Low-lying Isomers Research Articles

Small lithium-chloride clusters: Superalkalis, superhalogens, supersalts and nanocrystals.

In the present paper, the results of the theoretical investigation of the small lithium-chloride clusters are reported. The geometrical structures, electronic and thermodynamic stability of superalkalis, superhalogens, and their single and double charged ions are obtained using efficient and accurate quantum chemistry methods. Further, low-lying isomers of the Lin Cln ( ) clusters and their stability parameters are calculated. Two ways of formation of the Lin Cln clusters, polymerization of LiCl fragments and combination of superalkalis and superhalogen clusters, are compared. By examination the lattice energy and the average Li-Cl bond length in rectangular Lin Cln ( ) clusters, it was concluded that already 50 LiCl are enough to mostly resembles the structure and stability of the bulk LiCl.

RETRACTED: An Ab initio study on effects of doping into Pt13 cluster with Ag, Ir and Pd

It is well known that doping is an efficient tool to modify the properties of clusters. Here, the results of the ab initio calculations on the effects of substitutional doping of Ag, Ir, and Pd atoms on the atomic and electronic structure of Pt 13 cluster are reported. The plane wave method and spin-polarized Exchange-correlation function have been used to study the various low-lying isomers of Pt 13 and to identify the lowest energy structures of the doped clusters. Moreover, this work involves studying about different doping sites and different magnetization values, exclusively for each isomer. Doing this way, the stability of the atom cluster has been analyzed and that is based on the low energy of the isomers calculated by the total energy with spin-polarized, lowest values of HOMO-LUMO gap, and higher values of the binding energy of each atom in the Pt 13 cluster structure. The resulting lowest energy structures show that in the case of Pt 12 Ir, the lowest energy isomer changes compared to the Pt 12 Ag and Pt 12 Pd clusters. Further, Bader charge analysis has been performed for calculating the charge transfer between the dopant and the host cluster which shows a charge transfer from −1.37 to +0.74 e. The study also reports about the changes that had happened in the electronic structure and magnetic properties of the Pt 13 cluster due to the dopant. This work helps to understand about the energy changes that occur during magnetic moment variations on the atomic cluster, DoS, and about analyzing this energy changes while spinning the atoms. • Effects of substitutional doping of Ag, Ir and Pd atoms with atomic structure of Pt13 cluster. • Study on several low-lying isomers of Pt13 cluster to identify the lowest energy structures of the doped clusters using Exchange-correlation functional methods. • Changes in energy by varying the magnetic moments on the cluster in order to obtain the lowest energy spin isomer. • Usage of Double Triangle, a distorted CDT, FCC-1, Double pyramid, Icosahedron and Decahedron. Total energy calculation on Vertex, Capping and Center doping sites on each isomer.

Theoretical and experimental study of IR spectra of large phenol-acetylene clusters, Ph(Ac)n for 8 ≤ n ≤ 12

This work reports a combined theoretical and experimental study on large phenol-acetylene clusters, Ph(Ac)n, 8 ​≤ ​n ​≤ ​12, extending our earlier work on the smaller clusters [Singh, G.; Nandi, A.; Gadre, S. R.; Chiba, T.; Fujii, A. J. Chem. Phys.2017, 146, 154303]. Several trial cluster geometries are generated using the molecular electrostatic potential (MESP) for placing additional acetylene moieties, followed by geometry optimization at B97D/aug-cc-pVDZ level theory. The infrared spectra of energetically low-lying (within 0.5 ​mH window) isomers of the clusters are calculated and averaged. The O–H stretching band shows two peaks due to the presence of energetically close isomers differing in the arrangement of acetylenes around the O–H group. The acetylenic C–H stretching band appears around 3260 ​cm−1. The C–H band shows a red shift of about 3 ​cm−1 on going from n ​= ​8 to 12. Moderately size-selected IR spectra of Ph(Ac)n (n ​= ​~10 and ~13) prepared by a supersonic jet expansion are measured for the acetylenic C–H region by infrared-ultraviolet double resonance spectroscopy combined with time-of-flight mass spectrometry. The observed spectral features are in agreement with the trends of the frequency shift and asymmetric line shape of the C–H stretch band predicted by the theoretical calculations.

