C2v Symmetry Research Articles

Low-frequency anharmonic couplings in crystalline bromoform: Theory.

Theoretical calculations of the low-frequency anharmonic couplings of the β-phase of crystalline bromoform are presented based on density functional theory quantum chemistry calculations. The electrical and mechanical anharmonicities between intra- and intermolecular modes are calculated, revealing that the electrical anharmonicity dominates the cross-peak intensities in the 2D Raman-THz response and crystalline, as well as liquid, bromoform. Furthermore, the experimentally observed difference in relative cross-peak intensities between the two intramolecular modes of bromoform and the intermolecular modes can be explained by the C3v-symmetry of bromoform in combination with orientational averaging. The good agreement with the experimental results provides further evidence for our interpretation that the 2D Raman-THz response of bromoform is, indeed, related to the anharmonic coupling between the intra- and intermolecular modes.

Optical properties of the B2O3–CdO–ZnO–Li2O glasses modified with MoO3

Using optical investigations, this report analyzes the impact of MoO3 on lithium zinc cadmium borate glasses. The authors made glasses with the formula 60B2O3–20CdO–10ZnO–(10-x)Li2O–xMoO3 (Where x = 0, 0.5, 1, 1.5 & 2) and the samples were employed to UV–Visible and Electron paramagnetic resonance (EPR) experimental instruments. In order to determine the band gap, refractive index, and Urbach energy, optical absorption spectra are used. With the MoO3 in these glasses, the band gap was lowered while the refractive index improved. High MoO3 concentrations with high refractive indices make these glasses useful for optical applications. Two resonance signals were visible in the EPR spectra, one at g = 4.2 and the other with g = 1.95. The second signal shows that Mo5+ ions have occupied the sites of octahedral coordination with a mild axial distortion and C4V symmetry.

Highly luminescent antiaromatic diborinines with fused thiophene rings.

Tricoordinate boron-incorporated π-conjugated systems are widely investigated as optoelectronic materials because of their unique p-π* orbital interactions and high Lewis acidity. Among them, thiophene-fused diborinines are characterized by moderate antiaromaticity and extended conjugation. In this work, we have developed two new dithienodiborinines with C2h and C2v symmetries, which exhibited completely different optical properties. The thiophene-fused diborinines synthesized in this study showed excellent fluorescence properties both in solution and in the solid state, with quantum yields of up to 95%. The high antiaromaticity enhanced the Lewis acidity of the boron centers, as proven by the large association constants with fluoride ion estimated from titration experiments. The high Lewis acidity and the superior luminescence property have enabled their application as fluorescent sensor materials for the detection of ammonia vapor.

The additional nitrogen atom breaks the uranyl structure: a combined photoelectron spectroscopy and theoretical study of NUO2.

We report a joint photoelectron spectroscopic and relativistic quantum chemistry study on gaseous NUO2-. The electron affinity (EA) of the neutral NUO2 molecule is reported for the first time with a value of 2.602(28) eV. The U-O and U-N stretching vibrational modes for the ground state and the first excited state are observed for NUO2. The geometric and electronic structures of both the anions and the corresponding neutrals are investigated by relativistic quantum chemistry calculations to interpret the photoelectron spectra and to provide insights into the nature of the chemical bonding. Both the ground state of the anion and neutral are calculated to be planar structures with C2v symmetry. Unlike the "T"-shape structure of UO3 which has a quasi-linear O-U-O angle, both the ground-state geometries of the anion and neutral have O-U-O bond angles of around 90°. The significant contraction of the O-U-O bond angle indicates the strong interaction between the U and N atoms compared with the "additional" oxygen in UO3. The chemical bonding calculation indicates that multiple bonding of U(VI) can occur in NUO2- and NUO2, and the UVI-N bond is significantly more covalent than the U-O bond. The current experimental and theoretical results reveal the difference between the U-N and U-O bond in the unified molecular system, and expand our understanding of the bonding capacities of actinide elements with the nitrogen atom.

