Unanswered Questions
1,263 questions with no upvoted or accepted answers
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How to calculate transition dipole moment from two known wavefunctions
I'm interested in calculating the transition dipole moment (TDM) from the information from two wavefunctions of different states. This is somewhat similar to calculating the molecular dipole moment ...
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0
answers
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What is d-orbital collapse?
When I was perusing the works of Schwarz on atomic structure, I came across the unfamiliar term of d-orbital collapse.
He describes it as a variation in energetic sequence from group 1 to 3 elements ...
- 60k
15
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0
answers
357
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Rotation around CC bond in 1,2-dioxetane: transition states and local minimum structures
TLDR:
What: Potential energy surface associated with rotation around CC bond in the ring-opened version of 1,2-dioxetane.
How: State average(4)-CASSCF(12,10)/VTZP constrained geometry optimizations ...
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12
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answers
309
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Accuracy of quantum chemistry calculations on iodine neglecting relativistic effects
Triiodothyronine is a molecule with three iodine atoms. If we attempted to calculate its properties with ab initio methods like Hartree-Fock or more complicated ab initio methods which included ...
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Understanding two-electron integrals in Gaussian 09
I was comparing the two-electron integrals (electron repulsion integrals, ERI) printed by various well-established packages (Gaussian, GAMESS, Molpro etc.) and observed that Gaussian is the oddball in ...
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11
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1
answer
303
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What is this golden looking substance?
I am currently messing around with gallium compromising aluminum. I am using a titalium lock which is just a brand of aluminum padlock and I put a gallium-indium euctic alloy on the surface of it. It’...
CommunityBot
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10
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0
answers
141
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Using symmetry and group theory arguments to explain iron(II) in a tetrahedral crystal field
I am trying to figure out how to explain $1s \rightarrow 3d$ spectroscopic transitions for $\ce{Fe^{2+}}$ in $T_\mathrm{d}$ symmetry. These transitions make up the pre-edge region in K edge X-ray ...
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10
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Why does the reaction of sodium nitrate, aluminium, and sodium hydroxide yield ammonia?
From Russian test problem 4301:
$$\ce{3NaNO3 + 8Al + 5NaOH + 18H2O -> 8Na[Al(OH)4] + 3NH3(g)}$$
How does ammonia evolve here? Is it that we get hydrogen gas evolving in the reaction between Al and ...
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10
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640
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Identifying alkyl ligands as π-donors or π-acceptors in transition metal complexes
Is there a systematic way to identify an alkyl ligand as a π-acceptor or π-donor in a transition metal complex?
Although various sources indicate that the weak field ligands are typically π-donors and ...
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9
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Why are vapours of xenon hexafluoride coloured?
According to Wikipedia,
[...] It is a colorless solid that readily sublimes into intensely yellow vapors.
It is clear from the above statement that $\ce{XeF6}$ is colourless in solid form. But why ...
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9
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0
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Is there a reliable chemical theory that predicts pKa based on structure?
Obviously, there are general stability arguments that can be made to estimate relative pKas, such as evaluating the stability of the conjugate base of an acid, or thinking about how polarized the bond ...
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9
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430
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Vanishing integral rule for two-electron integrals
I understand the vanishing integral rule for a one-electron integral to be:
$$\langle i | \hat{O} | j \rangle = 0 \hspace{1cm} \mathrm{if} \hspace{0.2cm} \Gamma_O \neq \Gamma_i \otimes \Gamma_j$$
...
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9
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0
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514
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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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9
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Order of Basicity of Nitrogen Trihalides
I was asked to arrange nitrogen tri-halides in order of increasing basicity. On looking up the answer online, it turned out to be the following: $\ce{NF3}$ < $\ce{NCl3}$ < $\ce{NBr3}$ < $\ce{...
CommunityBot
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8
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Why is octaoxygen diamagnetic?
I tried considering that according to LCAO-MO theory $\ce{O2}$ is paramagnetic, which is confirmed by experimental evidence. Since octaoxygen has the crystal structure in figure, I thought there is a ...
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207
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Where is bifurcation situated on cyclohexane isomerisation PES?
I am wondering what does PES for cyclohexane isomerisation looks like.
I have two possibilities in mind but each has some kind of vagueness.
1) Starting from boat conformation minimum, followed by ...
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347
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Isolating radium oxide
Why is radium oxide yet to be isolated when a wide range of other radium (II) compounds are known ?
