Carbon–sulfur chains: A high‐resolution infrared and quantum‐chemical study of C3S and SC7S

In the course of a 5 μm high‐resolution infrared study of laser ablation products from carbon–sulfur targets, the ν₁ vibrational mode region of linear C₃S has been studied continuously from 2046 to 2065 cm^?1. Besides the prominent vibrational fundamental, the region was found to feature the , and even hot bands, the latter two of which were observed for the first time. Owing to the high signal‐to‐noise ratio obtained, the ν₁ mode of S could also be observed in natural abundance for the first time at high spectral resolution in the infrared. At 2061 cm^?1, hidden inside the branch of the C₃S ν₁ fundamental mode, a weak new band is observed which exhibits very tight line spacing and stems from a heavy both carbon and sulfur containing carrier. On the basis of high‐level quantum‐chemical calculations of selected carbon–sulfur chains and other carbon‐rich cumulenes, this feature is attributed to the ν₅ vibrational fundamental of linear SC₇S, which stands for the first gas‐phase spectroscopic detection of this long cumulenic chain.     

Energies for cyclic and acyclic aggregations of adamantane and diamantane units sharing vertices,edges, or six‐membered rings

Diamondoids are hydrocarbons having a carbon scaffold comprised from polymer‐like composites of adamantane cages. This article describes computed total energies and “SWB‐tension” energies (often referred to as “strain” energies) for species having n adamantane or diamantane units sharing pairwise: one carbon atom (spiro‐[n]adamantane or spiro‐[n]diamantane); one C? C bond (one‐bond‐sharing‐[n]adamantane or one‐bond‐sharing‐[n]diamantane); or one chair‐shaped hexagon of carbon atoms (1234‐helical‐cata‐[n]diamantanes). Each of the five investigated polymer‐like types is considered either as an acyclic or a cyclic chain of adamantane‐ or diamantane‐unit cages. With increasing n values, SWB‐tension energies for acyclic aggregates are found to increase linearly, while the net SWB‐tension energies of cyclic aggregates often go thru a minimum at a suitable value of . In all five cases, a limiting common energy per unit ( ) is found to be approached by both cyclic and acyclic chains as , as revealed from plots of versus 1/n for acyclic chains and of versus 1/n² for cyclic chains. © 2015 Wiley Periodicals, Inc.     

Structural,magnetic, and vibrational properties of stoichiometric clusters of CrN

We performed density‐functional‐theoretic calculations to investigate the structural, magnetic and vibrational properties of the stoichiometric clusters (CrN)_n ( ). We show that the building block of the ground‐state structures of these clusters is a square CrNCrN unit; the only exception with n > 2 occurs for (CrN)₃, but this cluster has an isomer not very far in energy from the ground state consisting of a pair of CrNCrN squares sharing a CrN bond. In the smaller CrN, (CrN)₂, and (CrN)₃ clusters the magnetic moments of the N atoms are non‐negligible and antiparallel to those of the Cr atoms, but for the larger species (CrN)₄, (CrN)₅, (CrN)₆, and (CrN)₉ the cluster magnetic moments are almost entirely due to the Cr atoms. Lack of imaginary vibrational frequencies in the predicted ground‐state structures of (CrN)_n ( ) confirms that they are mechanically stable equilibrium states. © 2015 Wiley Periodicals, Inc.     

Theoretical study on the electronic structures and optical properties of blue‐green and blue phosphorescent iridium(III) complexes with tetraphenylimidodiphosphinate ligand

