Electronic State of Hydroxyl-terminated Dimeric Titanium Structure

Geometries and energy separations of the various low-lying electronic states of Rh3+, Rh4+, and Rh5+ clusters with different structural arrangements have been investigated. The complete active space multiconfiguration self-consistent field method, (CASMCSCF) followed by large scale multireference singles plus doubles configuration interaction (MRSDCI) computations that included up to 1.6 million configurations for Rh3+, 1.5 million configurations for Rh4+, and 2.7 million configurations for Rh5+, were used. Four nearly degenerate electronic states were found for Rh3+. The A′6 electronic state of the pyramidal structure of Rh4+ was found to be the ground state. Although the A″6 electronic state of Rh4+ with the same geometry was found to be close in energy at the CASMCSCF level, it is 0.5 eV higher at the higher level of theory. Two nearly degenerate electronic states (A″5 and A″5) of the distorted edge capped tetrahedron structure of Rh5+ were found as candidates for the ground state of this cluster. Mulliken population analysis has been carried out on these cationic clusters to investigate their bonding properties.

The dimer of dimethyl tetrazine (DMT)2 has been prepared in a supersonic free jet and its structure and dynamics have been studied by laser induced fluorescence spectroscopy. The binding energy of the excited π*←n electronic state of the dimer was significantly greater than the binding energy of the ground electronic state, and we have called the DMT dimer a mild excimer. The geometry of the DMT dimer was determined from the analysis of the rotational structure in the spectrum of the perdeutero isotopic species and was found to have the two DMT rings stacked and parallel with one ring slipped with respect to the other. At our lowest temperature the perdeutero species was found to have nonrotating methyl groups while the h12 isotopic species had freely rotating methyl groups at all temperatures. The structure of the DMT dimer was consistent with the observation of two exposed aromatic faces as determined by the observation of two van der Waals molecules formed by binding one or two helium atoms to the dimer. When excited vibrational levels of the excited electronic state were pumped, the emission spectrum was dominated by emission from levels reached by intramolecular vibrational relaxation of the initially excited level. The rate of intramolecular vibrational relaxation out of the 6a1 level was found to be 17±6×109 s−1 as determined from the line broadening observed in the fluorescence excitation spectrum. Emission from electronically excited monomers produced by photodissociation of the DMT dimer was observed, but relaxation was always the dominant process and appeared to be much faster than photodissociation.

The low energy electronic structure of the copper dimer has been re-investigated using non-linear four-wave mixing spectroscopy and high level ab initio calculations. In addition to the measurement of the previously reported A, B, and C electronic states, a new state denoted A' is identified with T0 = 20 100.4090(16) cm-1 (63Cu2). Rotational analysis of the A'-X (0,0) and (1,0) transitions leads to the assignment of A' 1u. Ab initio calculations present the first theoretical description of the low energy states of the copper dimer in Hund's case (c) and confirm the experimental assignment. The discovery of this new low energy excited state emphasizes that spin-orbit coupling is significant in states with d-hole electronic configurations and resolves a decades-long mystery in the initial assignment of the A state.

Surfaces of semiconductors are crucially important for electronics, especially when the devices are reduced to the nanoscale. However, surface structures are often elusive, impeding greatly the engineering of devices. Here we develop an efficient method that can automatically explore the surface structures using structure swarm intelligence. Its application to a simple diamond (100) surface reveals an unexpected surface reconstruction featuring self-assembled carbon nanotubes arrays. Such a surface is energetically competitive with the known dimer structure under normal conditions, but it becomes more favourable under a small compressive strain or at high temperatures. The intriguing covalent bonding between neighbouring tubes creates a unique feature of carrier kinetics (that is, one dimensionality of hole states, while two dimensionality of electron states) that could lead to novel design of superior electronics. Our findings highlight that the surface plays vital roles in the fabrication of nanodevices by being a functional part of them.

