Generalized gaussian model for uniaxial rotational motion: application to the calculation of spectroscopic responses

An exact model aimed at describing uniaxial rotational motions, based on a rotational adapted Gaussian statistics, is presented. In its simplest form, it depends on only two parameters, an order parameter which can vary from 1 (perfect order) to 0 (isotropic diffusion) and a time-dependent correlation parameter rho which varies from 1 to 0 between initial and infinite times. This model yields closed form expressions for the correlation functions relevant to the main spectroscopic techniques (dielectric absorption, light and neutron scattering, NMR line shape, spin-lattice relaxation, etc.) for all values of the two parameters. According to the functional form postulated for rho(t), in particular forms decaying as power laws at long times, one obtains shapes for the spectroscopic correlation functions and spectra that are similar to those experimentally observed in a large variety of complex systems (liquid crystals, polymers, gels, and amorphous and glassy materials), especially in confined geometries, which often resemble "stretched" exponentials. A simple way to introduce time coherent effects through a modification of rho(t) is proposed. Examples of theoretical correlation functions and spectra are presented. Important remarks concerning the application of this model to the analysis of real data are made. This model is the rotational analogue of the Gaussian translational model developed recently (Volino et al. J. Phys. Chem B 2006, 110, 11217).     

Application of Lie algebraic method to the calculation of rotational spectra for linear triatomic molecules

The Hamiltonian describing rotational spectra of linear triatomic molecules has been derived by using the dynamical Lie algebra of symmetry group U1(4) U2(4). After rovibrational interactions being considered, the eigenvalue expression of the Hamiltonian has the form of term value equation commonly used in spectrum analysis. The molecular rotational constants can be obtained by using the expression and fitting it to the observed lines. As an example, the rotational levels of v2 band for transition (02°0-0110) of molecules N2O and HCN have been fitted and the fitting root-mean-square errors (RMS) are 0.00001 and 0.0014 cm-1, respectively.     

A calculation of the isotropic and anisotropic spectral moments of the dipole oscillator strength distribution of N2

We calculate a range of isotropic and anisotropic spectral moments of the dipole oscillator strength distribution for N₂ in the random phase approximation. The internuclear dependence of, in particular, S∥(k) is nonnegligible and vibrationally averaged moments are reported. The results are compared to other calculations and to experiment when available, and we conclude that the scheme gives reliable results. Based on our results, we predict a 10% anisotropy in the stopping power of oriented N₂ molecules.     

Higher approximations for transition matrices and their application to the calculation of atomic spectra

Theoretical and Experimental Chemistry -     

Time-dependent density functional approach for the calculation of inelastic x-ray scattering spectra of molecules

We apply time-dependent density functional theory to study the valence electron excitations of molecules and generalize the typically used time-propagation scheme and Casida's method to calculate the full wavevector dependent response function. This allows the computational study of dipole-forbidden valence electron transitions and the dispersion of spectral weight as a function of the wavevector. The method provides a novel analysis tool for spectroscopic methods such as inelastic x-ray scattering and electron energy loss spectroscopy. We present results for benzene and CF(3)Cl and make a comparison with experimental results.     

A full multiple scattering model for the analysis of time-resolved X-ray difference absorption spectra

A full multiple theoretical model (MXAN) is applied to fit picosecond difference X-ray absorption spectra at the ruthenium L(3) edge upon photoexcitation of aqueous [RuII(bpy)3]2+. We show that fitting difference spectra allows an increase in sensitivity, such that slight structural changes can be retrieved, which are not detected in fitting full spectra. The Ru-N bond distances of the excited complex in the (3)MLCT state are in good agreement with recently published values. The implementation of the present approach to L-edge spectra and its high sensitivity opens opportunities for its extension to a large class of experiments where difference X-ray absorption spectra are recorded.     

Resonance Rayleigh scattering spectra of Cu2+-adenine-WO4(2-) system and its analytical application

In pH 6.6-7.2 Tris-HCl buffer, Cu(2+) could react with adenine (A) to form a 1:1 coordination cation [CuA](2+), which only resulted in minor change of the absorption spectrum. However, when this cation further combined with WO(4)(2-) to form a 1:1 ternary ion-association complex [CuA]WO(4), the absorption spectrum changed a lot, and the resonance Rayleigh scattering (RRS), second-order scattering (SOS) and frequency doubling scattering (FDS) enhanced significantly. The maximum wavelengths of RRS, SOS and FDS were located at 310, 592 and 395 nm, respectively. The enhanced intensities of the three methods were proportional to the concentration of adenine in certain ranges, and the detection limit of the most sensitive RRS method was 7.4 × 10(-9) mol L(-1) (1.0 ng mL(-1)), indicating that this method could detect trace adenine. In this work, the optimum reaction conditions and the influencing factors have been studied, some potential interferences and the composition of the ion-association complex have been investigated. Meanwhile, the construction of the product and the reaction mechanism have been investigated by atomic force microscopy, transmission electron microscope and quantum chemical calculation. Accordingly, a novel RRS method for determination of adenine has been proposed and applied to detect adenine in real samples with satisfactory results.     