The electronic structures and photophysical properties of five iridium(III) complexes Ir(tfmppy)₂(tpip) (1), Ir(dfppy)₂(tpip) (2), Ir(afCNppy)₂(tpip) (3), Ir(CNpyN₃)₂(tpip) (4), and Ir(2fphpta)₂(tpip) (5) [where tfmppy = 4‐trifluoromethylphenylpyridine; dfppy =4,6‐difluorophenylpyridine; afCNppy = 6‐fluoro‐4‐octyloxy‐5‐cyano‐phenylpyridine; CNpyN₃ = 2‐(4‐cyano‐phenyl)‐[1,2,3]‐triazole; 2fphpta=2‐(2,6‐difluoro‐phenyl‐[1,2,4]‐triazol‐3‐yl)‐pyridine; tpip=tetraphenylimido‐diphosphinate] have been investigated by using density functional theory (DFT) methods and time‐dependent DFT ones, aiming at elucidating the influences of different substituents and cyclometalated ligands on the emission properties and quantum yield. The calculated results revealed that the different substituents in 1 ‐ 3 have a great influence on the energy levels, in particular highest occupied molecular orbital. Meanwhile, we have also get a further insight into the reason for different phosphorescence quantum yields of the studied complexes. The higher quantum yield (Φ) reported for 1 was found to be closely related to both its smaller S₁–T₁ splitting energy ( ) and larger transition electric dipole moment ( ) upon the S₀ → S₁ transition. Complex 5 is expected to be a potential candidate for blue‐emitting material with good organic light‐emitting diodes performances. We propose that the optical properties of this class of materials can be tuned by the modifications of the cyclometalated ligands. © 2013 Wiley Periodicals, Inc.     

Effect of microhydration on the atmospherically important metastable carbonyl sulfide anion: Structure,energetic, and infrared study

Structure, energetics, and vibrational frequency of the microhydrated carbonyl sulfide anion [OCS^?? (H₂O)_n (n = 1–6)] have been explored by the systematic ab initio study to have a comprehensive understanding about the hydration‐induced stabilization phenomenon of OCS^?. Water binds with the OCS^? in single hydrogen‐bonded (SHB) or double hydrogen‐bonded (DHB) fashion with O? H S and O? H O contacts. Maximum five water molecules can stay in a cyclic water network of these hydrated clusters forming interwater hydrogen bonding (IHB) with each other and out of this, maximum of two water molecules can bind directly to the OCS^? in (DHB) arrangement. The stabilization energy values of OCS^?? (H₂O)_n depict that ion–water interaction is significant up to four water molecules and beyond that OCS^? is stabilized by IHB between the water molecules. The CO stretching frequency of OCS^? gets red shifted, whereas CS stretching frequency gets blue shifted on hydration. Charge analysis of hydrated clusters of OCS^? indicates that negative charge moves toward oxygen from sulfur on hydration. © 2015 Wiley Periodicals, Inc.     

Electrocatalytic Synthesis of Ammonia at Room Temperature and Atmospheric Pressure from Water and Nitrogen on a Carbon‐Nanotube‐Based Electrocatalyst

Ammonia is synthesized directly from water and N₂ at room temperature and atmospheric pressure in a flow electrochemical cell operating in gas phase (half‐cell for the NH₃ synthesis). Iron supported on carbon nanotubes (CNTs) was used as the electrocatalyst in this half‐cell. A rate of ammonia formation of 2.2×10⁻³ g m⁻² h⁻¹ was obtained at room temperature and atmospheric pressure in a flow of N₂, with stable behavior for at least 60 h of reaction, under an applied potential of −2.0 V. This value is higher than the rate of ammonia formation obtained using noble metals (Ru/C) under comparable reaction conditions. Furthermore, hydrogen gas with a total Faraday efficiency as high as 95.1 % was obtained. Data also indicate that the active sites in NH₃ electrocatalytic synthesis may be associated to specific carbon sites formed at the interface between iron particles and CNT and able to activate N₂, making it more reactive towards hydrogenation.     

