Questions tagged [physical-chemistry]

The study of chemical systems using the laws and concepts of physics. This usually requires the techniques of thermodynamics, statistical mechanics and quantum mechanics.

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379 views

Single-molecule magnet with electrically-controlled permeability: How does the Titan Shield from Deus Ex work?

In a recent installment of Deus Ex game series there is an augmentation called "Titan Shield" (it has nothing to do with $\ce{Ti}$ element): A neodymium skin underlay matrix built of nano-...
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1answer
4k views

In rovibrational spectra, when exactly is the Q branch forbidden?

I'm aware that the Q branch ($\Delta j = 0$) is usually not observed in rotational-vibrational spectra of diatomic molecules in the gas state, however, I've heard different things about when exactly ...
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142 views

Calculating Triplet-Triplet Spin-Orbit Coupling

According to the Q-Chem manual [1], the singlet-triplet spin-orbit couplings between a singlet excited state $I$ and a triplet excited state state $J$ is: $$\langle\Phi_\text{singlet}^I|\hat{\mathrm H}...
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What is the largest coupled cluster calculation that has ever been done (as of March 2019)?

I am doing some research and trying to make sure the numbers I am reporting are accurate. I found that the paper by Sylvetsky et. al. says:[1] We were, however, able to complete a ...
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In a molecular dynamics context, is the methyl rotation in propene a symmetric or asymmetric internal rotor?

In a prior question, I asked about the (a)symmetry of the potential energy surface of the methyl rotation of propene. In that context, the kinetic energy of the nuclear motions is of course assumed ...
10
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1answer
2k views

Calculation of Atomic weight percentage in AAS

I am currently doing doping studies in a system similar to this ($\ce{A_{x}B_{1-x}}$) and I have to find atomic weight percentage of $\ce{B}$ element using atomic absorption spectroscopy(AAS). I have ...
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443 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 ...
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294 views

What “physical method” does Feynman refer to in The Feynman Lectures on Physics (Vol 1)

In the introductory chapter, Atoms in Motion, of the Feynman Lectures on Physics (Volume One), Feynman alludes to a certain "physical method", which can be used to determine the structure of ...
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193 views

Quenching rates in nucleation MD simulations

I am trying to perform nucleation simulations with molecular dynamics. To prepare the metastable fluid, I am equilibrating at temperatures about 30 K above the melting temperature, and then "quenching"...
8
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1answer
98 views

Will the sulfur-iodine cycle and Haber Method work at lower pressures and temperatures?

I have a year-long research project next year in my senior year of high school, in which we have to make some product or prototype to solve some issue. My interest was in the Liquid Fluoride ...
7
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116 views

Is it possible to calculate electronegativity of surface atoms?

As the title asks, is it possible to calculate the electronegativity (EN) of specific atoms on extended surfaces (slabs), more specifically using computational methods? There are a few issues here I ...
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287 views

Why do chlorinated silanes have lower boiling points than their methane analogs?

The boiling points of the chlorinated silanes and methanes are given below: $$\begin{array}{ccc} \hline \text{Species} & \text{Boiling point (X = Si) / }\mathrm{^\circ C} & \text{Boiling ...
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87 views

What are the limitations of the Born-Lande' equation?

The Born-Lande' equation is used to theoretically calculate the lattice energy, $\Delta U$, of ionic compounds. It is often cited as such in literature, $$\Delta U = -\frac{k_Az_1z_2Me^2}{4 \pi \...
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69 views

Why is concentration used as a proxy for activity instead of mole fraction?

I am trying to understand how the Gibbs energy change of a chemical reaction is computed and I do not understand why concentrations (mol/L) are used as a proxy for activity rather than mole fractions (...
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140 views

Anomaly in van der Waals constants of noble gases

In van der Waals equation for a real gas, the equation is $$\left(P + a\frac{n^2}{V^2}\right)(V - nb) = nRT$$ where $P$ is the pressure of the real gas, $n$ is the number of moles of the gas, $R$ is ...
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317 views

Density of non-ideal vapor mixtures

I'm looking for a reasonably accurate density of a mixture of two gases that act quite unlike ideal gases (generally steam and water-miscible solvents). We can get a first order estimate by taking a ...
6
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405 views

