Questions tagged [molecules]

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How do gaseous molecules arrange themselves in liquids when they are “dissolved”?

To provide some context, I am trying to understand in better detail how oxygen from the lungs passes through a membrane and enters the vasculature in order to be transported via blood. I have ...
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2answers
1k views

Wigner threshold law in photodetachment and photoionization

I am writing this question here because I have a problem in understanding the Wigner Threshold law in Photodetachment and Photoionization. The Wigner Threshold Law is given by: $\sigma$=$E^{L+1/2}$. ...
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319 views

Electron hopping among molecules - Marcus equation

I'm running out of professors to talk to, and I need to clarify a couple of things for the sake of making a realistic model of electron travel through a mesh. This is about calculations of electron ...
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85 views

How did we first discover oxygen exists as $\rm O_2$ and not just $\rm O$?

How did we first discover oxygen exists as $\rm O_2$ and not just $\rm O$ ? (similarly hydrogen as $\rm H_2$ and not $\rm H$) I vaguely remember knowing a story about how the chemical formula of ...
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109 views

If 2 fermionic atoms form a molecule, will the molecule always behave as a boson?

2 fermionic atoms give a bosonic molecule. 2 bosonic atoms form a bosonic molecule. Is there a energy scale where these two molecules will behave differently? If yes, will it depend on the ...
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128 views

How did Lord Rayleigh find the volume fraction of argon to air?

In order to isolate for pure nitrogen, Lord Rayleigh and his colleagues took some air and removed oxygen, carbon dioxide, and water vapour, leaving behind what he believed to be pure nitrogen. In ...
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155 views

Is the translational information all that matters, or do we need to take into account internal states?

For anyone in this community that's familiar with quantum teleportation, I need desperate help. I am currently working on my senior thesis and my goal is to teleport a molecule. Background: So in ...
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1answer
26 views

Binding energy of a molecular ion?

The protons in the $\text{H}_2^{+}$ molecular ion are $0.106 \, \mathrm{nm}$ apart, and the binding energy of $\text{H}_2^{+}$ is $2.65\,\mathrm{eV} .$ What negative charge must be placed halfway ...
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1answer
114 views

How is temperature related to quantum vibrational states of molecules?

When a molecule of greenhouse gas absorbs a photon of long wave infrared radiation it is boosted to the next allowed vibrational state. The vibrational state, as I understand it, involves deformations ...
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0answers
44 views

Existence of an electric/magnetic dipole of a molecule

I have a molecule with a symmetry group $S_3=D_3$. I have to determine if it has a non-zero electric and/or magnetic dipole moment using the representation theory. I'm using the book of Jones "Groups, ...
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4answers
105 views

If I replace water molecules with microscopic solid spheres, will they still reach the same height in communicating vessels?

I'm having an hard time understanding why liquids take the shape of the container or why they reach the same height in communicating vessels. I'm wondering if I try to simulate their behaviour in ...
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174 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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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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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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79 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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136 views

Plasmon quenching vs plasmon decay. What is the difference?

I'm reading an article "Quenching, Plasmonic, and Radiative Decays in Nanogap Emitting Devices" (pubs.acs.org/journal/apchd5). I don't understand the following: Counterintuitively, we evidence ...
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253 views

Why is the activation energy of combustion so large compared with regular bonding?

I wanted to know why combustion requires an activation energy and I found this article (see this too). It says that molecular oxygen ground state is a triplet state (according to Hund's rules), and ...
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383 views

Why is the water diamagnetic?

I checked using my permanent magnet that water is diamagnetic. But why is it like that? Does this have any important consequence for life?
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246 views

Bond Angle in a water molecule

I recently started up reaching up on the Feynman lectures on Physics and in Vol I,Chap 1-2,Feynman states that the bond angle between the hydrogen and oxygen atom is 105° 3′. I know that the bond ...
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196 views

What is a covalent bond?

What is a covalent bond, quantum mechanically? How does it hold the two atoms together, and at one point can you qualify the electron as being shated between two atoms, versus feeling attractive ...
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40 views

Design and construction of a system identifying molecular nitrogen and water

I have read papers that use LIDAR-like and LIDAR-Raman systems that detect elements. I want to measure the vapor water ($\rm H_2O$) and $\rm N_2$ of trees/agriculture using Arduino and low cost ...
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15 views

Transition Dipole Moments and Quantum Yield

I'm using some DFT calculations to compute Transition Dipole Moments between the HOMO and LUMO of a molecule in different geometries. Intuitively, this is closely related to the relative probability (...
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40 views

Incompatibility between the Bohr-Sommerfeld quantization condition and the Dunham expansion

I'm trying to apply the RKR (Rydberg-Klein-Rees) method which computes the classical turning points, $a(E,J)$ and $b(E,J)$ of a diatomic molecule for a rotational-vibrational energy value E, and ...
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37 views

Under what conditions can molecules exist?

I am curious to know the conditions required for any two or more atoms to bond together and form a stable molecule. Is their a set of rules that should be satisfied?
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111 views

Why can we see the fundamental rotational-vibrational transitions of molecules like CO?

