Quantum mechanics is the discipline of physics that focuses on physical phenomenon that occur at an atomic or sub-atomic scale. In particular quantum mechanics attempts to describe the interaction of energy and matter, which can be described using both particle-like and wave-like interactions.

learn more… | top users | synonyms

4
votes
2answers
103 views
+50

Reaction Pathways: What to do when IRC geometries are relaxed (optimized) and the energy changes significantly

The Story: Reaction pathways can be difficult things to deal with using electronic structure methods. Intrinsic reaction coordinates (IRCs) can be determined a number of ways (a discussion of these ...
5
votes
0answers
121 views

Is there an energy cost associated with flipping the spin of an electron?

THE STORY: A common example used to illustrate the limitations of restricted Hartree-Fock (RHF) theory is the H$_2$ dissociation energy ($D_e$) curves. RHF enforces electrons to be paired into spin ...
0
votes
1answer
41 views

What exactly happens to mass during deuterium fusion?

I know that the mass of Helium-4 is slightly less than the mass of 2x Deuterium it may be made of and that it is the reason fusion gives a lot of energy. But where exactly is this missing mass taken ...
3
votes
1answer
32 views

Conservation of angular momentum in electronic transition

My book says the "angular momentum is always conserved in a transition". But if suppose we have a s electron then it's angular momentum is $\hbar\sqrt{l(l+1)}+\hbar\sqrt{s(s+1)}$ $\implies ...
3
votes
1answer
70 views

What does the subscript of atomic orbital mean?

As everyone knows, the atomic orbital can be classified as $s, p_z, p_x, p_y, d_{z^2},d_{xz},d_{yz},d_{xy},d_{x^2-y^2}$ and so on. I want to know the meaning of $z^2,x^2-y^2$ and so on. Maybe this is ...
1
vote
1answer
33 views

Calculate the wavelength of the radiation released when an electron moves from n= 5 to n=2

Calculate the wavelength of the radiation released when an electron moves from n= 5 to n=2. I thought this question was easy. But I did it 5 times and I get the wrong answer every time. I don't know. ...
2
votes
0answers
47 views

Why is the orbital angular momentum of a pi electron along the axis of two atoms' molecule one?

I'm reading quantum chemistry. The book says that the orbital angular momentum of a $\pi$ electron along the symmetry axis of a molecule made up of two atoms is $\pm 1$. I think this is a primary ...
8
votes
4answers
899 views

Why is the alpha particle called a particle when it is made of four particles?

We know the alpha particle is the nucleus of helium. It contains four subatomic particles - two protons and two neutrons. The protons and neutrons are further made of particles called up and down ...
3
votes
2answers
181 views

The energy gap between a pi-conjugated system with (2 bonding and 1 anti-bonding orbital) and (1 bonding and 2 anti-bonding) orbitals

I asked a question previously about "why" it is the case the expanding the size of pi-conjugated systems decreases the required energy to excite an electron from a HOMO to a LUMO band: Why does the ...
4
votes
1answer
134 views

Why are excited Slater determinants used to describe electron correlation?

Usually the first step in describing the electronic wave function of a molecule or atom is to describe it with a single Slater determinant. I get that this is an independent particle approximation, ...
5
votes
3answers
244 views

How to properly relate quantum mechanical energy to the classical world

The Equation of Interest The energy equation derived from the "Particle in a 1-D box" problem is as follows: $E=\dfrac{n^2h^2}{8mL^2}$ where $n$ is the principle quantum number, $h$ is Planck's ...
1
vote
0answers
40 views

Symmetry element in the coversion of cyclopent-2-enyl anion to pentadienyl anion?

I'm trying to draw the state correlation diagram for the reaction of cyclopent-2-enyl anion to pentadienyl anion but I don't know which symmetry element is preserved in this reaction. What could it ...
1
vote
1answer
67 views

Predicting bond-strength of metal carbonyls

The metal carbonyls (and similar organometallic compounds) involve a combination of sigma bond, a pi bond and backbonding. The bond strengths under consideration are the metal-carbon bond and the ...
4
votes
1answer
139 views

Suggest methods and basis sets for a variety of systems

Please help me with any/all of the cases below. In the following cases, the named method and basis set are not suitable for the chemical systems. Why aren't they? Could you suggest a suitable ...
4
votes
3answers
93 views

Why are noble gases stable

I was recently asked the question "Why are noble gases stable? with the expectation of providing an answer beyond the general explanation of "they have full valence layers" and I couldn't think of ...
0
votes
1answer
90 views

Wasn't Rutherford's assumption of gold foil to be made of single layer wrong?