Photochemical properties of a potential interstellar dust precursor: the electronic spectrum of Si3O2.

Silicon oxide compounds are considered as precursors for silicon-based interstellar dust grains which consist mainly of silica and silicates. Knowledge of their geometric, electronic, optical, and photochemical properties provides crucial input for astrochemical models describing the evolution of dust grains. Herein, we report the optical spectrum of mass-selected Si3O2+ cations recorded in the 234-709 nm range by means of electronic photodissociation (EPD) in a quadrupole/time-of-flight tandem mass spectrometer coupled to a laser vaporization source. The EPD spectrum is observed predominantly in the lowest-energy fragmentation channel corresponding to Si2O+ (loss of SiO), while the higher-energy Si+ channel (loss of Si2O2) provides only a minor contribution. The EPD spectrum exhibits two weaker unresolved bands A and B near 26 490 and 34 250 cm-1 (377.5 and 292 nm) and a strong transition C with a band origin at 36 914 cm-1 (270.9 nm) which shows vibrational fine structure. Analysis of the EPD spectrum is guided by complementary time-dependent density functional theory (TD-DFT) calculations at the UCAM-B3LYP/cc-pVTZ and UB3LYP/cc-pVTZ levels to determine structures, energies, electronic spectra, and fragmentation energies of the lowest-energy isomers. The cyclic global minimum structure with C2v symmetry determined previously by infrared spectroscopy can explain the EPD spectrum well, with assignments of bands A-C to transitions from the 2A1 ground electronic state (D0) into the 4th, 9th, and 11th excited doublet states (D4,9,11), respectively. The vibronic fine structure of band C is analyzed by Franck-Condon simulations, which confirm the isomer assignment. Significantly, the presented EPD spectrum of Si3O2+ corresponds to the first optical spectrum of any polyatomic SinOm+ cation.

Analysis of site symmetries of Er3+ doped CaF2 and BaF2 crystals by high resolution photoluminescence spectroscopy

The understanding of complex relationships between luminescent properties, local symmetry of an emitting center, and the host crystal structure provides a better insight into optical properties of materials. In this work, the alkaline earths CaF2 and BaF2 fluoride crystals doped with 0.1 mol% ErF3 were investigated. The crystals structure has been studied using a synchrotron and laboratory X-ray diffraction. The C3v and C4v sites symmetry were determined using erbium probed high resolution emission spectroscopy (HRPL) at low temperature (LT) of 10 K. The considerable difference in room temperature (RT) optical properties for CaF2 compared to BaF2 crystals was observed. Such difference in absorption intensity of 4.7 times of erbium 4G11/2 manifold in UV, and 7.5 times in green emission from 4S3/2 manifold, could be due to the distinction in the host crystals cationic radius (ΔrCa,Ba) and the dopant-host ionic radius (ΔrCa-Er, ΔrBa-Er). Those Δr differences influence the structure and lead to the following symmetry formation: In CaF2, the C4v and C3v isolated centers were identified, with the determined Er3+- F−i bond lengths of 2.734 Å and 4.735 Å respectively; In BaF2, only C3v isolated centers were identified with the determined Er3+- F−i bond lengths of 5.380 Å. The present work is the first study that takes into account correlations of optical properties, the local symmetry and the structure in mentioned fluorides crystals, and it could be a step forward in the lanthanide doped optical materials systematics.

On the Utility of Ce3+ Spin−Orbit Transitions in the Interpretation of Rate Data in Ceria Catalysis: Theory, Validation, and Application

