Questions tagged [molecules]

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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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21 views

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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3answers
145 views

Do proteins interact through classical or quantum mechanics?

For the protein interactions that occur in our cells, do they "follow" classical mechanics or quantum mechanics when interacting? I have zero knowledge about quantum mechanics, but I was wondering ...
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42 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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4answers
89 views

Is the oxygen molecule $O_2$ fermion or boson?

I ask something makes me confused. In generating singlet oxygen molecule, I initially thought a light (photon) can excite the ground state oxygen molecule. However, my colleague said that process is ...
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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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44 views

Can we hold atomic hydrogen for a long time? [closed]

If we take atomic hydrogen with similar spin together, can we hold it in balloon? I know, that the atom is hydrogen is reactive. But when all atoms will have similar spin, reactions between them will ...
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2answers
65 views

How do you define volume for gases? [closed]

Straight forward question. If atoms forming a gas float far from each other, how can we assign a volume to it? if it is in a container, perhaps we'd say the atoms, or molecules, reach every corner and ...
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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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10 views

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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12 views

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
51 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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2answers
56 views

How do molecules gain kinetic energy from light?

I know that molecules can absorb light through electronic and vibrational excitations, which certainly increase the internal energy of a molecule. This idea is always connected to the quantum theory ...
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1answer
34 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 ...
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0answers
20 views

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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10 views

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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1answer
41 views

Are individual atoms inside a molecule (covalent) still really EM neutral?

I am not asking about ionic bonds. I am in this case asking about covalent bonds. I have read this question: Why do atoms repel when closer but attract when farther apart? Where Swike says: ...
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1answer
34 views

How sound absorption results in heat?

When sound passes through a medium (say, air) and hits the boundary atoms/molecules of another medium (say, a solid) ...... How would you continue the story ? What happens at the interface in cases ...
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1answer
26 views

How will a polar molecule affect another molecule nearby, why it feels a relatively large force?

Mean position of the negative charges and positive changes are not at the same point (polar molecule) how will that affect another molecule nearby, why it feels a relatively large force? Will the type ...
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42 views

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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68 views

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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1answer
47 views

Is the sun required for evaporation?

I understand that the sun would heat up a pool of water causing the overall temperature to increase. This would also mean that more molecules would have enough energy to escape the pool, but wouldn't ...
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6answers
13k views

How is water heavier than petrol, even though its molecular weight is less than petrol?

Molecular weight of petrol is so much higher than water, but when it comes to physical property, weight, one litre of water weighs more than one litre of petrol. How is it possible?
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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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1answer
49 views

Vibrations in Stones and Crystals [closed]

I have read studies done that indicate certain sounds can either disrupt or reinforce the molecular structure (I think this is the terminology used) of living organisms. This is based on the idea that ...
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38 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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55 views

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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1answer
24 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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2answers
81 views

Why is gaseous carbon dioxide transparent? [closed]

Some carbon-heavy products of combustion, e.g. soot, are black, as is carbon in other forms, e.g. graphite. This seems to suggest that carbon is black. But then how can $\text{CO}$ (carbon monoxide) ...
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21 views

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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1answer
48 views

When a diatomic ion dissociates, how does the electron density on each atom change?

Let's say, we have a fluorine molecule (F2), and we take 3 electrons from it, so now its bond starts to stretch, and at last the bond breaks and the two atoms are farther and farther away from one ...
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1answer
77 views

How many degrees of freedom for $\rm N_2O_2$?

From my reading, I have understood examples a diatomic molecule to be $\rm N_2$ or $\rm O_2$, however, the below seems to suggest that $\rm N_2O_2$ is also diatomic. Is this correct and can someone ...
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1answer
62 views

Selection rules in rotational spectroscopy- water molecule

The University of Liverpool maintains a ChemTube 3D page, where it says http://www.chemtube3d.com/spectrorotcd0-CE-TEST-ROTATE-ALL.html *> Highly symmetric polyatomic molecules, such as carbon ...
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14 views

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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161 views

If one divides the molecular dipole of HCl by the interatomic separation, the result is not a multiple of the electron charge. Why is that?

I'm having some trouble understanding the reasoning behind the final note in the following worked problem: An HCl molecule has a dipole moment of $3.4\times10^{-30}\:\rm C\:m$. Assuming that equal ...
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1answer
69 views

Why hot molecules have higher velocities

I'm looking for a something different than the "T is average KE, heat is energy, so adding heat increases the KE and therefore T" explanation. Let's call that the "thermo" side of the argument, which ...
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1answer
42 views

Bouyancy of ozone gas

If ozone is $O_3$ why is it an outer layer of the atmosphere? It seems $O_3$ would sink in a solution of $O_2$, rather than float on it.
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57 views

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\...
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1answer
45 views

Transparency and visibility of light in tyndall effect

Oil and water are both transparent however, they lose their transparency once they are mixed together. What is the reason for this? The size of the molecules are still the same so why does the ...
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Formulae governing the temperature at which molecules can form

This wikipedia page suggests that since stars are incredibly hot, molecules are unstable, and therefore materials exist primarily in their atomic state. Specifically, it states that "... the ...
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2answers
59 views

Degrees of freedom of gas molecules

What is the degrees of freedom of a three dimensional polyatomic molecule when only one vibrational mode is excited?
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68 views

Direction of the permanent dipole moment of the NH$_3$ molecule

What is the direction of dipole moment in a molecule of $\rm NH_3$? Is from hydrogen to nitrogen? Also do we take into account the dipole moment of the lone pair with hydrogen? When we must take into ...
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1answer
53 views

What is quantum molecular movement? [closed]

Q: What is quantum molecular movement? And what are some examples of quantum molecular movement? I’ve been studying a wide arrange of things but one of the top things I don’t understand is quantum ...
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3answers
375 views

Would an $H_2O$ Molecule actually look like this 3D representation if we could see it?

I'm trying to get a much better grasp on atoms and molecules and I am a visual learner. I found the above image here. This intuitively makes sense to me because I can see how the electron orbitals ...
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1answer
45 views

Raman effect and IR absorption

Let's consider a molecule with N atoms, on which is shot a polychromatic IR beam. From the quantum selection rules, we know that in a single event of absorption only one of the 3N-6 oscillators can be ...
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1answer
86 views

What's your favorite textbook on diatomic molecules?

I'm a grad student in AMO physics. I'm looking for another textbook to read on diatomic molecules. Could you please recommend your favorites? I've read 'Spectra of Atoms and Molecules' by Bernath and ...
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1answer
40 views

Interaction between molecules

Does the interaction with enviroment change the geometry of a molecule ? for example in H2O the angle betwen H-O-H is 104.5 degrees. Does this angle change for example if the molecule of water is near ...
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1answer
26 views

Why do low-precision gaskets & seals work?

In lots of applications water or gas-tight seals can easily be formed by tightening two surfaces together. These often consist of crudely made and inexpertly assembled parts, yet they seal so ...
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Is “more added heat, more molecular vibration” an universal property? Or are there exceptions?

Is "more added heat, more molecular vibration" an universal property? Or are there exceptions? Do some substances work the other way around? Or do some other ambient properties modify this property? ...