My teacher taught about Rutherford's gold foil experiment today. Sir said that, Rutherford used gold foil of thickness $10^{-7}$ m and concluded atom to be of size $10^{-10}$ m. Sir also said that ...
0
votes
1answer
315 views

Why are wave functions orthogonal?

It seems that all wave functions studied in physical chemistry are orthogonal (e.g. particle in a box, hydrogen atomic orbitals). Does this come about because we purposefully make them orthogonal, or ...
2
votes
0answers
98 views

Magnetic moment of coordination complexes?

To understand the commonly quoted magnetic values of coordination complexes (central ion) we use $$m_l=\sqrt{n(n+2)} \text{BM where BM}=\frac{e\hbar}{2m_e}\text{JT}^{-1}$$ $n$=number of unpaired ...
4
votes
0answers
167 views

Understanding moseley's law from the rydberg-type equation?

To explain the characteristic X-ray emission peaks for various elemental targets, a formula was developed which was similar in construct to the rydberg equation for H-atom as derived by the ...
2
votes
1answer
82 views

How can we write the wave function in quantum mechanics?

In quantum mechanics, while writing the wave functions we can take a product of the spatial and the spin parts.But what does it means? What is the meaning of the spatial wave function and the spin ...
2
votes
3answers
115 views

How do 1s and 2p orbitals overlap?

In the following figure we can see that the p-orbitals overlap 1s orbital (though relatively very little). How can an electron in p-orbital, be simultaneously in the 1s orbital at any given point ...
4
votes
1answer
119 views

Why are the total energies of transition states so commonly corrected for zero-point vibrational energy?

So often I see total energies of transition states corrected for zero-point vibrational energy which always confuses me. Zero point energy is the lowest energy that a ground state molecule can have ...
6
votes
2answers
105 views

How can enzyme/substrate reactions that adhere (largely) to quantum theory also require 'Newtonian' consideration of gravity?

I'd just like to ask for a little clarification here due to confusion from interdisciplinary studies. I'm currently reading the 1976 paper related to the recent 2013 Nobel Prize for Chemistry, by 2 ...
3
votes
1answer
190 views

The Violation Of A Certain Rule or Principle in the following Electronic Configuration

I've to detect the violation of a certain rule or principle in the following electronic configuration: $1s^2,2s^2,2p^1_x,2p^0_y,2p^0_z$ 1) If we test this configuration for $n+l$ rule, then we come ...
5
votes
1answer
79 views

Number of $\pi$-electrons in an energy state

I am learning quantum chemistry and I am trying to understand the statement in a .pdf I'm reading which states "The energy transition associated with the spectral transitions observed is: $$\Delta E = ...
2
votes
1answer
376 views

Calculating the probability of finding an electron between $0.25L$ and $0.75L$ in “particle in a box problem”

If the wavefunction of the electron in a box of length L is $$\psi{(x)}=\sqrt{\frac{2}{L}}\cdot\sin{\frac{n\pi x}{L}}$$ What would be the probability of finding the electron between $0.25L$ and ...
2
votes
1answer
2k views

Nuclear fusion reactions violate law of conservation of mass, but it has not yet been taken into account. Why?

According to the law of conservation of mass, during any physical or chemical changes, the total mass of the products is equal to the total mass of the reactants. But in nuclear fusion reaction if ...
5
votes
2answers
81 views

Is there any difference between a completely filled orbital and an half-filled one?

Is there any reduction in size of the orbital for a half-filled orbital? Is the probability at any point of finding an electron doubled if there are two electrons instead of one? Is there any ...
9
votes
1answer
123 views

Why search new elements?

I've read this today. From the little I know, they discover new elements by bombarding some atoms in particle accelerators (I guess) and these new elements last a few miliseconds. So what's the ...
0
votes
1answer
3k views

How to find the number of valence electrons?

I need to understand the following: Considering an element Sulfur - S which has 16 electrons. How do we calculate the number of valence electrons of S? Please correct me if I am wrong:2+2+6+2+4=16. ...
2
votes
2answers
198 views

Wave function for particle in a infinite well located at -L and +L

The wave function for a particle in a infinite potential well located at $0$ and $L$ is $$\psi_n=\sqrt{\frac2L}\sin\frac{n\pi x}L$$ I want to find our wave function for the same situation where the ...
2
votes
2answers
150 views

Helium empirical wavefunctions

I know that analytic forms of the Helium wavefunctions are not known. However, are there empirical expressions for the low-lying states of Helium? I'd like to use them to calculate some transition ...
2
votes
1answer
295 views

Degeneracy of orbitals?