Explaining the photoelecton spectrum of krypton

The photoelectron spectrum of krypton is shown below. (where the x-axis is in electron volts (eV))\ Since both the $3p$ and $3d$ shells are more than half full, based on Hund's rules the lowest-...
6
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1answer
88 views

Beer's law: UV-Vis absorbance values exceeding 2

In classical analytical chemistry, absorbance values in Beer's law can theoretically range from 0 to infinity. As general rule of thumb neither high, nor very low absorbance are used for ...
5
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323 views

Helmholtz double layer

I don't quite understand what is meant by the Helmholtz double layer. Textbooks states something along the lines of: the colloidal particles attain charge by selective adsorption, due to this it ...
5
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104 views

How to calculate a molecule's oscillator strength?

I was wondering how to calculate a molecule's (e.g. biphenyl) oscillator strength using a very simplified model. If I want to calculate a molecule's excited states a good start is something like a ...
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56 views

Computational modeling of steric repulsion between two polymer mediated magnetic Nanoparticle?

Can you recommend any modern article or research papers on steric interactions and forces between two or multiple magnetic nanoparticles with polymer brushes in a nonpolar solvents? something with ...
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312 views

Why does Helium have such a low van der Waals coefficient but not as low a Lennard Jones coefficient?

Helium has the lowest polarizability of any atom, and therefore ought to have the smallest London dispersion force. Indeed, if you look at the van der Waals constant of helium, you find that it has ...
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656 views

What are the factors that affect the redox reactions?

In my work, I used $\ce{Co(OH)2}$ and $\ce{Ni(OH)2}$ as an active materials to fabricate as symmetric supercapacitors in which I used 1-butyl-1-methylpyrrolidinium dicyanamide as an electrolyte. From ...
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657 views

Vapor-pressure or Vapor-concentration

To summarize from my textbook: rate of evaporation: proportional to surface area but essentially independent from pressure (of surrounding gas) rate of condensation proportional to both surface ...
5
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119 views

Raoult's law: is the molar fraction the molar fraction in the entire system?

I have two physical chemistry textbooks, one by Atkins and one by Levine, which seem to differ in their notation used when describing Raoult's law. Atkins talks about the molar fraction term in ...
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5k views

How to calculate the pressure of an ideal gas that undergoes isothermal expansion?

A 2.35 mole sample of an ideal gas, for which $C_{\mathrm{m},v}=3R/2$ initially at $\pu{27 ^\circ C}$ and $\pu{1750 kPa}$, undergoes a two stage transformation. For each of the stages described in the ...
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55 views

Mulliken Spin Density

I would like to know if a Mulliken population analysis to calculate spin densities is in general a valid choice. I see that it is made use of, for example here1. So up to-date researches apparently ...
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22 views

How is the Born-Lande equation modified when the structure is not NaCl?

Often the Born-Lande equation is quoted (alongwith the calculation of the Madelung constant and Born exponent) with reference to rock-salt structure. But what if we take some other crystal, like ...
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58 views

Symmetry Adapted molecular orbitals of Formaldehyde

I am currently trying to find the Symmetry Adapted linear Combinations (SALCs) of Formaldehyde $\ce{H2C=O}$, and use the 1s orbitals on the hydrogen atoms, and 2s, 2px, 2py and 2pz orbitals on the ...
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93 views

Molecular orbital diagram for I₃⁺ cation

Do I need to go through the whole process of reducible representations/projection operator method to come up with the bent SALCs for the $\ce{[I3]+}$ molecule? Or is it simpler than that?
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Has a concept of temperature ever been defined in the context of a single atom?

I wonder if this answer to What would happen if we supercool and then superheat an atom very abruptly? goes far enough. I almost wrote the comment: I don't think we can even talk about the ...
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Is there any publicly available software that can do deterministic CCSDTQP other than MRCC?

MRCC can do arbitrary order coupled cluster but much of the code is computer-generated (not hand-coded by a human) so it can be slow. There are some stochastic codes for high-order coupled cluster, ...
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35 views

Determine the velocity of the O fragment after the dissociation

A $\ce{SO3}$ molecule is radiated with light with a wavelength of $\pu{193 nm}$, which results in photodissociation. $\ce{SO3} + \text{photon}(\lambda=\pu{193nm})\ce{-> SO2 + O}$ It is measured ...
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69 views

Why do old black and white photos fade?

