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Questions tagged [molecules]

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1answer
62 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 ...
0
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1answer
23 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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0answers
12 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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2answers
41 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 ...
1
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1answer
67 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 ...
0
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1answer
35 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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0answers
41 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\...
2
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1answer
37 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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0answers
15 views

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
26 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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0answers
57 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 ...
0
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1answer
48 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 ...
4
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3answers
175 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 ...
0
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1answer
30 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 ...
0
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1answer
47 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 ...
1
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1answer
39 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 ...
0
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1answer
22 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 ...
3
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3answers
65 views

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? ...
0
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2answers
67 views

Degrees of freedom for diatomic molecules [duplicate]

I have a doubt in understanding about the degrees of freedom (dof) ......as I have learned dof is nothing but the necessary parameters to specify the location and configuration of a system.....if that'...
3
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3answers
86 views

How do “pouring spouts” prevent liquid from escaping through the air intake?

You may be familiar with the types of pouring spout found in many professional cocktail bars, similar to the following: The hole on the top of the spout is an air intake, which connects to the narrow ...
2
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1answer
93 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 ...
0
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1answer
39 views

Why is the transition from the $3s$ state to $3p$ state in nitrogen observable in the emission spectrum but not in absorption?

Why can one observe an electronic transition of the $3s$ state to the $3p$ state in the emission spectrum of the nitrogen atom, but not in its absorption spectrum? I know that the selection rules ...
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0answers
11 views

Photoreactivity/photofragmentation dependence on pressure

Most of the photofragmentation studies I see are done in vacuum or lower pressure. Is this just because of the experimental limitations or the photofragmentation doesn't matter the surrounding ...
0
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1answer
57 views

Confusion between molar gas constant and boltzmann constant?

So after reading reading through internet I came to the conclusion that : For gas of any element PV/T = Constant of proportionality and that constant of proportionality can be expressed in ...
2
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2answers
65 views

Would I be able to feel a single-molecule wide string?

Imagine there is a material that is so strong it can form several meters string while being only a single molecule wide. It is securely attached and can withstand any human pressure. What happens if I ...
0
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2answers
136 views

Radiation absorption by $CO_2$ molecule in atmosphere

What kind of radiation (light) does CO2 molecule absorb -UV or IR? I've read that it's infrared however some sources suggest ultraviolet. If so, how might it be possible?
2
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2answers
58 views

How do $H_2$ lamps work?

When a hydrogen ($H_2$) lamp is subject to a high voltage hydrogen atoms release energy in the form of light. Somehow $H_2$ is splitted. But... Why high voltage produce the dissociation? Does ...
0
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1answer
100 views

Scientific explanation for smell? [closed]

This might be more on the philosophical side. We already know a lot about light. How it is generated and how it interacts with a material. Phenomenon such as Interference, Diffraction, the ...
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2answers
73 views

Commercially available material with highest density to cost ratio? [closed]

What are the top 5 commercially available materials (not limited to just the elements) with the highest density to cost ratio? To point to an application, say that my goal was to mass produce a solid ...
3
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0answers
79 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 ...
0
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1answer
252 views

2 Extra Degree of Freedom in Linear Triatomic Molecules?

Ok, there is a bit problem in understanding Degree of Freedom of Linear Molecules specially of Triatomic Linear Molecules. See, the DOF in general is given as $f=3N-k$. Here, N=Number of atoms in a ...
3
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1answer
110 views

How does the graph of molar heat capacity point towards quantization of motion?

In the graph below, if we consider that the jumps are stepwise for a molecule, even then, how does it point toward quantization of vibrational and rotational motion? The thing it implies is that (...
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0answers
67 views

How to write a wave function for two entangled photons in a (J,P)=($0$,+) state?

I'm studying some experiments using pairs of atomic photons, in particular those photons that are consequence of the $(J=0)\rightarrow(J=1)\rightarrow(J=0)$ cascade of calcium. All of them start ...
2
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2answers
61 views

For a molecule, does the term 'thermal vibration' mean the same thing as 'molecular vibration'?