Cerium oxide is a ubiquitous component in catalytic systems of industrial and academic interest, and the precise mechanistic function of oxygen vacancies/Ce3+ ions a persistent open question in this regard. Existing methods for quantifying vacancy densities are for the most part indirect in nature, and they either have to necessarily be applied ex situ or, if applicable in situ, are oftentimes limited in applicability or quantitative rigor. We present herein a theoretical and experimental analysis of the utility of 2F5/2–2F7/2 electronic transitions in the quantitative estimation of oxygen vacancy or Ce3+ densities. Application of crystal field theory reveals the nonforbidden nature of 2F5/2–2F7/2 transitions for Ce3+ ions present in a C3v site symmetry environment, unlike free Ce3+ ions in the gas phase that exhibit La Porte forbidden transitions between states of equivalent parity. The molar extinction coefficient for the infrared feature of interest is estimated using three reductants─H2, CO, and ethanol─and applied toward interpretation of ceria-catalyzed H2–D2 exchange and tert-butanol dehydration catalysis rate data. Linear correlations between H2–D2 exchange rates and infrared spectroscopy-derived vacancy densities point to the sole involvement of reduced domains in H2 activation steps prevalent in hydrogenation and hydrodeoxygenation catalysis. Contrastingly, areal tert-butanol dehydration rates that trend inversely with vacancy densities both in the presence and absence of α-hydrogen-containing oxygenates carrying a propensity toward stoichiometric oxidative routes suggest the participation of oxidized, not reduced domains in dehydrative turnovers producing isobutene. The nonforbidden nature of the Ce3+2F5/2–2F7/2 transition─evidenced here using symmetry considerations─likely extends beyond the C3v symmetry environment under consideration here, implying that its fortuitous appearance within the infrared region of the electromagnetic spectrum may render it amenable to quantitative application in relating local structure to catalytic function in ceria catalysis more broadly.

Synthesis, Spectroscopic Investigations, Thermal Analysis And DFT Calculations Of Some Pentacarbonyl(Mercaptopyrimidine)Metal(0) Complexes Of Group VI B Elements

Pentacarbonyl-N-mercaptopyrimidinemetal(0) complexes of VIB metals (M: Cr, Mo, W) were formed when hexacarbonylmetal(0) complexes are treated photochemically with 4,6-dimethyl-2-mercaptopyrimidine at 10 ºC. The reported organometallic complexes were purified and isolated under an inert atmosphere. All M(CO)5L complexes were characterized in solution by FTIR-, 1H- and 13C-NMR spectroscopies. The FTIR spectroscopy results showed three absorption bands in the carbonyl region which indicates that the pentacarbonyl metal unit of the complexes has a local C4v symmetry. The 1H- and 13C-NMR spectroscopies showed that the mercaptopyrimidine ligand bonded to the metal complex through the mercaptopyrimidine-nitrogen atom symmetrically. The 13C-NMR spectroscopy results also showed a 1:4 ratio of two peaks in the CO-region, the ratio of the peaks proved the C4v symmetry of these complexes. The thermal behavior of these organometallic complexes is investigated by using DTA/TGA methods. The results of thermal analyses showed that the complexes decomposed at three different temperatures. The density functional theory (DFT) calculations were computed in B3PW91 formalism by Gaussian03W Software. The comparison of the experimental data with the theoretical values showed that the results obtained are compatible with each other. Thus, the accuracy of the experimentally given structural proposal of the obtained organometallic complex compounds was also confirmed through theoretical calculations.

Comparative study of the H and D abstraction in the H + CH3D reaction with a ten-dimensional quantum dynamics model.

The mode selectivity in the prototypical H + CH3D reaction is investigated by the initial state selected time-dependent wave packet method within a ten-dimensional quantum dynamics model. The model is a novel reduced dimensional model for the X + YCZ3 reaction, which allows the CZ3 to break C3V symmetry. The calculated reaction probabilities initially from different reactant vibrational states show that the CH3 stretching modes excitations obviously promote the H-abstraction reaction but have a slight influence on the D-abstraction reaction. In contrast, the CD stretching mode excitation significantly enhances the D-abstraction reaction. For both H- and D-abstraction reactions, the excitation of either the CH3 umbrella bending mode or the CH3 rocking mode shows a promotional effect on the reactivity, while fundamental excitation of the CH3 bending mode has a negligible effect. Impressively, the first-overtone excitation of CH3 bending mode remarkably promotes the H-abstraction reaction, resulting from the 1:2 Fermi coupling between the CH3 symmetric stretching mode and the first overtone of CH3 bending mode. In addition, translational energy is more efficient than vibrational energy in promoting the H-abstraction reaction at low energy, while vibrational energy becomes more efficient for the D-abstraction reaction.

