Spectroscopy of XY3Z (C3v) molecules: A tensorial formalism adapted to the O (3) ⊃ C∞v ⊃ C3v group chain

A tensorial formalism adapted to the case of XY₃Z symmetric tops has been developed. We use the O (3) ⊃ C_∞v ⊃ C_3v group chain. All the coupling coefficients and formulas for the computation of the matrix elements are given for this chain. Such relations are also deduced in C_3v group itself.     

Tensorial development of the rovibronic Hamiltonian and dipole moment operators for XY3Z molecules with a degenerate electronic state: Preliminary application to the CH3O radical

We present a development of the Hamiltonian and transition moment operators of XY₃Z (C_3v) symmetric tops molecules in a degenerate electronic state with the aid of a tensorial formalism developed in a recent paper [A. El Hilali, V. Boudon, M. Loëte, J. Mol. Spectrosc. 239 (2006) 41-50]. Electronic operators are defined from group theory properties. They provide a new approach to build an effective rovibronic Hamiltonian as well as an effective dipole moment operator for rovibronic transition of XY₃Z molecules. This model is studied qualitatively thanks to the tensorial algebra properties. Expressions of the matrix elements are derived for these operators. A first simple application to the ground electronic state of CH₃O is proposed as an illustrative example.     

Vibrational assignment of isoxazole aided by rovibrational data and density functional theory

IR and Raman spectra of isoxazole and D₃-isoxazole are reassigned with the aid of density functional theory calculations at the B3LYP/6-311+G(d,p) level. Harmonic wavenumber values of all non-CH stretch modes give an r.m.s. deviation from experimental values of 3 cm⁻¹ when they are uniformly scaled by 0.9818. Anharmonic values obtained using a second-order perturbative approach show an r.m.s. deviation of 7.6 cm⁻¹. Results of equal quality are obtained for D₃-isoxazole. Predicted Raman and IR band strengths match experimental spectra very closely. Detailed re-examination of rovibrational constants and inertial defect data from high resolution IR spectra, in comparison with values from the anharmonic frequency calculation, provides confirmation of the vibrational assignments. ‘Dark state’ fundamentals ν₁₂ (900.2 cm⁻¹) and ν₁₅ (866 cm⁻¹) are detected through the perturbations they cause in nearby bands.     

Projector formalism of generalized Brownian motion theory applied to dissipative and noisy systems

The projector formalism of Zwanzig-Mori type is extended to obtain generalized Fokker-Planck and generalized nonlinear Langevin equations for coarse-grained variables when the underlying microscopic dynamics is dissipative and noisy (stochastic).     

Spectroscopy of X2Y4 (D2h) molecules: tensorial formalism adapted to the O(3)⊃D2h chain, Hamiltonian and transition moment operators

A tensorial formalism adapted to the case of the X₂Y₄ molecules with D_2h symmetry has been developed in the same way as in the previous works on XY₄ (T_d) and XY₆ (O_h) spherical tops and XY₅Z (C_4v) symmetric tops. Here, we use the O(3)⊃D_2h group chain. All the coupling coefficients and formulas for the computation of matrix elements are given for this chain and used in the case of the Hamiltonian and transition moment operators.     

Combined analysis of the high sensitivity Fourier transform and ICLAS-VeCSEL absorption spectra of D2O between 8800 and 9520 cm

The absorption spectrum of dideuterated water, D₂O, has been recorded between 8800 and 9520 cm⁻¹ by intracavity laser absorption spectroscopy (ICLAS) based on a vertical external cavity system emitting laser (VeCSEL) and by high sensitivity Fourier Transform spectroscopy. The combined analysis of the spectra has allowed attributing 1223 transitions to the D₂O species. The spectrum assignment was performed on the basis of the recent results of variational calculations based on an optimized potential energy surface of D₂O. A set of 687 energy levels was derived from transitions assigned to eight upper vibrational states, 577 of them being reported for the first time. A detailed line list has been generated. The line intensities were retrieved mainly from the FTS spectrum and the absolute integrated intensities of the 2v₁ + v₂ + v₃ and the v₂ + 3v₃ bands dominating the spectrum have been determined.     

