3 research outputs found
Theoretical Study of Silicon Monoxide Reactions with Ammonia and Methane
High-accuracy calculations were performed
to study the mechanisms
of the reactions between the diatomic silicon monoxide (SiO) with
NH<sub>3</sub> and CH<sub>4</sub>. These reactions are relevant to
the SiO-related astrochemistry and atmospheric chemistry as well as
the activation of the N–H and C–H bonds by the SiO triple
bond. Energetic data used in the construction of potential energy
surfaces describing the SiO + NH<sub>3</sub>/CH<sub>4</sub> reactions
were obtained at the coupled-cluster theory with extrapolation to
the complete basis set limit (CCSDÂ(T)/CBS) using DFT/B3LYP/aug-cc-pVTZ
optimized geometries. Standard heats of formation of a series of small
Si-molecules were predicted. Insertion of SiO into the N–H
bond is exothermic with a small energy barrier of ∼8 kcal/mol
with respect to the SiO + NH<sub>3</sub> reactants, whereas the C–H
bond activation by SiO involves a higher energy barrier of 45 kcal/mol.
Eight product channels are opened in the SiO + NH<sub>3</sub> reaction
including dehydrations giving HNSi/HSiN and dehydrogenations. These
reactions are endothermic by 16–119 kcal/mol (calculated at
298.15 K) with the CCSDÂ(T)/CBS energy barriers of 21–128 kcal/mol.
The most stable set of products, HNSi + H<sub>2</sub>O, was also the
product of the reaction pathway having lowest energy barrier of 21
kcal/mol. Ten product channels of the SiO + CH<sub>4</sub> reaction
including decarbonylation, dehydration, dehydrogenation, and formation
of Si + CH<sub>3</sub>OH are endothermic by 19–118 kcal/mol
with the energy barriers in the range of 71–126 kcal/mol. The
formation of H<sub>2</sub>CSiO + H<sub>2</sub>O has the lowest energy
barrier of 71 kcal/mol, whereas the most stable set of products, SiH<sub>4</sub> + CO, is formed via a higher energy barrier of 90 kcal/mol.
Accordingly, while SiO can break the N–H bond of ammonia without
the assistance of other molecules, it is not able to break the C–H
bond of methane
π‑Conjugated Molecules Containing Naphtho[2,3‑<i>b</i>]thiophene and Their Derivatives: Theoretical Design for Organic Semiconductors
We performed a theoretical investigation
on a series of π-conjugated
organic molecules containing naphthoÂ[2,3-<i>b</i>]Âthiophene
and their derivatives using density functional theory calculations.
All molecules considered exhibit planar structures and aromaticity.
Energy levels of frontier orbitals and reduction and oxidation potentials
of these compounds predicted by our solvation model reveal good agreement
with available experimental values. The UV absorption spectra point
out a clear trend that maximum peaks corresponding HOMO–LUMO
transitions are red-shifted: (i) from compounds containing O to those
containing Se, (ii) from dimers <b>1a</b>–<b>3a</b> and <b>1b</b>–<b>3b</b> to trimers <b>4a</b>–<b>6a</b> and <b>4b</b>–<b>6b</b>, and (iii) from parent compounds <b>1a</b>–<b>6a</b> to perfluorinated derivatives <b>1b</b>–<b>6b</b>. Parent compounds <b>1a</b>–<b>6a</b> can be
considered as p-type semiconducting materials with low reorganization
energies, high transfer integrals, and hole mobility. Perfluorinated
compounds <b>1b</b>–<b>6b</b> are suggested to
be very good candidates for ambipolar semiconducting materials. Introduction
of fused-ring core molecules considerably improves the charge transport
characteristics of the co-oligomers <b>4a</b>–<b>6a</b> and <b>4b</b>–<b>6b</b> as compared to those
of corresponding molecules <b>1a</b>–<b>3a</b> and <b>1b</b>–<b>3b</b>. Accordingly, the former have lower
reorganization energies, higher electron transfer integrals, and higher
rates of charge hopping
Structures, Thermochemical Properties, and Bonding of Mixed Alkaline-Earth-Metal Silicon Trimers Si<sub>3</sub>M<sup>+/0/–</sup> with M = Be, Mg, Ca
The
ground state geometries, electronic structures, and thermochemical
properties of binary alkaline-earth-metal silicon clusters Si<sub>3</sub>M with M = Be, Mg, Ca in neutral, cationic, and anionic states
were investigated using quantum chemical computations. Lowest-lying
isomers of the clusters were determined on the basis of the composite
G4 energies. Along with total atomization energies, thermochemical
parameters were determined for the first time by means of the G4 and
coupled-cluster theory with complete basis set CCSDÂ(T)/CBS approaches.
The most favored equilibrium formation sequences for Si<sub>3</sub>M clusters emerge as follows: all Si<sub>3</sub>M<sup>+/0/–</sup> clusters are formed by attaching the M atom into the corresponding
cation, neutral and anion silicon trimer Si<sub>3</sub><sup>+/0/–</sup>, except for the Si<sub>3</sub>Mg<sup>+</sup> and Si<sub>3</sub>Ca<sup>+</sup> where the metal cations are bound to the neutral Si<sub>3</sub>. The resulting mixed tetramers exhibit geometrical and electronic
features similar to those of the pure silicon tetramer Si<sub>4</sub><sup>+/0/–</sup>. Electron localization function (ELF) and
ring current analyses point out that the σ-aromatic character
of silicon tetramer remains unchanged upon substituting one Si atom
by one alkaline-earth-metal atom