- 6,801
7
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0
answers
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Type of British porcelain invented around 1917-1918
Being subscribed already for 30 years on Scientific American, I recently downloaded the whole archive, and I am now going through 1914-1918.
In the 26 January 1918 issue, on page 95, there is a small ...
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7
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0
answers
101
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Why do nuclei move considerably slower than electrons
I've been trying to learn quantum chemistry at an introductionary level. While reading I've found out that the Born-Oppenheimer approximation seems to be the reason for the basic and crucial model of ...
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7
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593
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Does solvate isomers exist for coordination compounds with ammonia solvent as ligand?
I could find many sources confirming the hydrate isomerism(with water as solvent) but I couldn't find any information about any other solvent. In all the sources "hydrate/solvate isomerism" ...
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7
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Additional example determining Marcus parameters searched
Background / theory: The electron transfer in organic materials was formalized by the Marcus theory, introducing $|H_{ab}|$ to describe the how molecules (or more generally: sites) are coupled with ...
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240
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Why does lithium aluminium hydride appear grey?
Commercial lithium aluminium hydride is a grey compound, which loses a lot of reactivity the darker it is. Luckily you can clean it up to get the reactive white compound and the separated grey ...
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7
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Why isn't orthoboric acid soluble in cold water even though it has polar B-OH bonds?
This is the information I found regarding orthoboric acid's solubility:
Textbook (NCERT India): Sparingly soluble in water (didn't say what temperature - presumably cold) and highly soluble in hot ...
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7
votes
0
answers
109
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How well will molten iron chrysolite (fayalite) react with hydrogen?
The equation balances nicely, but would the reaction tend to proceed this way? What temperature and time would be needed?
$\ce{Fe2SiO4 + 2H2 -> 2H2O + 2Fe + SiO2}$
There is no problem with ...
- 6,801
7
votes
1
answer
448
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Is there a selective wet etch of Bi2O3 Bismuth Oxide?
I'm looking for a wet etch of Bismuth Oxide that does not etch $\ce{Bi}$ itself.
There are obviously chemicals that etch $\ce{Bi2O3}$, but $\ce{Bi}$ is pretty fragile, so almost everything I've found ...
CommunityBot
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7
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Is there a difference between hydrated oxides and hydroxides?
My guess is that they are different.
I think hydrated oxides would have a lattice with the cation and oxide anions as lattice points and molecules of water trapped in interstitial spaces, while ...
7
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0
answers
379
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What is the most accepted explanation of aurophilicity?
Gold has a special property called aurophilicity. Inorganic chemistry by Huheey has some explanation, but that was not enough to clear the conception.
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7
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547
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Ligand strength - Coulombic effect and/or Electronegativities?
According to my teacher, these three Lewis bases generally decrease in strength in the following order:
Ammonia
Water
Hydroxide ion
I agree. However, he argues that their ability to act as Lewis ...
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7
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1
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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 ...
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6
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0
answers
451
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How to explain oxidizing power from Molecular Orbital Theory
I am trying to explain the oxidizing property of $\ce{Fe^3+}$ in $\ce{H2O}$ and $\ce{CN^-}$ which is $\ce{[Fe(H2O)6]^3+}$ and $\ce{[Fe(CN)6]^3-}$.
The electrochemical reactions along with their ...
CommunityBot
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6
votes
0
answers
78
views
Why SCF-MO methods fail when treating bond-breaking processes?
I'm currently studying the EVB(Empirical Valence Bond) approach. While reading on this article (https://pubs.acs.org/doi/10.1021/ja00224a011), the author mentioned about the usage of SCF-MO formalism ...
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6
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Obtaining transition density matrix
I'm trying to assemble a transition density matrix on quantum computer using one-body excitation $\widehat{E}$ operator on 2 active spatial orbitals, i.e. on 4 spin-orbitals. The problem is, I need to ...
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6
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Are there examples of publications using DFT instead of HF as a coupled-cluster reference?
I have been searching for a while, and only managed to find an article by M. Saitow,[1] where CAM-B3LYP orbitals are used. I was wondering if this has been done elsewhere.
It was recommended to me by ...
- 44.3k
6
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192
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Hund's rule for comparing term symbol energies in excited state
This question was asked in an exam:
The lowest energy electronic state for excited state carbon atom is,
a. $^1D_2$
b. $^3D_1$
c. $^3D_3$
d. $^3D_2$
Although we have been taught Hund's rule for ...