Double σ-Aromaticity in a Planar Zinc-Doped Gold Cluster: Au9Zn.

The strong relativistic effects result in many interesting chemical and physical properties for gold and gold compounds. One of the most surprising findings has been that small gold clusters prefer planar structures. Dopants can be used to tune the electronic and structural properties of gold nanoclusters. Here we report an experimental and theoretical investigation of a Zn-doped gold cluster, Au9Zn-. Photoelectron spectroscopy reveals that Au9Zn- is a highly stable electronic system with an electron binding energy of 4.27 eV. Quantum chemical studies show that the global minimum of Au9Zn- has a D3h structure with a closed-shell electron configuration (1A1'), which can be viewed as replacing the central Au atom by Zn in the open-shell parent Au10- cluster. The high electronic stability of Au9Zn- is corroborated by its extremely large HOMO-LUMO gap of 3.3 eV. Chemical bonding analyses revealed that the D3h Au9Zn- are bonded by two sets of delocalized σ bonds, giving rise to double σ aromaticity and its remarkable stability. Two planar low-lying isomers are also observed, corresponding to a similar triangular structure with the Zn atom on the edge and another one with one of the corner Au atoms moved to the edge of the triangle.

Six Low-Lying Isomers of C11H8 Are Unidentified in the Laboratory-A Theoretical Study.

Isomers of C11H8 have been theoretically examined using density functional theory and coupled-cluster methods. The current investigation reveals that 2aH-cyclopenta[cd]indene (2), 7-ethynyl-1H-indene (6), 4-ethynyl-1H-indene (7), 6-ethynyl-1H-indene (8), 5-ethynyl-1H-indene (9), and 7bH-cyclopenta[cd]indene (10) remain elusive till date in the laboratory. The puckered low-lying isomer 2 lies at 9 kJ mol-1 below the experimentally known molecule, cyclobuta[de]naphthalene (3), at the fc-CCSD(T)/cc-pVTZ//fc-CCSD(T)/cc-pVDZ level of theory. 2 lies at 36 kJ mol-1 above the thermodynamically most stable and experimentally known isomer, 1H-cyclopenta[cd]indene (1), at the same level. It is identified that 1,2-H transfer from 1 yields 2H-cyclopenta[cd]indene (14) and subsequent 1,2-H shift from 14 yields 2. Appropriate transition states have been identified, and intrinsic reaction coordinate calculations have been carried out at the B3LYP/6-311+G(d,p) level of theory. Recently, 1-ethynyl-1H-indene (11) has been detected using synchrotron-based vacuum ultraviolet ionization mass spectrometry. 2-Ethynyl-1H-indene (4) and 3-ethynyl-1H-indene (5) have been synthetically characterized in the past. While the derivatives of 7bH-cyclopenta[cd]indene (10) have been isolated elsewhere, the parent compound remains unidentified till date in the laboratory. Although C11H8 is a key elemental composition of astronomical interest for the formation of polycyclic aromatic hydrocarbons in the interstellar medium, none of its low-lying isomers have been characterized by rotational spectroscopy though they are having a permanent dipole moment (μ ≠ 0). Therefore, energetic and spectroscopic properties have been computed, and the present investigation necessitates new synthetic studies on C11H8, in particular 2, 6-10, and also rotational spectroscopic studies on all low-lying isomers.

Dirac–Fock internal conversion coefficients at low [formula omitted]-ray energy

Presented here are internal conversion coefficients (ICCs) for nuclear transitions of low γ-ray energies from 0.1keV to 1keV in elements with 10≤Z≤118. The low-energy nuclear transitions attract significant interest since the novel experimental technique and methods make it possible to study the transitions as well as to discover new low-lying isomers. Our ICC calculations are shown to be in excellent agreement with experimental data for the fairly low-energy nuclear transitions. The calculations are based on the Dirac–Fock method. The vacancy in the atomic shell from which an electron has been emitted is taken into account in the framework of the frozen core approximation. Experimental binding energies are used for elements Z≤95. Theoretical binding energies obtained in a good approximation are used for Z≥96. Peculiarities of the ICC behavior at low energies are considered. The resonance-like structure of ICC and the drastic decrease in magnitude as the energy increases are demonstrated to be responsible for a pronounced dependence of ICC on theoretical assumptions underlying the calculations. We discuss the influence on the low-energy ICCs of the exact taking account the exchange interaction between electrons, the inclusion of the vacancy after conversion, and a credible choice of the binding energy.