Novel red-emitting orthorhombic GdInO3:Eu3+ perovskite phosphor: Structural resolution, Judd-Ofelt theory, and comparative investigation with hexagonal counterpart

A novel orthorhombic GdInO3:Eu perovskite red phosphor, endowed with good luminescence properties, was synthesized via a facile co-precipitation route plus controllable thermolysis. Its structural features, optical properties, and luminescent behaviors were compared with the hexagonal counterpart in detail. The two GdInO3 matrixes have relatively wide direct bandgaps (∼5.07 eV for orthorhombic perovskite and ∼5.13 eV for hexagonal phase) and low phonon energies (∼368 cm−1 for orthorhombic perovskite and ∼425 cm−1 for hexagonal contrast). Eu3+ substitution for Gd3+ occupies the C2v symmetry site without an inversion center in orthorhombic GdInO3, while the hexagonal GdInO3 provides two crystallographic positions for Eu3+ residence (∼2/3 at C3 site and ∼1/3 at C6v site). The emission spectra of two phosphors present characteristic 5D0→7FJ transitions of Eu3+ and the optimum activator concentrations are both 10 at.%. They also have good thermal stability of luminescence with relatively high similar activation energies of ∼0.25 eV. F+ center (VO∙ oxygen vacancy) is the primary defect form in the two perovskites, which has little effect on the entire red emission of orthorhombic phosphor but shifts the chromaticity coordinate of hexagonal contrast toward orange region. The orthorhombic GdInO3:Eu phosphor exhibits stronger emission intensity, a longer fluorescence lifetime, and a higher color purity than the hexagonal counterpart. Judd–Ofelt theory further confirms that orthorhombic GdInO3:Eu is an efficient red-emitting material with the relatively large parameters of Ω2 = 7.01 × 10–20 cm–2 and Ω4 = 2.85 × 10–20 cm–2.

Tb3+ Ion Optical and Magneto-Optical Properties in the Cubic Crystals KTb3F10.

The optical and magneto-optical characteristics of KTb3F10 crystals in the transition region of 5D4 → 7F6 4f8 configurations of the Tb3+ ion at temperatures of 90 and 300 K were studied. The schemes of the optical transitions in the KTb3F10 crystals were constructed, and the energies of most of the Stark sublevels of the ground 7F6 and excited 5D4 multiplets of the Tb3+ ion split by the C4v symmetry crystal environment were determined. The presence of three- and two-doublet states in the energy spectra of the Tb3+ion multiplets 7F6 and 5D4, respectively, was established, which is in good agreement with theoretical predictions. The use of the wavefunctions of the Stark sublevels of multiplets split by a tetragonal crystal field and combining in the studied optical transition made it possible to explain some of the magnetic and magneto-optical features observed in the KTb3F10 single crystals.

Monometallic Endohedral Azafullerene.

Azafullerenes derived from nitrogen substitution of carbon cage atoms render direct modifications of the cage skeleton, electronic, and physicochemical properties of fullerene. Gas-phase ionized monometallic endohedral azafullerene (MEAF) [La@C81N]+ formed via fragmentation of a La@C82 monoadduct was detected in 1999, but the pristine MEAF has never been synthesized. Here, we report the synthesis, isolation, and characterization of the first pristine MEAF La@C81N, tackling the two-decade challenge. Single-crystal X-ray diffraction study reveals that La@C81N has an 82-atom cage with a pseudo C3v(8) symmetry. According to DFT computations, the nitrogen substitution site within the C82 cage is proposed to locate at a hexagon/hexagon/pentagon junction far away from the encapsulated La atom. La@C81N exists in stable monomer form with a closed-shell electronic state, which is drastically different from the open-shell electronic state of the original La@C82. Our breakthrough in synthesizing a new type of azafullerene offers a new insight into the skeletal modification of fullerenes.