In rotational-vibrational spectroscopy, the "fundamental" transition is the one in the lowest electronic state between the first vibrational level ($\nu'=1$) and the ground level ($\nu''=0$). Since ...
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Laser induced Ionization

We know that when a linearly polarised laser field interacts with a diatomic molecule ionization happens when the molecular axis is along the laser-field direction. However, in case of a circularly ...
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2k 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 ...
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157 views

water dipole moment

I'm working my way through Halliday, Resnick, Walker's chapter on electric fields, and there is a solved sample problem (22-5, 8th ed.) about calculating the charge separation on a water molecule. ...
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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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2answers
122 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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39 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
132 views

How to calculate the potential energy of an $H_2$ molecule

From left to right, electron $e_1$, $e_2$ and proton $p_1$, $p_2$. $r_0=0.529nm$ The total energy is sum of energy require to bring each particle to its place. Take the place of $e_1$ is zero ...
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44 views

Why is the potential minimum of a molecule shifted towards greater nucleii separation for excited electron states?

I know it has to do with symmetry of the wave function, but I am having trouble piecing it all together. For a positive H ion we have a symmetric wave function $\psi_{+}$, which base functions $\phi_{...
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707 views

Why and how will the string break?

While i was searching on the identity discussed earlier that is $$1 + 2 + 3 + 4 + 5 + ... = -\frac{1}{12}$$ I found a similar identity applied to physics concept. It started by arranging long ...
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173 views

How large must the Quantum teleportation fidelity have to be in order for it to be useful?

This question relates and stems from my original question. Please read this one and the comments before answering this question. Quantum Teleportation Fidelity I know that for discrete variables ...
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Law of equipartition of energy, shouldn't kinetic energy per molecule by $(3/2)kT/f$

I study that according to the law of equipartition of energy the average kinetic energy associated with each degree of freedom is equal to $(1/2)kT$. But shouldn't it be $\frac{(3/2)kT}{f}$ where $f$ ...
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Vector components for the dipole of water

I was looking online for the components for the dipole moment vector of water in the molecular frame. Does anyone know what the values would be for $\mu_x$, $\mu_y$ and $\mu_z$ for a water molecule in ...
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43 views

What's the most likely mass for ethanol?

I am interested in learning a little about mass defect and calculating the molar mass of ethyl alcohol. I found this table of atomic weights and would like to use it to compute the mass of the ...
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Where does the energy go that is associated with a shift in a FRET spectrum (Forster Resonance Energy Transfer)?

In the commonly used Jablonski energy diagrams, some sort of loss during resonance energy transfer is usually indicated via horizontal lines below the excited state energy of the oscillator (see for ...
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Does emission-spectrum of molecule equal sum of emission-spectrum of its components

Imagine a number of elements with known emission-spectra, that form a primary chemical bond of either * ionic * covalent * metallic type. Does the emission-spectrum of the resulting molecule match the ...
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1answer
52 views

Different energy levels in quantum mechanics

I have a doubt regarding energy levels. I saw that translational energy levels are quasi-continuous, rotational energy levels are discrete and vibrational energy levels are more discrete. I want to ...
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30 views

Average position in the Morse potential

Does anyone know the analytical expression for $\langleψ_n|x|ψ_n\rangle$ in the Morse potential? In other words, I'd like to find the average position of a particle at the $n$-th vibrational level in ...
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Which bonds are broken when we use high laser energy?

If we suppose as in the picture that a laser with high energy been used to break down the bounds, what exactly happens? Is there anything to do with molecular orbitals? or?
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Is there a way to calculate the molecular ionization energy from the single atom ionization energies?

Let us call the ionization energies of three atoms $E_1, E_2 $ and $E_3$. Is there a way to at least approximate the ionization energy of the molecule formed by those three ionization energies?
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Preconditioning self-consistent iteration

Publication arXiv:0804.2583 describes a method for doing self-consistent iteration without having to diagonalize the Hamiltonian operator at every step. IX. PRECONDITIONING As already ...
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Reference for the electronic levels of the nitrogen atoms resulting from the dissociation of the nitrogen molecule

I would like to know a book or paper that makes a detailed description of the electronic levels of the nitrogen atoms, N+N, resulting from the dissociation of the nitrogen molecule, N$_2$, also at a ...
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Do delocalized electrons have different energies?

Consider a molecule with alternating single and double bonds between carbon atoms, such that multiple resonant configurations are possible, e.g. beta-carotene. While using UToko's edx course about ...
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Branch of Physics that Examines Atoms Relationships

Is there a specific branch of physics that can examine and calculate the strengths of atomic or molecular bonds and predict how they are going to break, putting into consideration the surrounding ...
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Why don't asymmetric molecular orbitals and lone pairs in linear molecules lead to an additional degree of rotational freedom?

For example, in CO2, the molecule is linear and thus rotation about the intermolecular axis leads to an identical molecule. But if you consider the pi molecular orbitals, which are radially ...
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Van der waals forces interaction

My slides say: A gas with low density in which you can consider the attractive energy the sum of the isolate atoms couple $$ u=\int^S_\sigma{4\pi\frac{N}{V}}\left(\frac{\beta}{r^6}\right)r^2\...