Perturbative solution of the RPA equation. An application to the calculation of rotational strengths

The RPA equation is solved by perturbation in Møller-Plesset (MP) and Epstein-Nesbet (EN) partitions, which are first compared on a specific example. To still accelerate the faster one (EN), a third scheme is proposed, which involves preliminary diagonalization within a limited subset , followed by usual EN perturbation between and the rest of the whole configuration space. Criteria for the choice of are given.     

Linearly and circularly polarized raman spectra of the iron (II) bis[1-(2'-pyridylmethyleneamino)-2-aminoethane] ion evidence for asymmetric raman tensor

Raman spectra of solutions of iron(II)bis[1-(2'-pyridylmethyleneamino)-2-aminoethane] iodide in acetonitrile were recorded using both linearly and circularly polarized light for excitation. The tensor invariants 45$\text{}\text{?}$ga², 7γ_s² and 5γ_as² were determined for three prominent lines with 488.0, 514.5 and 528.7 nm excitation. With two of the lines, significant anti-symmetric anisotropies are found.     

一个新的用于反应散射计算的L^2平动基函数集合

本文通过构造新的L^2平动基函数集合改进了Shima-Baer方法.新集合中不再含有任何人工可调参数,取而代之的是反应体系的分子特性常数.由于在平动基函数中含有在非经典区域内的高度衰减因子,从而大大提高了反应几率对平动基函数展开的收敛速度.对共线交换反应H+H~2→H~2+H的计算结果表果,对平均基函数展开的收敛速度已接近包含畸变势的计算结果.改进后的Shima-Baer方法计算量明显降低.     

A computational method for multi-channel scattering calculations. Applications to rotational excitation and long-lived states of He-N2

A computational scheme is reported which uses a reference potential approximation to provide an efficient numerical solution of the multi-channel Volterra integral equation. Applications to rotational inelastic scattering and quasi-bound states of the He-N₂ system are presented, together with a discussion of the effects of varying the number of closed channels.     

A comparative study of rotational temperatures using diatomic OH,O2 and N2+ molecular spectra emitted from atmospheric plasmas

From the application point of view, gas temperature is one of the most important parameters for atmospheric plasmas. Based on the fact that the gas temperature is closely related with the rotational temperature of an atmospheric plasma, a spectroscopic method of measuring the rotational temperature is described in this work by analyzing OH, O₂ and N₂⁺ molecular spectra emitted from the atmospheric plasma in ambient air. The OH and N₂⁺ molecular spectra are emitted because of the oxygen, hydrogen and nitrogen atoms existing in the ambient air. The O₂ diatomic molecular spectrum is emitted from the oxygen plasma that is frequently produced for atmospheric plasma applications. In order to utilize a spectrometer with modest spectral resolution, a synthetic diatomic molecular spectrum was compared with the experimentally obtained spectrum. The rotational temperatures determined by the above three different molecular spectra are in good agreement within 2.4% error. In the case of a plasma with low gas temperature, the temperature measured by a thermocouple was compared to verify the accuracy of the spectroscopic method, and the results show excellent agreement. From the study, it was found that an appropriate diatomic molecular species can be chosen to be used as a thermometer depending on experimental circumstances.     

The quantum mechanical calculation of rotational spectra. A comparison of methods for C2H2, HCN, HNC, HCO+, N2H+, CO and N2. Predictions for HCNH+, COH+, HBO, HBNH, and HBF+

Rotational frequencies determined with ab initio molecular orbital theory can play an important role in guiding spectroscopic searches for new molecules and in corroborating the assignment of unidentified lines, from the laboratory and from space. In a systematic study of 22 levels of molecular orbital theory, CISD/6-311G** gave rotational frequencies to an accuracy of +/- 0.4 GHz when an empirical correction is applied to the results for C2H2,HCN, HNC, HCO+, N2H+, CO, and N2. Larger errors can be expected when there are large vibrational effects on the rotational constants, as exemplified by COH+. Predicted J = 0--> 1 rotational frequencies using these methods are 73.9 +/- 0.4 GHz for HCNH+, 78.6 +/- 0.4 GHz for HBO, 65.8 +/- 0.4 GHz for HBNH, and 72.1 +/- 0.4 GHz for HBF+.     