Comments on the carbon cluster C60 and on its complexes with alkaline elements

We have analyzed in the Hartree–Fock approximation the carbon cluster C₆₀ with a single-zeta [(9,5)/(2,1)] basis set and a double-zeta [(9,5)/(4,2)] basis set, the latter with and without 3d polarization functions. Estimates of the correlation energy correction were obained either using Becke's density functional theory or the Clementi–Chakravorty's electron–pair density approximation. The cluster's positive ion and singly and doubly charged negative ions have also been studied (doublets for C and C and singlet and triplet for C) and computed both with a doublezeta basis set and defferent geometries or a double-zeta plus polarization basis set. The geometries considered include the one obtained by quantum molecular dynamics using the Car–Parrinello approximation and two additional near this minimum. The computed ionization potential and electron affinity are in reasonable agreement with the experiments considering the basis sets adopted. A lithium, a sodium, or a potassium atom or the corresponding positive ions have been placed at the center of the cluster and have been shown to form stable complexes: C₆₀Li⁺, C₆₀Li, C₆₀Na⁺, C₆₀Na, C₆₀K⁺, and C₆₀K. In addition, preliminary data with a calcium atom are reported. Computations on model cluster C₅, C₆, and C₉ are also reported to show that one needs large basis sets, extended use of polarization functions, and correlation corrections for quantitative results, more accurate than ～5 kcal/mol per carbon atom, in the total energy, as in this work.     

Quantum control of electron‐proton symmetry breaking in dissociative ionization of H2 by intense laser pulses

Forward and backward electron/proton ionization/dissociation spectra from one‐dimensional non‐Born‐Oppenheimer H₂ molecule exposed to ultrashort intense laser pulses ( W/cm², λ = 800 nm) have been computed by numerically solving the time‐dependent Schrödinger equation. The resulting above‐threshold ionization and above‐threshold dissociation spectra exhibit the characteristic forward‐backward asymmetry and sensitivity to the carrier‐envelope phase (CEP), particularly for high energies. A general framework for understanding CEP effects in the asymmetry of dissociative ionization of H₂ has been established. It is found that the symmetry breaking of electron‐proton distribution with π periodic modulation occurs for all CEPs except for ( integer) and the largest asymmetry coming from the CEP of . At least one of the electron and proton distributions is asymmetric when measured simultaneously. Inspection of the nuclear and electron wave packet dynamics provides further information about the relative contribution of the gerade and ungerade states of to the dissociation channel and the time delay of electrons in asymmetric ionization. © 2014 Wiley Periodicals, Inc.     

Design of neutral organic superacids using fulvene derivatives with di‐enol substituent

A new class of superacids was designed using enolic derivatives of fulvene. After deprotonation, bond rearrangement leads in a stable conjugate base with an aromatic cyclopentadienyl ring and a carboxyl group. The gas phase enthalpies ( ) of the deprotonation, as an index of acidity, were calculated employing the B3LYP method and 6‐311++G(d,p) and aug‐cc‐PVDZ basis sets. The acidity of these compounds without any electron withdrawing groups was more than H₂SO₄ in gas phase. The acidity increased by substituting electron withdrawing groups (? F, ? CN, and ?O) into the molecules so that we could achieve a cyano derivative of fulvene with = 250 kcal/mol.     

Determination of heisenberg exchange coupling constants in clusters with magnetic sites: A local spin approach

This work studies the ability of the two‐center local spin quantities, provided by the partitioning of the expectation value of the spin‐squared operator corresponding to N‐electron systems, for determining spin‐exchange coupling constants within the Heisenberg spin Hamiltonian model. The spin‐exchange parameters, which characterize this Hamiltonian for a determined system, have been evaluated in the HeH₂ aggregate and in several clusters (n = 2, 3, 4) with different geometrical arrangements, using internuclear distances larger than the equilibrium ones (beyond the bonding regions). The results found have been analyzed and compared with those arising from other approaches, showing the feasibility of our methodology. © 2014 Wiley Periodicals, Inc.     

Prediction of the pH‐rate profile for dimethyl sulfide oxidation by hydrogen peroxide: The role of elusive H3O2+ Ion

Experimental kinetics of sulfide oxidation by hydrogen peroxide presents a pH‐dependent profile. In this article, it was carried out a detailed study of the mechanism and kinetics of dimethyl sulfide (DMS) oxidation by H₂O₂ in neutral, acid, and basic aqueous medium using ab initio calculations. The results point out that DMS oxidation in neutral aqueous medium occurs through its direct reaction with H₂O₂. In acid medium, cluster‐continuum model calculations shows that cluster is the best representation of the very reactive species. In basic medium, there is formation of the species. However, the pathway involving this species has high free energy barrier, making this pathway unfeasible. The theoretical pH‐rate profile is in good agreement with the experimental observations. © 2013 Wiley Periodicals, Inc.     

