi_{N,k}|p_e+p_N|\Phi \chi_{N,k} \rangle = \langle \chi_{N,k}|\langle\Phi_k|p_e|\Phi_i\rangle |\...
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Why do we write wave function for electronic transition in molecules like this?

Why do we write transition between two different electronic states like that: $$\bar p_{if}=\langle \psi_i|\bar p|\psi_f \rangle$$ And not like that: $$\bar p_{if}=\langle \psi_f|\bar p|\psi_i \rangle$...
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Bimolecular recombination: How can it be non-radiative for $e$-$p$ pair?

I have understood that the bimolecular recombination of electrons and holes can be radiative when they meet each other, However, I also heard that there are defect sites that can accept electrons and ...
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What is the difference between saturated and unsaturated photoassociation?

I was reading two papers and I came across saturated and unsaturated photoassociation. These papers are DOI: 10.1103/PhysRevA.66.063406 and DOI: 10.1103/RevModPhys.78.483. I am not an expert in laser ...
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Why are molecular orbitals HOMO and LUMO invariant under spin flip?

Atomic theory says singlet and triplet energies for the same orbital differ because of exchange interaction. However, molecular orbital (MO) theory describes the energy between the HOMO (highest ...
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Can you electrically polarize gas?

If you put a non-polar gas like $\rm CO_2$ in a positive electric field, Will it get polarized? What will be the force the molecules get as its attracted to the positive field?
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How does an external electric field induce a symmetry lowering perturbation to the $D_{3h}$ point group?

I have the following homework style question which I will typeset 'word for word'. I am having trouble understanding the authors' solution to part $\mathrm{ii}.$ of the following questions: An ...
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How does the particle's total energy affect the interference pattern? Individual Particle Double Slit Experiment

Double slit experiment with individual particles has been performed with a variety of particles from photons to molecules of up to 2000 atoms. For photons, as the frequency increases (i.e. wavelength ...
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Precise theoretical energy of the dihydrogen molecule as a function of internuclear distance?

I am currently looking for the most state-of-the-art theoretical prevision of the energy of the dihydrogen molecule as a function of internuclear distance as a means of comparison with numerical ...
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Molecular accelerators

I wanted to know if we have accelerators for molecules just like particle accelerators. If so, what are they called and what is the maximum size of the molecules that can be accelerated in such ...
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2 answers
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Why isn't the molecule of water linear straight?

When you see models of water you see something like this: The hydrogens in the water molecule become negatively charged because the oxygen pulls electrons more. So why don't they repel and move to ...
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