Theoretical and experimental studies of CH3X-Y2 rotational line shapes for atmospheric spectra modelling: application to room-temperature CH3Cl-O2

The case of symmetric tops CH(3)X (X = Br, Cl, F, …) perturbed by non-polar diatoms Y(2) (Y = N(2), O(2), …) is analysed from the viewpoint of theoretical collisional broadening of their rotational lines observed in atmospheric spectra. A semi-classical approach involving an exponential representation of the scattering operator and exact trajectories governed by the isotropic potential is presented. For the first time the active molecule is strictly treated as a symmetric top and the atom-atom interactions are included in the intermolecular potential model. It is shown for the CH(3)Cl-O(2) system that these interactions contribute significantly to the line width for all values of the rotational quantum numbers J and K. Additional testing of modifications required in the semi-classical formalism for a correct application of the cumulant expansion is performed and it is shown that the use of the cumulant average on the rotational states of the perturbing molecule leads to entirely negligible effects for the not very strongly interacting CH(3)Cl-O(2) system. In order to check the theoretical predictions and to extend the scarce experimental data available in the literature to higher values of the rotational quantum numbers, new measurements of room-temperature O(2)-broadened CH(3)Cl rotational lines are carried out by a photomixing continuous-wave terahertz spectrometer. The experimental line widths extracted with a Voigt profile model demonstrate an excellent agreement with theoretical results up to very high J-values (J = 31, 37, 40, 45, 50).     

钴-TAN-阴离子表面活性剂体系的共振瑞利散射及其分析应用

研究了Co2 与1-(2-噻唑偶氮)-2-萘酚(TAN)、十二烷基苯磺酸钠(SD-BS)作用的共振瑞利散射光谱,在pH 8.0的BR缓冲溶液中,Co2 的加入导致体系共振光散射的增强,其增强强度与Co2 的质量浓度呈线性关系,据此建立了一种测定Co2 的共振光散射法。该法的线性范围为0~600 ng/mL,相关系数为r=0.9990,检出限为2.25 ng/mL。将该法用于人发、茶叶、维生素B12中Co2 的测定,加标回收率为99.83%~105.4%。     

New signal processing method for the faster observation of natural-abundance 15N NMR spectra and its application to N5+

The new harmonic inversion noise reduction method was applied to (15)N natural-abundance NMR spectroscopy and N(5)SbF(6). This method is superior to conventional Fourier transform methods for processing FIDs and permits the detection of natural abundance (15)N NMR signals with significantly reduced numbers of scans and improved sensitivity. In addition to the confirmation of the previously reported chemical shifts for N(5)(+), the one bond coupling between N(beta) and N(gamma) could be observed for the first time. Its absolute value is compared to known coupling constants of other covalent azides and the free azide ion.     

Model potential calculation of the HHe interaction; application to low energy elastic scattering

Recent model potential calculations of the HHe interaction potential by Valiron et al. are applied to the calculation of the cross section for elastic scattering of H and D by He at very low energies (of the order of several meV). Agreement with the experimental data is excellent. In view of the sensitivity of the cross sections to the interaction potential, it is established that our model potential method is highly accurate in describing long- and intermediate-range interactions.     

An analytical method for the calculation of the relative intensities of bending and stretching modes in inelastic neutron scattering spectra

An approximate analytical method is presented for calculating the relative intensities of the bands due to the stretching (ν) and doubly degenerate b     

A five-dimensional potential energy surface and predicted infrared spectra for the N2O-hydrogen complexes

We present a five-dimensional potential energy surface for the N(2)O-hydrogen complex using supermolecular approach with the full counterpoise correction at the coupled-cluster singles and doubles with noniterative inclusion of connected triple level. The normal mode Q(3) for the nu(3) antisymmetric stretching vibration of the N(2)O molecule was included in the calculations of the potential energies. The radial discrete variable representation/angular finite basis representation method and Lanczos algorithm were employed to calculate the rovibrational energy levels for four species of N(2)O-hydrogen complexes (N(2)O-para-H(2), -ortho-H(2), -ortho-D(2), and -para-D(2)) without separating the inter- and intramolecular vibrations. The calculated band origins are all blueshifted relative to the isolated N(2)O molecule and in good agreement with the experimental values. The calculated rotational spectroscopic constants and molecular structures agree well with the available experimental results. The frequencies and line intensities of the rovibrational transitions in the nu(3) region of N(2)O for the van der Waals ground vibrational state were calculated and compared with the observed spectra. The predicted infrared spectra are consistent with the observed spectra and show that the N(2)O-H(2) complexes are mostly a-type transitions while both a-type and b-type transitions are significant for the N(2)O-D(2) complexes.