Interstellar Detection of 2-cyanocyclopentadiene, C5H5CN, a Second Five-membered Ring toward TMC-1

Abstract Using radio observations with the Green Bank Telescope, evidence has now been found for a second five-membered ring in the dense cloud Taurus Molecular Cloud-1 (TMC-1). Based on additional observations of an ongoing, large-scale, high-sensitivity spectral line survey (GOTHAM) at centimeter wavelengths toward this source, we have used a combination of spectral stacking, Markov Chain Monte Carlo (MCMC), and matched filtering techniques to detect 2-cyanocyclopentadiene, a low-lying isomer of 1-cyanocyclopentadiene, which was recently discovered there by the same methods. The new observational data also yield a considerably improved detection significance for the more stable isomer and evidence for several individual transitions between 23–32 GHz. Through our MCMC analysis, we derive cospatial, total column densities of 8.3 × 1011 and 1.9 × 1011 cm−2 for 1- and 2-cyanocyclopentadiene, respectively, corresponding to a ratio of ∼4.4 favoring the former. The derived abundance ratios point toward a common formation pathway—most likely being cyanation of cyclopentadiene by analogy to benzonitrile.

Mass measurements of neutron-rich indium isotopes for r -process studies

A new series of neutron-rich indium mass measurements is reported from the TITAN multiple-reflection time-of-flight mass spectrometer (MR-TOF-MS). These mass measurements cover In125−134 (N=76–85) and include ground states as well as isomeric states. The masses of nuclei in this region are known to be of great importance for accurately modeling r-process nucleosynthesis, and the significance of the reported neutron-rich indium masses is discussed in this context. Results are compared with earlier experimental data where available as well as theoretical mass models. The measurements reported here include the first mass measurements of In133,134, as well as the first direct mass measurement of In132. The masses of In125−131 ground states and several isomers were previously measured to higher precision by Penning trap mass spectrometry, which also resolved some low-lying isomers that could not be resolved in this work. The earlier Penning trap measurements serve as excellent cross-checks for the MR-TOF-MS measurements, and in some cases the MR-TOF-MS measurements improve the literature uncertainties of higher-lying isomer masses and excitation energies. A new isomeric state for In128, recently reported for the first time by the JYFLTRAP group, is also confirmed by the TITAN MR-TOF-MS, with a measured excitation energy of 1813(17) keV.Received 24 November 2020Accepted 8 February 2021DOI:https://doi.org/10.1103/PhysRevC.103.025811©2021 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasBinding energy & massesNuclear astrophysicsr processProperties90 ≤ A ≤ 149TechniquesSpectrometers & spectroscopic techniquesNuclear Physics

Beryllium and Magnesium Metal Clusters: New Globally Stable Structures and G0W0 Calculations.

We study the structural and electronic properties of beryllium (Be) and magnesium (Mg) clusters for sizes 2-20 using a two-step approach. In the first step, a global search of the stable and low-lying metastable isomer structures is carried out on the basis of first-principles potential energy surfaces at the level of the generalized gradient approximation (GGA) of density functional theory (DFT). In the second step, vertical ionization potentials (VIPs) and energy gaps between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) are determined using the G0W0 methods for up to the fourth-lowest-energy isomers. Novel globally lowest-energy isomer structures are identified for Be14, Mg14, and Mg16 clusters. The van der Waals interactions are found to have a stronger influence on Mg clusters than on Be clusters. A second-difference analysis for both the binding energies and HOMO-LUMO gaps reveals a close relationship between the structural stability and chemical hardness for both types of clusters.