Development of the Hamiltonian and transition moment operators of symmetric top molecules using the O (3) ⊃ C∞v ⊃ C3v group chain

We present a development of the Hamiltonian, dipole moment, and polarizability operators for XY₃Z molecules. These rovibrational operators are written with the aid of a tensorial formalism derived from the one already used in Dijon and adapted to the XY₃Z symmetric tops in a recent paper [A. El Hilali, V. Boudon, M. Loëte, J. Mol. Spectrosc. 234 (2005) 166-174]. We use the O (3) ⊃ C_∞v ⊃ C_3v group chain. Expressions for the matrix elements are derived for these operators.     

Classification of quantum phases and topology of logical operators in an exactly solved model of quantum codes

Searches for possible new quantum phases and classifications of quantum phases have been central problems in physics. Yet, they are indeed challenging problems due to the computational difficulties in analyzing quantum many-body systems and the lack of a general framework for classifications. While frustration-free Hamiltonians, which appear as fixed point Hamiltonians of renormalization group transformations, may serve as representatives of quantum phases, it is still difficult to analyze and classify quantum phases of arbitrary frustration-free Hamiltonians exhaustively. Here, we address these problems by sharpening our considerations to a certain subclass of frustration-free Hamiltonians, called stabilizer Hamiltonians, which have been actively studied in quantum information science. We propose a model of frustration-free Hamiltonians which covers a large class of physically realistic stabilizer Hamiltonians, constrained to only three physical conditions; the locality of interaction terms, translation symmetries and scale symmetries, meaning that the number of ground states does not grow with the system size. We show that quantum phases arising in two-dimensional models can be classified exactly through certain quantum coding theoretical operators, called logical operators, by proving that two models with topologically distinct shapes of logical operators are always separated by quantum phase transitions.     

General criterion to discern between coherent and incoherent synthesis of broadband coherent anti‐Stokes Raman spectra

Recently, the ordinary qualitative criterion on how to distinguish between coherent and incoherent convolutions of broadband coherent anti‐Stokes Raman (CARS) signals generated by degenerate pump lasers has been revised in view of a quantitative analysis. The revision has established that incoherent CARS approach can be justified as unitary limit of the function ] erfc(Γ/σ₁)/σ₁, where Γ and σ₁ are respectively the spectral widths of the Raman line and the degenerate pump lasers. The result was, however, limited to nonoverlapping Raman lines. In this work, the extension to a more common situation of closely spaced Raman transitions is considered. For large overlap between adjacent Raman lines, the new analysis suggests significant deviations from the previous result. Weak line mixing is also taken into consideration. Nonetheless, all types of deviations are characterized by a common tendency toward the incoherent limit. Copyright © 2007 John Wiley & Sons, Ltd.     

A 57Fe Mössbauer characterization of Fe-biopolymer complexes and their relevance to biological molecules

⁵⁷Fe Mössbauer spectroscopy is used to study the interactions, geometry, and the coordination characteristics of the Fe-complexes of biopolymers such as chitosan, glucosamine, and chondritin sulfate. In addition, a computational effort is undertaken for predicting the geometries and energies of the metal complexes by the Density Functional Theory (DFT) methods as implemented in the Gaussian 2003 quantum mechanical program. Both experimental and computational results suggest that the structure of the metal complexes resemble closely the structure of the active sites of metalloenzymes in 2+ or 3+ oxidation states and is at least tetracoordinated and can possibly have six ligands.     

A simple and accurate approach for calculating the vibration spectra of molecules on surfaces: Comparisons to high resolution electron energy loss data for ethylene on silicon

Peak assignment is a complex but important task for analyzing the vibration spectra of surface-bound molecules. Here we describe a simple approach for calculating infrared and Raman spectra for surface-bound molecules using a cluster model approach with quantum capping potentials (QCPs). The utility of the approach is demonstrated by comparisons to the measured high resolution electron energy loss spectra for ethylene on clean silicon. By capping the silicon cluster with QCPs we computed spectra that agree very well with the HREEL spectrum, allowing us to easily assign the experimental peaks. QCPs are similar to effective core potentials, can be used with any ab initio technique and most computational chemistry packages, and their use requires no special expertise.     