Valley Hall elastic topological insulator with large Chern numbers

We present a reconfigurable electro-elastic topological insulator that produces a new valley phase with a large Chern number. This piezoelectric metamaterial comprises a hexagon-like honeycomb structure and periodic bonded piezoelectric beams. The composite piezoelectric Mindlin plate formulation in the isogeometric analysis is employed to calculate the band structure. A Dirac cone can emerge at the K point due to the C3v symmetry of the primitive element. Nontrivial topologically protected bandgaps develop after breaking mirror symmetry with the adding-on negative capacitance circuit. Additionally, we demonstrate that the topological quantity in this system arises in a large valley Chern number of one. The domain wall will exhibit two edge states between different topological microstructures according to the bulk-edge correspondence principle. The shielded transport of flexural waves is highly resistant to structural disturbances such as sharp corners or cavity flaws in the proposed metamaterial, resulting in a novel strategy for the reconfigurable electro-elastic topological insulator.

Synthesis, crystal structure, electronic structure, and intensive zero-phonon-line emission of Mn4+ in K5Nb3OF18 lattice

Manganese ions-activated fluorides and oxyfluorides have found applications in solid state lighting and display, but the coordination environments of Mn4+ activator and their effects on the photoluminescence (PL) properties in some host lattices have remained unclear. In this study, microcrystal powders of oxyfluoride K5Nb3OF18 with and without Mn4+-doped were synthesized by using a coprecipitation method. The morphology, crystal structure, electronic structure of K5Nb3OF18 and the coordination environments and PL properties of Mn4+ activator in K5Nb3OF18:Mn4+ were investigated. It is revealed that K5Nb3OF18 crystallizes in the tetragonal structure with the space group I4cm. There are two crystallographic sites for Nb5+ ions in the lattice, both of which have C4v symmetry. Mn4+ ions-activated K5Nb3OF18 shows characteristic emission due to the transition from 2E to 4A2, while with intensive zero-phonon-line (ZPL). Structure analysis indicates that the local environments of Nb5+ ions in K5Nb3OF18 are more contracted and distorted than those in Rb5Nb3OF18. These features along with the non-centrosymmetric nature of the Nb5+ sites are considered to response for the intensive ZPL emission.

Front Cover: Symmetry‐Protected Two‐Level System in the H3 Center Enabled by a Spin–Photon Interface: A Competitive Qubit Candidate for the NISQ Technology (Adv. Quantum Technol. 11/2022)

Investigation of promising spin-qubit candidates in solid materials is vital for scalable noisy intermediate scale quantum (NISQ) technologies. As demonstrated by Hailong Wang, Heng Yuan, and colleagues in article number 2200044, a symmetry-protected two-level system (qubit) based on the H3 center in diamond with C2v symmetry is characterized, which is capable of applications in quantum information processing. The figure depicts an N–V–N geometry (H3 center) in the diamond acting as a spin–photon interface, which can interrogate the spin information of the qubit in the form of fluorescence. The green beam is fluorescence, the oscillation at the bottom represents the evolution of spin states, and the surrounding “0” and “1” elements indicate that this work provides a very competitive processor for quantum computing.

Defining shapes of two-dimensional crystals with undefinable edge energies

The equilibrium shape of crystals is a fundamental property of both aesthetic appeal and practical importance: the shape and its facets control the catalytic, light-emitting, sensing, magnetic and plasmonic behaviors. It is also a visible macro-manifestation of the underlying atomic-scale forces and chemical makeup, most conspicuous in two-dimensional (2D) materials of keen current interest. If the crystal surface/edge energy is known for different directions, its shape can be obtained by the geometric Wulff construction, a tenet of crystal physics; however, if symmetry is lacking, the crystal edge energy cannot be defined or calculated and thus its shape becomes elusive, presenting an insurmountable problem for theory. Here we show how one can proceed with auxiliary edge energies towards a constructive prediction, through well-planned computations, of a unique crystal shape. We demonstrate it for challenging materials such as SnSe, which is of C2v symmetry, and even AgNO2 of C1, which has no symmetry at all.