Th229m isomer from a nuclear model perspective

The physical conditions for the emergence of the extremely low-lying nuclear isomer $^{229m}$Th at approximately 8 eV are investigated in the framework of our recently proposed nuclear structure model. Our theoretical approach explains the $^{229m}$Th-isomer phenomenon as the result of a very fine interplay between collective quadrupole-octupole and single-particle dynamics in the nucleus. We find that the isomeric state can only appear in a rather limited model space of quadrupole-octupole deformations in the single-particle potential, with the octupole deformation being of a crucial importance for its formation. Within this deformation space the model-described quantities exhibit a rather smooth behaviour close to the line of isomer-ground state quasi-degeneracy determined by the crossing of the corresponding single-particle orbitals. Our comprehensive analysis confirms the previous model predictions for reduced transition probabilities and the isomer magnetic moment, while showing a possibility for limited variation in the ground-state magnetic moment theoretical value. These findings prove the reliability of the model and suggest that the same dynamical mechanism could manifest in other actinide nuclei giving a general prescription for the search and exploration of similar isomer phenomena.

Molecular Properties of Bare and Microhydrated Vitamin B5-Calcium Complexes.

Pantothenic acid, also called vitamin B5, is an essential nutrient involved in several metabolic pathways. It shows a characteristic preference for interacting with Ca(II) ions, which are abundant in the extracellular media and act as secondary mediators in the activation of numerous biological functions. The bare deprotonated form of pantothenic acid, [panto-H]−, its complex with Ca(II) ion, [Ca(panto-H)]+, and singly charged micro-hydrated calcium pantothenate [Ca(panto-H)(H2O)]+ adduct have been obtained in the gas phase by electrospray ionization and assayed by mass spectrometry and IR multiple photon dissociation spectroscopy in the fingerprint spectral range. Quantum chemical calculations at the B3LYP(-D3) and MP2 levels of theory were performed to simulate geometries, thermochemical data, and linear absorption spectra of low-lying isomers, allowing us to assign the experimental absorptions to particular structural motifs. Pantothenate was found to exist in the gas phase as a single isomeric form showing deprotonation on the carboxylic moiety. On the contrary, free and monohydrated calcium complexes of deprotonated pantothenic acid both present at least two isomers participating in the gas-phase population, sharing the deprotonation of pantothenate on the carboxylic group and either a fourfold or fivefold coordination with calcium, thus justifying the strong affinity of pantothenate for the metal.

Effects of van der Waals interactions on the structure and stability of Cu8-xPdx (x = 0, 4, 8) cluster isomers

Detailed knowledge of the minimum energy and low-lying structures of metal clusters is crucial to understand their physicochemical properties. In this work, the effect of van der Waals (vdW) interactions on the structure and stability of Cu-Pd clusters is investigated. With this aim, a global search algorithm that combines the basin-hopping method and density functional theory is used to explore the potential energy surface of Cu8-xPdx (x = 0, 4, 8) clusters. We present the structural motifs adopted by the low-energy isomers obtained with the PBE gereralized gradient exchange-correlation functional, and with PBE supplemented by dispersion energy corrections as given by Grimme’s D3 method. The isomeric structures obtained by PBE and PBE-D3 methods are in general quite similar, except for minor changes in some particular isomers. Global structural explorations were also performed with the meta-GGA TPSS and the hybrid PBE0 functionals, showing a reasonable agreement with the results obtained with the PBE and corrected PBE-D3 functionals. The energetics of the clusters is investigated by analyzing the binding energy per atom. Binding ;1;energies become larger when vdW forces are included, and this contribution increases from Cu8 to Pd8 and then to Cu4Pd4. Mixing between Cu and Pd atoms to form nanoalloys is favorable, a feature consistent with the well-known formation of intermetallic compounds in the bulk Cu-Pd alloys. The HOMO-LUMO gap indicates that some isomers in Cu8 and Cu4Pd4 are more reactive than the lowest energy isomer, a feature that gives a hint into the importance that low-lying isomers may have in catalytic reactions. Binding energies and HOMO-LUMO gaps present a stronger dependence on the exchange-correlation functional than the cluster structures.