A two-site Hubbard model has been utilized for description of the electron - molecular vibration coupling (EMVC) in organic charge-transfer (CT) salts with dimerized structures. It was shown that the intermolecular charge oscillations in the anti-phase totally symmetric vibrations are accompanied by a decrease of energy of the occupied electronic state in the dimer. This effect is responsible for the frequency shift of i.r.-active electron-vibrational bands compared with relevant Raman modes, and can be described in terms of dimensionless coupling constants. The absorption coefficients for the bands were found to be proportional to the frequency shifts. The calculated values are in good quantitative agreement with experimental data for BEDT-TTF-based and TTF-based monovalent CT complexes. .

Photoinduced intramolecular proton transfer represents a chemical reaction that has mainly been studied in electronically excited molecules. For benzothiazole and -triazole compounds, recent femtosecond experiments gave evidence of excited state proton and deuterium transfer on a time scale of 100 to 200 fs [1,2]. In 2-(2’-hydroxy-5’-methylphenyl)- benzotriazole (trade name: TINUVIN P, TIN), the excited state enol→keto reaction (see structures (I) and (II)) is followed by the radiationless relaxation to the ground state of the keto-type molecules, occurring with a time constant of 150 fs. This species eventually undergoes a proton back-transfer to the ground state of the original enol structure. Until now, there was little information on the ground state reaction of TIN and of other compounds undergoing a closed reaction cycle. In particular, vibrational redistribution processes randomizing the large amount of energy from the initial photoexcitation (≃ 4 eV) have not been observed. In this paper, we discuss the first study of those processes with a time resolution of 100 fs, directly revealing the subpicosecond proton transfer in the ground state of TIN and the strong vibrational heating of the reaction product.

Recently, studies of solar cells have been conducted actively. Especially, organic thin film solar cells are attracting attention for use as a next-generation flexible substrate material. The reasons include the recent advent of bulk heterojunction structures. Nevertheless, bulk heterojunction solar cells exhibit only about 10% conversion efficiency. They have remained in the study phase. One reason for their low conversion efficiency is that a bulk heterojunction conductive mechanism is so complicated that its fundamental electronic properties have not been elucidated well. This letter describes an examination of the excited state of the bulk heterojunction structure and evaluates its electronic properties. Charge densities are computed for excited and ground states. Then absorbance is computed and examined. Results suggest that the electronically excited state might come to differ from the electronic ground state in a phthalocyanine–fullerene bimolecular system. Moreover, we infer that this behavior brings about energy level change and subsequent variation in absorbance.

The atomic precision of sub-nanometer-sized metal nanoclusters makes it possible to elucidate the kinetics of metal nanomaterials from the molecular level. Herein, the size reduction of an atomically precise [Au23(CHT)16]- (HCHT = cyclohexanethiol) cluster upon ligand exchange with HSAdm (1-adamantanethiol) has been reported. During the 16 h conversion of [Au23(CHT)16]- to Au16(SR)12, the neutral 6e Au21(SR)15, and its 1e-reduction state, i.e. the 5e, cationic radical, [Au21(SR)15]+, are active intermediates to account for the formation of thermodynamically stable Au16 products. The combination of spectroscopic monitoring (with UV-vis and ESI-MS) and DFT calculations indicates the preferential size-reduction on the corner Au atoms on the core surface and the terminal Au atoms on longer AunSn+1 staples. This study provides a reassessment on the electronic state of the Au21 structure and highlights the single electron transfer processes in cluster systems and thus the importance of the EPR analysis on the mechanistic issues.

Electronic states of Ta 2C +

The optical analysis of multilayer structures formed from the topmost layer of InGaAs/GaAs quantum rings (QRs) grown on a vertically stacked and laterally aligned InGaAs/GaAs quantum dot (QD) superlattice has been performed to elucidate the nature of the contribution from each layer. These hybrid structures representing a coupled QR chain layer and the layers of self-assembled QD chains display strong optical anisotropy. Unusually strong oscillations are observed in the circularly polarized photoluminescence (PL) intensities under magnetic field for emissions in the spectral range of the QD structure and these oscillations occur simultaneously with weaker oscillations related to the Aharonov-Bohm interference that modulates the emissions from the QR top layer of the structure. The behavior seen in the magneto-PL spectrum is interpreted in terms of joint effects associated to strain, spatial, and magnetic field confinements on the valence band states forming the magnetoexciton ground state of this multilayered structure. The result can be ascribed to a magnetically induced dark exciton contribution where the heavy-hole (type II) state becomes localized outside, whereas light-hole (type I) as well as electron states remain inside the spatial confinement area of the QD.

