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Questions tagged [molecules]

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How to estimate the size of a molecule with examples [on hold]

The distance x is equivalent to the average atomic spacing between two atoms or molecules e.g butter has a density of 1000g/cm3 and a molar mass of 0.018kg/moo. Determine the average spacing of ...
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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
23 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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32 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
46 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
143 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
24 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
38 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
36 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
19 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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3answers
64 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? ...
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2answers
50 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'...
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3answers
60 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 ...
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1answer
86 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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1answer
38 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 ...
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1answer
28 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 ...
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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 ...
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2answers
59 views

Radiation absorption by CO2 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?
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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 ...
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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
70 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 ...
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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 ...
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1answer
159 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 ...
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1answer
107 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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56 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 ...
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2answers
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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 ...
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2answers
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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 ...
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2answers
138 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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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 ...
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1answer
75 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 ...
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1answer
55 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 ...
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1answer
79 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 ...
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2answers
217 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
42 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
51 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 ...
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1answer
60 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
47 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? ...
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0answers
24 views

Determining the sign (+/-) of the total work done on separating two molecules along a certain distance - AMBER16

I am currently moving two sugar molecules apart and would like to analyse the work done on separating them (and thus moving them apart from a distance of 3.5 Å to 30 Å). The values I am given by this ...
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0answers
27 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
32 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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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 ...
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1answer
40 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
23 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 ...
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5answers
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Is Avogadro's law applicable for atoms or just for molecules?

I notice that online definitions of this experimental law always say, molecules or atoms. From the Wikipedia article on Avogadro's Law: $${\frac {V_{1}}{n_{1}}}={\frac {V_{2}}{n_{2}}}$$ The ...
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How can I know the volume occupied by one element in a compound?

I struggle to find how to estimate the volume occupied by one atom in a compound. As an example let's take $\beta$-Ga$_2$O$_3$, since that's the material on which I work the most. The crystal ...
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1answer
103 views

Where will pressure be stronger in these 2 pipe scenarios?

I initially started to be interested in fluid pressure and pipes to learn electricity. It seemed the only way I could help my head to get around some electrical concepts. That's the reason of my ...
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1answer
139 views

Solving linear response in frequency domain

My question stems from a derivation given in chapter 12 of R. McWeeny's Methods of Molecular Quantum Mechanics for solving linear response equations via variational perturbation theory. (Linear ...
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19 views

Literature covering Hund's coupling case and anomalous Zeeman effect

I am taking a course in cold chemistry and different types of interaction seem to be an important cornerstone in the course. I am looking for a book that might cover the topics of molecules in ...
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1answer
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Can you make a metal denser by melting it and make it cool down under high pressure?

The answer is probably no. But can you make a metal denser by melting it and make it cool down under high pressure? Or would it just crack under internal stress when it returns to a solid? I'm going ...