Synthesizing quantum probability by a single chaotic complex‐valued trajectory

The current trajectory interpretation of quantum mechanics is based on an ensemble viewpoint that the evolution of an ensemble of Bohmian trajectories guided by the same wavefunction Ψ converges asymptotically to the quantum probability . Instead of the Bohm's ensemble‐trajectory interpretation, the present paper gives a single‐trajectory interpretation of quantum mechanics by showing that the distribution of a single chaotic complex‐valued trajectory is enough to synthesize the quantum probability. A chaotic complex‐valued trajectory manifests both space‐filling (ergodic) and ensemble features. The space‐filling feature endows a chaotic trajectory with an invariant statistical distribution, while the ensemble feature enables a complex‐valued trajectory to envelop the motion of an ensemble of real trajectories. The comparison between complex‐valued and real‐valued Bohmian trajectories shows that without the participation of its imaginary part, a single real‐valued trajectory loses the ensemble information contained in the wavefunction Ψ, and this explains the reason why we have to employ an ensemble of real‐valued Bohmian trajectories to recover the quantum probability . © 2015 Wiley Periodicals, Inc.     

A theoretical study on cyclacenes: Analytical tight‐binding approach

We present a theoretical study of cyclacene molecules performed at tight‐binding level. The orbital energies and eigenvectors have been analytically computed, and exact expressions for the axial component of the total position spread and polarizability tensors have been obtained. In absence of dimerization, the system has a D_nh symmetry, where n is the number of hexagonal units. The energy bands present no gap at the Fermi level, and to this fact it corresponds a diverging (per‐electron) polarizability for in the direction of the system symmetry axis. The two (degenerate) components of the polarizability on the σ_h symmetry plane, conversely, remain finite for . The total position spread tensor presents a qualitatively different behavior, since all the three components of the position spread per electron remain finite for . The results are analyzed and discussed for both axial and planar components separately as these are affected differently with respect to the increasing system size. Both dipole polarizability and total position spread have been computed using an ab initio approach for the smallest systems, to compare the analytical tight‐binding expressions with a higher‐level theory.     

Theoretical investigation of geometry and stability of small lithium‐iodide LinI (n = 2–6) clusters

We present theoretical investigation of the structural characteristics and stabilities of neutral and positively charged Li_nI (n = 2‐6) species. The structural isomers were found by using a randomized algorithm to search for minima structures, followed by B3LYP optimizations; the single‐point RCCSD(T)/cc‐pwCVTZ(‐PP) calculations were performed in order to compute relative energies, binding energies per atom, adiabatic and vertical ionization energies, and dissociation energies. Stability was compared to the pure lithium clusters; there is a typical odd‐even alternation; iodine doped clusters are more stable than pure lithium clusters. Lithium “cage” transfers its valence electron to the iodine atom to form neutral and cationic clusters. An electron departures the lithium cage upon ionization. An important reason for the larger stability of closed‐shell species is the existence of the HOMO 3c/2e natural bond orbitals. © 2013 Wiley Periodicals, Inc.     

Theoretical prediction of the optical rotation of chiral molecules in ordered media: A computational study of (Ra)‐1,3‐dimethylallene, (2R)‐2‐methyloxirane,and (2R)‐N‐methyloxaziridine

A theoretical procedure has been developed and implemented to calculate the optical rotation of chiral molecules in ordered phase via origin‐independent diagonal components , of the optical activity tensor and origin‐independent components , for , of the mixed electric dipole‐electric quadrupole polarizability. Origin independence was achieved by referring these tensors to the principal axis system of the electric dipole dynamic polarizability at the same laser frequency ω. The approach has been applied, allowing for alternative quantum mechanical methods based on different gauges, to estimate near Hartree–Fock values for three chiral molecules, (2R)‐N‐methyloxaziridine C₂NOH₅, (2R)‐2‐methyloxirane (also referred to as propylene oxide) C₃OH₆, and ( )‐1,3‐dimethylallene C₅H₈, at two frequencies. The theoretical predictions can be useful for an attempt at measuring correspondent experimental values in crystal phase. © 2015 Wiley Periodicals, Inc.     