The first-principles LDA calculation is applied to the electronic states of Si(100) reconstructed surfaces. Among various higher order reconstruction structures of asymmetric dimers, c(4 × 2) structure is found to be the most stable structure. The firstprinciples molecular dynamics calculation provided a supporting evidence for the stability of asymmetric dimer structure. The energy band of the c(4 × 2) surface reveals the semiconducting surface band dispersion, which gives an excellent agreement with the ARUPS result for the single domain surface. The stabilization mechanism of the c(4 × 2) surface is ascribed to the hybridization interaction between the orbitale of the up dimer atoms in the adjacent row, and not to the ionic interaction as p(2 × 2) structure. The theoretical simulation of STM/STS on the Si(100) surfaces explained fairly well the experimental feature. The ‘seemingly symmetric’ dimer in the STM image does not necessarily correspond to the real symmetric dimer.

Our results clarified uniqueness in hydrogen bonding TTFPy dimer in which proton in hydrogen bond was thermally fluctuated. In addition, the fluctuation was coupled with π-electronic systems of TTF moiety where electric dipole moment was amplified.

Applied static pressure can largely modify the structure and dynamics of molecular systems, with consequences on their optical properties and chemical stability. When photochemical effects are exploited in conjunction with the structural and dynamical conditions attained at high density, chemical reactivity may become highly selective and efficient, yielding technologically attractive products. Non-linear optical spectroscopies are a powerful tool to investigate molecular energetics and dynamics, and thus unveil key aspects of the chemical reactivity at a molecular level. Their application to high-pressure samples is experimentally challenging, mainly because of the small sample dimensions and the non-linear effects generated in the anvil materials. In this paper we review the main results on the behavior of electronic states at high pressure, obtained by non-linear optical techniques, discussing the relationship between pressure-induced structural modifications and chemical reactivity, and the state of the art of ongoing research.

Molecular structure, vibrational investigation of 2-chloro-α-α-α-trifluoro-3,5-dinitrotoluene using DFT (LSDA, B3LYP, B3PW91 and MPW1PW91) and UV–Vis absorption spectra in organic solvents: A IEF-PCM/TD-DFT study

Bis(2-(2-hydroxyphenyl)benzothiazolate)zinc (Zn(BTZ)(2)) is one of the best white electroluminescent materials used in organic light-emitting diodes (LEDs). Despite a large number of studies devoted to this complex, very little is known about its basic molecular and electronic structures and electron transport properties in LEDs. Therefore, we investigate the structures and electroluminescent properties. The unsolvated single crystal of Zn(BTZ)(2) was grown and its crystalline structure was determined from X-ray diffraction data. The crystal is triclinic, space group P-1, a = 9.4890(19) A, b = 9.5687(19) A, c = 11.685(2) A, alpha = 84.38(3) degrees, beta = 78.94(3) degrees, gamma = 83.32(3) degrees. The structure of the chelate is dimeric [Zn(BTZ)(2)](2) with two isotropic Zn(2+) ion centers having five-coordinate geometry. The present study provides direct evidence for the sole existence of dimeric structure in the powder and the thin film. The dimer is energetically more stable than the monomer. Analysis of the electronic structure of [Zn(BTZ)(2)](2) calculated by density functional theory reveals a localization of orbital and the distribution of four orbital "tetrads". The structural stabilities of both anion and cation and the distribution of the hole in the cation and that of the excess electron in the anion are discussed in terms of theoretical calculations. Strong intermolecular interaction may be expected to enable good electron transport properties as compared with tris(8-hydroxyquinolinato)aluminum.