When speaking of a molecule, do both terms ('thermal vibration' and 'molecular vibration') describe the same thing, being the one and only periodic motion of the atoms within the molecule? Or, are ...
7
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2answers
744 views

Classical theory fails to explain quantization of motions?

I understand everything written here. But the last point, I cannot get, at all. How does it point towards Quantization of the two motions, since the energy change is not sudden, but gradual? And if ...
0
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2answers
238 views

What is the difference between intermolecular (cohesive, adhesive) and van der Waals force?

I recently learnt that intermolecular force is the force of attraction between molecules and van der Waals force does the same so is there any difference ?
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0answers
16 views

Proof of no. of degrees of freedom for $N$-atom molecule [duplicate]

How can we say that the no. of degrees of freedom for a $N$-atom molecule is $3N$? How to $\mathbb{prove}$ it? I have heard people saying that for each atom, there are 3-independent variables to ...
4
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1answer
76 views

Simple question about molecules leaving a liquid at a temperature below the boiling point

My textbook asks the question why a liquid cools down when partial evaporation occurs just below the surface at a temperature below the boiling point. The answer is of course that only those ...
0
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1answer
78 views

Equipartition of energy and degrees of freedom in Diatomic gas [duplicate]

Suppose we have a gas of $N$ diatomic molecules (ex $O_2$) with one-molecule hamiltonian being: $$\mathcal{H} = \frac{\vec{p}_1^2}{2m}+\frac{\vec{p}_2^2}{2m} + V(r_{rel}) $$ Where $r_{rel}$ is the ...
2
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1answer
102 views

How many elementary particles are contained in a molecule of $H_2O$?

I was wondering about how many elementary particles form up one molecule of $H_2O$. What I thought of is the following: Hydrogen : 0 neutrons, 1 electron, 1 proton; electron is elementary and proton ...
2
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2answers
338 views

Actual Degree of Freedom of Diatomic Molecule

Ok, I have 2 very different values for degree of freedom(DOF) of diatomic molecules arising due to the difference in the vibrational DOF of the diatomic molecules. According to this DOF wiki page:- ...
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2answers
43 views

O2 molecues speed in air, and their limit

Temperature is the proportional measure of kinetic energy of the random motion of the constituent micro particles in a system as per wikipedia. Now I understand that O2 molecules are randomly moving ...
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2answers
52 views

If I would let something mix in the blender and let time go to infinity, will all molecules be separated eventually?

Just question out of curiosity. If I would let something mix in the blender and let time go to infinity, will all molecules be separated eventually, i.e. if I open up the blender it will be gas? Or ...
1
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1answer
93 views

Symmetry of ground state electron configuration

Take a molecule, whose atoms have a symmetry $S\in \text{O}(3)$ (i.e. S permutes the atoms). $S$ also acts on the wavefuncion $\psi(x_1,...,x_n)$ of the $n$ electrons in the molecule, by its action ...
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2answers
48 views

Can we (in principle) obtain molecular bound systems by modelling fundamental particles and their interactions?

Is it possible, at least in principle, to start with the Schrodinger/Dirac/Klein-Gordon equations to model elementary particles and their interactions and to obtain in the end molecular bound systems? ...
2
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0answers
31 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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0answers
34 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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0answers
12 views

Simulating only small parts of macromolecules

I've recently gotten into molecular dynamics (MD), and I was wondering the following: how can one simulate only small parts of proteins, e.g. up to 10AA? I am fond of e.g., Gromacs, where whole ...
0
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1answer
52 views

Surface tension molecular theory

How does the surface of water behave like a stretched membrane? What's the cause for that? I know that the surface molecules experience a net force downward so there is dense layer of water molecules ...
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0answers
26 views

Does a Conical Intersection imply that the HOMO-LUMO gap in a molecule is very small?

I came across some notes in which the author swiftly made this comment, that if there's always a large gap between the HOMO and the LUMO along a chemical reaction ("large" can mean at least bigger ...