Elastic Electron Scattering by Diborane(6) and Diborane(4) Molecules

We present integral, differential, and momentum transfer cross sections for elastic electron collisions with the two most stable isomers of the B2H4 molecule, hereafter referred to as isomer I (C2v symmetry) and isomer II (D2d symmetry), and with the B2H6 molecule (D2h symmetry). The isomer I of B2H4 and the B2H6 molecule are known for their electrodeficiency in the "three-center two-electron" (3c-2e) bond, a region in which a hydrogen atom occupies a bridged position between two non-hydrogen atoms. The cross sections were computed by using the Schwinger multichannel method implemented with norm-conserving pseudopotentials, and the scattering calculations were carried out in the static-exchange and static-exchange plus polarization levels of approximation for energies from 0.1 to 50 eV. We discuss the presence of shape resonances in the scattering cross sections. We also made a direct comparison among the cross sections of these three targets.

Symmetry‐Protected Two‐Level System in the H3 Center Enabled by a Spin–Photon Interface: A Competitive Qubit Candidate for the NISQ Technology

AbstractRecent technological advances in the noisy intermediate‐scale quantum (NISQ) era are promising. Optically addressable color centers in semiconductors can achieve spin localization and are the most promising spin qubit candidates for NISQ technologies. Exploring a suitable and scalable atomic‐like color center is a prerequisite in this context. Here, a symmetry‐protected two‐level system (qubit) derived from a set of naturally separated Bell states in the H3 center with C2v symmetry is characterized. The characterized qubit significantly reduces magnetic noise compared with a degenerate triplet in C3v systems for conventional qubits. The Hamiltonian, including the Coulomb interaction, spin–orbit coupling, and spin–spin interaction, is comprehensively developed using a combination of first‐principle calculations and group theory analyses. Consequently, an intrinsic spin–phonon interface embedded in an optical spin‐polarization loop can enable an effective interrogation of the information of the two‐level system. This study not only paves the way for developing further quantum information science applications utilizing the H3 center but also provides a competitive qubit candidate for the NISQ era.

Synthesis of a Hexachloro Sulfate(IV) Dianion Enabled by Polychloride Chemistry.

The preparation and structural characterization of [NEt3 Me]2 [SCl6 ] is described, which is the first example of a [SCl6 ]2- dianion and of a halosulfate anion of the type [Sx Xy ]z- in general. This dianion belongs to the group of 14-valence electron AB6 E systems and forms an octahedral structure in the solid-state. Interestingly, co-crystallization with CH2 Cl2 affords [NEt3 Me]2 [SCl6 ]⋅4 CH2 Cl2 containing [SCl6 ]2- dianions with C4v symmetry. As suggested by quantum-chemical calculations, the distortion of the structure is not caused by a stereochemically active lone pair but by enhanced hydrogen bonding interactions with CH2 Cl2 . At elevated temperatures, [NEt3 Me]2 [SCl6 ] decomposes to various sulfur chlorine compounds as shown by Raman spectroscopy. Cooling back to room temperature results in the selective formation of [NEt3 Me]2 [SCl6 ] which is comparable to the well-studied SCl4 .

Observation of Two-dimensional Isotropic Double Dirac Cones in the Electromagnetic Dispersion Relation

We report on the first experimental observation of two-dimensional isotropic double Dirac cones in the electromagnetic dispersion relation, which were materialized by the accidental degeneracy of E1- and E2-symmetric eigenmodes on the Γ point of photonic crystals. We fabricated triangular-lattice photonic crystal slabs of the C6v symmetry on silicon-on-insulator wafers by electron beam lithography and examined their dispersion relation by high-resolution angle-resolved reflection spectroscopy in the mid-infrared range. We observed the characteristic linear dispersion of the double Dirac cones together with the polarization selection rules derived from the mode symmetries. All these observations agreed with numerical calculation of the dispersion relation and reflection spectra by the finite element method.