Transition-metal-like bonding behaviors of a boron atom in a boron-cluster boronyl complex [(η7-B7)-B-BO

Boron displays many unusual structural and bonding properties due to its electron deficiency. Here we show that a boron atom in a boron monoxide cluster (B9O−) exhibits transition-metal-like properties. Temperature-dependent photoelectron spectroscopy provided evidence of the existence of two isomers for B9O−: the main isomer has an adiabatic detachment energy (ADE) of 4.19 eV and a higher energy isomer with an ADE of 3.59 eV. The global minimum of B9O− is found surprisingly to be an umbrella-like structure (C6v, 1A1) and its simulated spectrum agrees well with that of the main isomer observed. A low-lying isomer (Cs, 1A′) consisting of a BO unit bonded to a disk-like B8 cluster agrees well with the 3.59 eV ADE species. The unexpected umbrella-like global minimum of B9O− can be viewed as a central boron atom coordinated by a η7-B7 ligand on one side and a BO ligand on the other side, [(η7-B7)-B-BO]−. The central B atom is found to share its valence electrons with the B7 unit to fulfill double aromaticity, similar to that in half-sandwich [(η7-B7)-Zn-CO]− or [(η7-B7)-Fe(CO)3]− transition-metal complexes. The ability of boron to form a half-sandwich complex with an aromatic ligand, a prototypical property of transition metals, brings out new metallomimetic properties of boron.

Anionic LaH - 8: A Nanocluster-Based Hydrogen Storage Material

The geometric structures of anionic LaH-n (n=2-20) clusters are predicted by CALYPSO cluster structural search method and first-principles calculations. The low-lying isomers for each size of LaH-n (n=2-20) clusters are further reoptimized at B3LYP level by setting all-electron 6-311G++(d, p) basis set for H atoms and SDD basis set for La atom, respectively. The photoelectron spectroscopy (PES) of the ground-state structures are simulated by time-dependent DFT (TD-DFT) method. It is found that the anionic LaH-8 cluster with D2d symmetry is the most stable structure and its hydrogen storage capacity arrives at 5.4 wt%. The stability of anionic LaH-8 cluster is mainly affected by the strong interaction between H 1s orbital and La 5d orbital. The present results provide insights into the further exploration and discovery of novel rare-earth based hydrogen storage nanomaterials.

Structures and Properties of CoB19 +/0/- Clusters.

A global search for the lowest energy structure of Co atom-doped boron clusters (CoB19+, CoB19, and CoB19– clusters) was conducted. The lowest energy structures of them are remarkably different from those of B20 and CoB18– clusters. CoB19+ clusters have a bowl-shaped geometry, where the Co atom is at the bottom of the bowl and is coordinated with eight B atoms. The CoB19 cluster presents seven- and eight-membered B rings. The CoB19– cluster can be viewed as a structure that evolves from a Co-doped boron plane. The coordination number of CoB19 and CoB19– clusters are 16 and 14, respectively. Several low-lying isomers have quasi-planar structures for the CoB19– cluster. Some properties including charge transformation and distribution, HOMO–LUMO gaps, molecular orbital distribution, and stability of neutral CoB19 are discussed. CoB19+ and CoB19– exhibit magnetism with a net moment of 1.0 and 0.94 μB because of odd number of electrons.

Local electrochemical deposition of thorium-229 targets and excitation of isomeric state by electron beam

The results of the study of local formation of thin-film coatings based on thorium oxide on SiO2/Si(111) surfaces by electrochemical deposition. It is shown that as a result of electrochemical deposition of thorium atoms from an acetone solution of Th(NO3)4 with the presence of water on the silicon surface, local formation of thorium compounds occurs. Chemical analysis of the composition of the samples obtained by XPS showed the presence of compounds based on thorium, silicon, oxygen and carbon. It is shown that annealing for 6 hours at 600? C in the atmosphere leads to the departure of carbon, and the formed film consists only of thorium and oxygen. It is shown that such a system can be promising for further studies of the nuclear low-lying isomer transition in the 229Th isotope under electron beam irradiation. The method of excitation of isomeric thorium-229 nuclei by irradiation of a solid-state target based on thorium silicate with an electron beam is considered. The process of generating secondary electrons with a significant increase in the multiplication coefficient for electrons with energies in the range from 1 keV to 25 keV is considered. The values of the output function of isomeric nuclei and the excitation cross section of an isomeric transition in inelastic scattering are obtained on the basis of numerical modeling and theoretical estimation.