Structures,energetics and vibrational spectra of (H2O)32 clusters: a journey from model potentials to correlated theory

Empirical model potentials are found to be very useful for generating most competitive minima of large water clusters, whereas correlated (e.g. second order-Møller–Plesset perturbation (MP2) theory or higher) calculations are necessary for predicting their accurate energetics and vibrational features. The present study reports the structures and energetics of (H₂O)₃₂ clusters at MP2 level using aug-cc-pvDZ basis set, starting with low-lying structures generated from model potentials. Such high-end and accurate calculations are made feasible by the cost-effective fragment-based molecular tailoring approach (MTA) in conjunction with the grafting procedure. The latter is found to yield electronic energies with a sub-millihartree accuracy with reference to their full calculation counterparts. The vibrational spectra of nine low-lying (H₂O)₃₂ isomers are obtained from the corresponding MTA-based Hessian matrix. All these low-lying isomers show almost similar spectral features, which are in fair agreement with the experiment. The experimental spectrum of (H₂O)₃₂ is thus better understood from the vibrational features of this set of very closely spaced isomers. The present case study of (H₂O)₃₂ clearly demonstrates the efficacy in obtaining accurate structures, energetics and spectra at correlated level of theory by combining model potential-based structures with fragmentation methods.     

常温及常压至1.2GPa条件下异辛烷的拉曼光谱研究

利用碳化硅压腔在室温(25℃)下,研究了异辛烷(2,2,4-三甲基戊烷)在常压至1.2GPa条件下的拉曼光谱特征。研究结果表明,异辛烷CH2和CH3的碳氢伸缩振动的拉曼位移随着压力的增大均呈线性向高频方向移动,其拉曼位移与压力的函数关系为:ν2 873=0.002 8P+2 873.3;ν2 905=0.004 8P+2 905.4;ν2 935=0.002 7P+2 935.0;ν2 960=0.012P+2 960.9。在1.0GPa附近,异辛烷的拉曼位移出现突变,与显微镜下观察发生的异辛烷液-固相变一致。结合异辛烷在常压下的熔点数据,获得了异辛烷的液-固两相相图,并根据克拉贝龙方程获得了液-固相转变过程中的摩尔体积变化量ΔVm=4.46×10-6 m3.mol-1和熵变ΔS=-30.32J.K-1.mol-1。     

DFT calculations of XPS/NEXAFS and IR spectra to elucidate the reaction products of acetonitrile with Si(0 0 1)-2 × 1

NEXAFS data [S. Rangan et al., Phys. Rev. B 71 (2005) 165319] and FTIR data [M.P. Schwartz, R.J. Hamers, Surf. Sci. 601 (2007) 945] apparently do not converge in the identification of the reaction products of acetonitrile (CH₃CN) with Si(0 0 1)-2 × 1 at room temperature. Using DFT calculations of core-excited/core-ionized spectra and of IR vibrational frequencies and intensities, we show the consistency of the body of experimental data. Three species are present on the surface in equivalent amounts, a CN moiety, a pendent CN and a CCN ketenimine submitted to a strong twist imposed by the Si bond directionality. More generally, the paper shows the usefulness of spectroscopic data simulations in the elucidation of complex surface chemistry problems.     

Surface chemistry and catalysis of oxide model catalysts from single crystals to nanocrystals

Fundamental understandings of surface chemistry and catalysis of solid catalysts are of great importance for the developments of efficient catalysts and corresponding catalytic processes, but have been remaining as a challenge due to the complex nature of heterogeneous catalysis. Model catalysts approach based on catalytic materials with uniform and well-defined surface structures is an effective strategy. Single crystals-based model catalysts have been successfully used for surface chemistry studies of solid catalysts, but encounter the so-called “materials gap” and “pressure gap” when applied for catalysis studies of solid catalysts. Recently catalytic nanocrystals with uniform and well-defined surface structures have emerged as a novel type of model catalysts whose surface chemistry and catalysis can be studied under the same operational reaction condition as working powder catalysts, and they are recognized as a novel type of model catalysts that can bridge the “materials gap” and “pressure gap” between single crystals-based model catalysts and powder catalysts. Herein we review recent progress of surface chemistry and catalysis of important oxide catalysts including CeO₂, TiO₂ and Cu₂O acquired by model catalysts from single crystals to nanocrystals with an aim at summarizing the commonalities and discussing the differences among model catalysts with complexities at different levels. Firstly, the complex nature of surface chemistry and catalysis of solid catalysts is briefly introduced. In the following sections, the model catalysts approach is described and surface chemistry and catalysis of CeO₂, TiO₂ and Cu₂O single crystal and nanocrystal model catalysts are reviewed. Finally, concluding remarks and future prospects are given on a comprehensive approach of model catalysts from single crystals to nanocrystals for the investigations of surface chemistry and catalysis of powder catalysts approaching the working conditions as closely as possible.     