Unexpected properties of non‐autoionizing doubly excited states of the H2 molecule

We present accurate calculations of the non‐autoionizing and doubly excited states of the H₂ molecule using full configuration interaction with Hartree–Fock molecular orbitals and Heitler–London atomic orbitals. We consider the united atom configurations from He(2p2p) up to He(2p8g) and dissociation products from H₂(2p + 2p) up to H₂(2p + 6?). Born–Oppenheimer calculations are carried out with extended and optimized Slater‐type orbitals for a total of 40 states, 10 for each symmetry, covering the internuclear distances from the united atom to dissociation, which, for some states, is reached beyond 100 a₀. Occurrences of repulsive states cleanly interlaced between bound states with many vibrational levels are reported. Some of the potential minima are deep enough to accommodate many vibrational levels (up to 50). Noteworthy large equilibrium minima, like R_eq = 46.0 a₀ in the state dissociating as (2p + 6h) and with 18 vibrational levels. The occurrence of vertical excitations from the singly excited manifolds is analyzed. Several states present double minima generated by avoided crossings, some with a strong ionic character. © 2016 Wiley Periodicals, Inc.     

Lanthanide metals in the boron cages: Computational prediction of M@Bn (M = Eu,Gd; n = 38, 40)

Endohedral metalloborofullerenes (EMBFs) are novel boron analogues of the famous endohedral metallofullerenes (EMFs). Many EMBFs have been proposed by theoretical calculations thus far. However, in sharp contrast to EMFs, which trap most of the lanthanides with f electrons inside the cages, the corresponding lanthanide‐based EMBFs have never been reported. In this work, the encapsulation of Eu and Gd in the B₃₈ and B₄₀ fullerenes was studied by means of density functional theory calculations. Our results revealed that Gd@B₃₈(⁹A), Eu@B₄₀(⁸B₂), and Gd@B₄₀(⁷A″) all favor the endohedral configuration, and the electronic structures can be described as Gd³⁺@ , Eu²⁺@ , and Gd³⁺@ with jailed f electron spins. The large binding energies and sizable HOMO–LUMO gaps suggest that they may be achieved experimentally. They feature σ and π double aromaticity, and their excellent stabilities were confirmed by the Born–Oppenheimer molecular dynamics simulations. Finally, the infrared and UV/vis spectra were simulated to assist experimental characterization.     

The nature of the chemical bond in borazine (B3N3H6), boroxine (B3O3H3), carborazine (B2N2C2H6), and related species

The bonding problem in borazine (B₃N₃H₆), boroxine (B₃O₃H₃), and carborazine (B₂N₂C₂H₆) is successfully addressed through the consideration of the excited states of the constituent fragments, namely BH( ), NH( ), and CH( ). We propose the participation of resonant structures for all three species that help to explain the experimental findings. A discussion on the chemical pattern of the parental molecule benzene (C₆H₆) helps to make coherent the whole bonding analysis on the titled species.     

Electron‐density delocalization in many‐electron atoms confined by penetrable walls: A Hartree–Fock study

The electronic structure of several many‐electron atoms, confined within a penetrable spherical box, was studied using the Hartree–Fock (HF) method, coupling the Roothaan's approach with a new basis set to solve the corresponding one‐electron equations. The resulting HF wave‐function was employed to evaluate the Shannon entropy, , in configuration space. Confinements imposed by impenetrable walls induce decrements on when the confinement radius, R_c, is reduced and the electron‐density is localized. For confinements commanded by penetrable walls, exhibits an entirely different behavior, because when an atom starts to be confined, delivers values less than those observed for the free system, in the same way that the results presented by impenetrable walls. However, from a confinement radius, shows increments, and precisely in these regions, the spatial restrictions spread to the electron density. Thus, from results presented in this work, the Shannon entropy can be used as a tool to measure the electron density delocalization for many‐electron atoms, as the hydrogen atom confined in similar conditions.