Structures and properties of VB5−/0 clusters from density functional theory calculations

Density functional theory with the BPW91 functional and def2-TZVP basis sets was used to investigate the geometric structures of VB5−/0 clusters. By using the bee colony algorithm, 300 initial structures are created for the studied cluster. The geometry optimizations at the BPW91/def2-SVP level result in 18 low-lying isomers in quartet states for the anionic cluster. The results at the BPW91/def2-TZVP level show relative energies and vibrational frequencies for different spin states of 7 isomers of the anionic clusters and 6 isomers of the neutral cluster. It is found that the most stable isomers are A-VB5−/0 with non-planar pentagonal structure. The adiabatic detachment energy of the anionic cluster and the ionization energy of the neutral cluster are 1.93 and 7.36 eV.

High-resolution anion photoelectron spectroscopy of cryogenically cooled 4-atom silicon carbides

High-resolution anion photoelectron spectra of cryogenically cooled , , and obtained using slow photoelectron velocity-map imaging (cryo-SEVI) are presented, providing insight into the geometries, energetics, and vibronic structure of the anionic and the neutral clusters. These spectra yield accurate vibrational frequencies for the neutral clusters. They also yield refined adiabatic detachment energies (ADEs) for the ground states of and of 1.5374(6) eV and 1.9019(4) eV, respectively, while the ADE of a low-lying isomer of is found to be 1.9050(7) eV. The cryo-SEVI spectra show that the ground state of is a distorted trapezoid, and represent the first confirmation of the distorted trapezoid structure of , the only low-lying isomer of this cluster with a permanent dipole moment. Additional transitions are observed from two low-lying anion isomers: a linear structure and a rhombus. The spectrum of , in combination with electronic structure calculations, suggests that the true ground state of is a ring structure with a transannular C–C bond, addressing a longstanding controversy surrounding this cluster. All three spectra exhibit Franck-Condon forbidden transitions; these are attributed to Herzberg-Teller coupling in and and autodetachment from an excited electronic state of .

Microsolvation of Co- in water: Density functional theory calculations coupled with stochastic kicking method.

The hydrated clusters [Formula: see text] (n = 1-4) in gas phase are studied by density functional theory calculations (DFT) coupled with stochastic kicking method. The global minimum structure of [Formula: see text] exhibits low-symmetry pattern since only one H atom of water molecules interact with Co- ion and other ones associate with a network of hydrogen bonds. The Co- ion prefers to locate at vertex site of the water molecular clusters in such way to reduce the repulsion with O atom. These results elucidate the formation of these low-lying isomers are determined by the delicate balance between ion-water and water-water interactions.

Temperature and Nuclear Quantum Effects on the Stretching Modes of the Water Hexamer.

The water hexamer has many low-lying isomers, e.g., ring, book, cage, and prism, shifting from two- to three-dimensional structures. We show that this dimensionality change is accompanied by a drop in the quantum nature of the cluster, as manifested in the red shift of the quantal OH stretching modes as compared with their classical counterparts. We obtain this “nuclear quantum effect” (NQE) as the mean deviation between the OH stretch frequencies from velocity autocorrelation Fourier transforms from classical trajectories on a high-level water potential (MB-pol) as compared with scaled harmonic frequencies from high-level quantum chemistry calculations. With a universal scaling factor, the predicted OH frequencies agree with experiment to a mean absolute deviation ≤10 cm–1, which allows unequivocal isomer assignments. By assuming temperature-independent NQEs, we produce the temperature dependence of the cage isomer OH stretch spectrum below 70 K, where it is the dominant structure. All bands widen and blue-shift with increasing temperature, most conspicuously the reddest mode, which thus constitutes a “vibrational thermometer”.