Orientation of O(3) and SU(2)⊗CI representations in cubic point groups (Oh,Td) for application to molecular spectroscopy

We propose a detailed method for the symmetrization of the standard O(3) or SU(2)⊗C_I basis |j_τ,m〉 (τ=g or u) into the O_h or T_d point group. This is realized by means of an orientation matrix called G. The oriented basis obtained in this way allows matrix element calculations for rovibronic spectroscopic problems concerning octahedral or tetrahedral molecules. Particular attention has been put on careful phase choices. A numerical calculation of all the G matrix elements for both integer and half-integer j values up to 399/2 has been performed. Such high angular momentum values are necessary for the case of heavy molecules with high rotational excitation. To calculate the G coefficients with high precision at high j values we pre-calculated the necessary Wigner functions using symbolic MAPLE software and made then the numerical calculations with quadruple precision. The complete list of these coefficients can be obtained freely at the URL: http://www.u-bourgogne.fr/LPUB/group.html. As an illustration, we also present briefly an application to two typical spectroscopic calculations: the pure rotational levels of SF₆ in its ground vibrational state and the ν₃ band of ReF₆ (an open-shell molecule with an odd number of electrons and a fourfold degenerate electronic ground state).     

New massively parallel linear-response coupled-cluster module in ACES III: application to static polarisabilities of closed-shell molecules and oligomers and of open-shell radicals

ABSTRACT

Stemming from our implementation of parallel coupled-cluster (CC) capabilities for electron spin resonance properties [J. Chem. Phys. 139, 174103 (2013)], we present a new massively parallel linear response CC module within ACES III. Unlike alternative parallel CC modules, this general purpose module evaluates any type of first- and second-order CC properties of both closed- and open-shell molecules employing restricted, unrestricted and restricted-open-shell Hartree–Fock (HF) references. We demonstrate the accuracy and usefulness of this module through the calculation of static polarisabilities of large molecules. Closed-shell calculations are performed at the following levels: second-order many-body perturbation theory [MBPT(2)], CC with single- and double-excitations (CCSD), coupled-perturbed HF and density functional theory (DFT), and open-shell calculations at the unrestricted CCSD (UCSSD) one. Applications involve eight closed-shell organic-chemistry molecules (Set I), the first four members of the closed-shell thiophene oligomer series (Set II), and five open-shell radicals (Set III). In Set I, all calculated average polarisabilities agree reasonably well with experimental data. In Set II, all calculated average polarisabilities vs. the number of monomers show comparable values and saturation patterns and demonstrate that experimental polarisabilities may be inaccurate. In Set III, UCCSD perpendicular polarisabilities show a reasonable agreement with previous UCCSD(T) and restricted-open-shell-MBPT(2) values.     

Measurements of NO2 mixing ratios with topographic target light scattering-differential optical absorption spectroscopy system and comparisons to point monitoring technique

A topographic target light scattering-differential optical absorption spectroscopy(ToTaL-DOAS) system is developed for measuring average concentrations along a known optical path and studying surface-near distributions of atmospheric trace gases.The telescope of the ToTaL-DOAS system points to targets which are located at known distances from the measurement device and illuminated by sunlight.Average concentrations with high spatial resolution can be retrieved by receiving sunlight reflected from the targets.A filed measurement of NO2 concentration is performed with the ToTaL-DOAS system in Shijiazhuang in the autumn of 2011.The measurement data are compared with concentrations measured by the point monitoring technique at the same site.The results show that the ToTaL-DOAS system is sensitive to the variation of NO2 concentrations along the optical path.     

Electronic transitions of fluorene, dibenzofuran, carbazole, and dibenzothiophene: From the onset of absorption to the ionization threshold

A comparative study of the electronic transitions of fluorene and its hetero-analogues dibenzofuran, carbazole, and dibenzothiophene was performed in a wide energy range. Gas phase, crystal phase, and linear dichroism electronic transmittance spectra were measured with synchrotron radiation. Electronic transitions to excited singlet states were predicted with time-dependent density functional theory, TD-B3LYP/6-31+G(d,p). Based on the experimental and theoretical results, symmetry assignments of electronic transitions in the vacuum and near-UV region are suggested. The correspondence between excited states in these molecules, similarities, and differences between their electronic spectra are discussed.