- 7,030
6
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0
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114
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Solving the Schrödinger equation for a rotating triatomic linear molecule
This source is showing that solving the Schrödinger equation for a triatmoic linear molecule yields the same formula for the rotationaI quantum states $BJ(J+1)$ as for dipoles.
For dipoles, the total ...
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6
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90
views
How long would it take for a tank of same-spin hydrogen atoms to become a tank of H₂?
In the question
Is there an energy cost associated with flipping the spin of an electron?, it is shown that it is very unlikely for two hydrogen atoms to bond if their electrons have the same spin. ...
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6
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573
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How to extract force constants for normal modes from ORCA?
I am following the computational method described in Scientific Reports.[1] Where the authors analyze the contribution of each excited state normal-modes to the shift of the transition energy. For ...
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Why are B-O-H and B-O-C angles in B(OH)3 and B(OCH3)3, respectively are higher than normal?
In Concise Inorganic Chemistry by JD Lee (4th edition; adapted by Sudarshan Guha), page 77 under the topic "Back Bonding" it is given:
The $\mathrm{2p}\pi$-$\mathrm{2p}\pi$ back bonding in $\ce{B(...
- 2,090
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383
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How to evaluate the expectation value of the Hamiltonian for a three electron Slater determinant?
I'm having trouble with a few concepts dealing with slater determinants and many electron systems. In particular, when dealing with 3 electron systems, I know that
$$
\psi_0 = \frac{1}{\sqrt{6}} \det
...
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Does fluoride anion ever act as a strong field ligand?
In the case of $\ce{[Fe(H2O)6]^3+}$ there are $5$ unpaired electrons as water acts as a weak field ligand. But instead of fluoride acting as a weak field ligand in the $\ce{[MnF6]^4-}$ , why does it ...
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6
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201
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Vibrational Self-Consistent Field
There are a few things about VSCF that I don't understand:
Which coordinates do you work in? If you work in normal mode coordinates, how do you evaluate the effect of the average of one normal mode ...
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6
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Why is the N-N bond length greater in dinitrogen trioxide than in dinitrogen tetroxide?
Why is the N-N bond length greater in dinitrogen trioxide than in dinitrogen tetroxide?
If the lone pair on $\ce{N}$ in $\ce{N2O3}$ delocalises, then the $\ce{N-N}$ bond will have a double bond ...
- 1,644
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Platt's Notation/Nomenclature for transitions
How do you read Platt's Notation / Nomenclature? Where can I learn this?
Some examples where I've seen this mentioned:
In Platt's notation the transitions are designated as $\ce{A -> B}$ and $\ce{...
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885
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Coordination Numbers and Hybridization schemes of anions
Draw the molecular structures of
(a) the borax anion, $\ce{[B4O5(OH)4]^2-}$
(b) the peroxoborate anion, $\ce{[B2(O2)2(OH)4]^2-}$
...
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Program to compute multipoles of water at CCSD(T)-F12 accuracy
I want to compute traceless cartesian electrostatic multipole moment tensors up to fourth order (hexadecapole), at CCSD(T)-F12 accuracy using a large basis set. I'd like to be able to choose the ...
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333
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How to define the initial guess for the electron density?
This is a technical question. If I have a one-dimensional box of length L, and an electron density existing in the box and integrating to N electrons. And if I want to determine the electron density ...
6
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I found transition states (TS), but calculations aren't supported by experiment. Do I look for more TSs or somewhere else?
I'm using Gaussian to investigate a catalyst system.
Experimental evidence showed that one of three analogues (R = phenyl, Ph), yielded a benzosultam
when treated with 2,4,6-...
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6
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Mechanism for the decomposition of HI
I've been trying to find the mechanism for the gas phase decomposition of hydrogen iodide:
$$\ce{ 2 HI (g) <=> H2 (g) + I2 (g)} $$
Anyone know of sources where I can get information on this? I ...
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2k
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How to compare the oxidizing power of perhalate ions
In my book the oxidizing power in descending order of the following is given as: $\ce{BrO4-} > \ce{IO4-} > \ce{ClO4-}$
My doubt is regarding their order of oxidizing tendency.
I thought that ...
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6
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Methylation of perchlorate
I am exploring (non-experimentally!) the methylation of a perchlorate precursor, either the acid or pre-existing salts, to produce the alkali methyl perchlorate. The methylating agent would be methane ...
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