Why is that in an external magnetic field(uniform) the degeneracy of d,f orbitals is lost but the degeneracy of p orbitals remain intact if the main cause of losing degeneracy is the difference in ...
3
votes
2answers
181 views

Approximation of electron density of a small molecule

Starting point for Quantum Theory of Atoms in Molecules (AIM) is the electron density $\rho(r)$. It could be determined experimentally (X-ray diffractions). I want to know how can we estimate them ab ...
4
votes
2answers
160 views

Did Mendeleev predict the existence of neutrinos?

According to this Wikipedia page, Mendeleev originally believed that the inert gases belonged in Group 0 (to the left of the alkali metals). Thus, helium would be placed in the second period to the ...
3
votes
2answers
3k views

Anomalous Electron Configurations

Cu has an anomalous electron configuration. Cu = $1s^22s^22p^63s^23p^64s^13d^{10}$, it does not follow the usual pattern. In this case, the 3d subshell is filled before the 4s, which usually happens ...
3
votes
1answer
396 views

Quantum dot band gap energy equation

I have been looking into certain approximations for band gap energies in quantum dots and have found this paper (Band-structure-corrected local density approximation study of semiconductor quantum ...
10
votes
1answer
91 views

Is it possible to work out the colour of *any* molecule?

Above are some spectral emission lines for Hydrogen, Helium and Neon. Using the Schrodinger equation, it's possible to derive the colours that Hydrogen will emit when light is fired at it. A ...
5
votes
2answers
331 views

Bonding and anti-bonding orbitals in the light of time-dependent Schrödinger equation?

In organic chemistry, people draw 2p orbitals like this: and then they explain how the orbitals combine to non-bonding (π*) or bonding (π) molecular orbitals, like this: depending on whether the ...
4
votes
2answers
329 views

Why are these molecular orbitals invalid for hexatriene?

Here are the MOs (more accurately, the breakdown of the MOs) for conjugated hexatriene: Now, when first asked to draw the MOs myself, I drew this one for $\psi_3$: It still has two nodes, and is ...
8
votes
2answers
549 views

Why are there quantised energy levels in the vibrational energy of a molecule?

Why are the energy levels for vibrational energy in a molecule discrete as opposed to continuous? I don't understand how a vibration can't have continuous amounts of energy that depend on the ...
5
votes
1answer
122 views

A question about Pauli’s exclusion principle and electron orbital

According to Pauli’s exclusion principle, an $s$ orbital contains at most two electrons with the opposite spin (up and down). Why can't an $s$ orbital contain a third electron whose state is the ...
6
votes
2answers
206 views

Can quantum entanglement affect the chemistry of molecules?

I recently heard a talk from a physicist about experiments on simple two-atom molecules in vacuum that showed that certain behaviour of the molecules was explained by quantum entanglement. Now this ...
3
votes
1answer
84 views

Energy of the n-th level for an atom

Going through the Bohr's model and his assumptions, I came across with this formula to find the energy of the n-th level of any atom: Now, let's say we take as an example the atom of hydrogen, the ...
4
votes
1answer
144 views

Does this set of quantum numbers have a unique solution?

I received the following question: Complete the missing values for the four quantum numbers: $n=?$, $\ell = 2 , m_\ell = 0$ , $m_s= ? $ . The problem is that I think $n$ can be any number ...
1
vote
1answer
344 views

Is there a similar characteristic of the Lanthanide Contraction in the other transition metal groups?

Basically, does this also occur with the 4d, 6d groups as well? I am at a lack of understanding in this topic, I am just wondering what specific elements does this jump in a lower atomic radii occur. ...
3
votes
0answers
78 views

What is the 'ancestral term' in the LS coupling scheme?

On the physics.nist.gov site: http://physics.nist.gov/Pubs/AtSpec/node06.html The table titled "Atomic structural hierarchy in LS coupling and names for the groups of all transitions between ...
1
vote
0answers
124 views

multielectron spin-orbit coupling and energy level

For multi-electron atoms for which the Hamiltonian (including the spin-orbit coupling reads) $$H=\sum_i T_i-Z\sum_i V_i+\sum_i V_i^{\text{s.o.}}+\sum_{i>j}V_{ij}$$ The $T_i$ are the kinetic ...
3
votes
1answer
376 views

Moment of inertia for a triatomic molecule

What does the moment of inertia for a molecule mean? How is it useful? Most importantly, how would I go about solving it for a triatomic molecule?
4
votes
2answers
115 views

Modeling perturbations of a quantum mechanical system

I'm wondering how to properly perturb a quantum mechanical system. I'm looking for a way to express the return to equilibrium of such a perturbed state, where the perturbation is in the Hamiltonian. ...