I understand why photos based on organic dyes would fade (discussed previously). But photos based on metallic silver fade as well such as like the one shown below. As a metal (a fairly stable one at ...
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354 views

What is the ANO-RCC basis set and how does it work?

On the basis set exchange, the ANO-RCC basis looks huge, even for hydrogen: ...
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709 views

Atkins' Physical Chemistry 10th edition Question on steady-state approximation

Please help me with Example 20E.2 of Atkins' Physical Chemistry 10th edition textbook on using the steady-state approximation. I have attached my attempt but am just not sure how to get to the final ...
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137 views

Time until completion for $n$-th order reaction

For an $n$-th order reaction, how to determine the time until all the reactants run out? My approach is the following. The reaction kinetics is modeled by the differential equation $$\frac{\mathrm d[...
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184 views

How to verify if a rate law fits the experimental data?

A student after doing an experiment on chemical kinetics, decided that the rate law of the reaction is $u = k[\ce{IO3-}]$ which is correct, but do the data below match with this? Or does he have to ...
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86 views

Can anyone explain this condensation pattern?

What is the hair-like polymer that condenses on the caps of the plastic cell vial? Inside vial are cells in a mixture of FBS and DMSO. The vials were frozen slowly in a special isopropanol-filled ...
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0answers
98 views

Brillouin zones of a compound after structural relaxation

My background in solid-state chemistry isn't much, so I apologize in advance if there arises the need to raise a basic fact while answering my question. I've been learning mostly from the web, with my ...
4
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0answers
2k views

Effect of temperature and pressure on structure of solids

What is the effect of these conditions on the structure of solids? My book has the answer that confuses me. I got nothing about it. Can you please explain? The answer of the book is With the ...
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751 views

Is order of reaction defined for nuclear reactions?

I am asking this question after asking a similar one for spontaneous nuclear decay phy.stack. Link Order of reaction is defined for chemical reaction. But wikipedia says about spontaneous nuclear ...
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352 views

reaction between Green tea and sodium bicarbonate

There is a tea in northern Pakistan called noon chai or Kashmiri chai. It is distinct between it is a pink colour. The method involves brewing green tea leaves in cold water and adding sodium ...
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215 views

Hammett plot shape: dependent on substituent or mechanism?

So, we were shown a Hammett plot that, on the left was linear, but on the right was concave up. How would I explain the shape of the Hammett plot? Does it depend on whether the substituent is an EDG ...
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160 views

Stability of unsaturated syn/anti 3-ladderane

In an oral exam for physical organic chemistry, one student was asked to explain the differences in the ionization potential ($IP$) of syn and anti tricyclo[$4.2.0.0^{2,5}$]octa-3,7-diene (unsaturated ...
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770 views

Why does diamagnetic current induce a downfield while the paramagnetic current induces an upfield shift?

I know that aromatic rings exhibit diamagnetic ring currents which causes the protons outside the ring to go downfield in H-NMR. Antiaromatic compounds exhibit paramagnetic ring currents which have ...
4
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86 views

Computing van der Waals constants from molecular structure

How can van der Waals constants be computed from molecular structure? Is there software that already does this? Is there software that can design a molecule with specified van der Waals constants? ...
4
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0answers
183 views

Howcome orbitals become 'core-like' when electrons are removed?

It seems to me that f-orbitals for lanthanide metals are treated as 'core-like' when a certain number of electrons have been removed. Or, as Radiochemistry puts it, The 4f binding energy is so ...
4
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56 views

Could we bond hydrogen to the edges of covalent network structures like diamond?

I know that diamond is just carbon atoms structured in a way that differs from graphite and charcoal. The carbon atoms on the edges do not have full valence shells. Would it be possible to attach ...
4
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0answers
118 views

Approximate magnetic susceptibility of these liquid propellants?

This question asks if the comparatively large paramagnetic susceptibility of liquid oxygen (LOX) is considered when designing rocket tank and engine systems. This comment suggests fuels such as RP-1 (...

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