The dispersions of the top interface optical phonons and the side interface optical phonons in cylindrical quantum dots are solved by using the dielectric continuum model. Our calculation mainly focuses on the frequen...The dispersions of the top interface optical phonons and the side interface optical phonons in cylindrical quantum dots are solved by using the dielectric continuum model. Our calculation mainly focuses on the frequency dependence of the IO phonon modes on the wave-vector and quantum number in the cylindrical quantum dot system.Results reveal that the frequency of top interface optical phonon sensitively depends on the discrete wave-vector in z direction and the azimuthal quantum number, while that of the side interface optical phonon mode depends on the radial and azimuthal quantum numbers. These features are obviously different from those in quantum well, quantum well wire,and spherical quantum dot systems. The limited frequencies of interface optical modes for the large wave-vector or quantum number approach two certain constant values, and the math and physical reasons for this feature have been explained reasonably.展开更多
The vibrational spectrum of the CaAl2B2O7 was investigated. It was shown that the vibrations of the BO3 groups are present in the region of 1400600 cm-1, and the bands at 519 nm-1 may originate from the AlO6 vibration...The vibrational spectrum of the CaAl2B2O7 was investigated. It was shown that the vibrations of the BO3 groups are present in the region of 1400600 cm-1, and the bands at 519 nm-1 may originate from the AlO6 vibration. The luminescence properties of Eu3+ in CaAl2B2O7 were investigated. It was found that the Eu3+ ion in CaAl2B2O7 occupies two different sites. Investigation on the phonon sideband of Eu3+ indicates that BO3 groups are present in the surroundings of Eu3+ ions.展开更多
The soft terrain spectrum is subdivided into three strands. i.e., the original spectrum,the effective spectrum and the rut spectrum. Accordingly, a device for measurements of all thesespetra is developed Based or its ...The soft terrain spectrum is subdivided into three strands. i.e., the original spectrum,the effective spectrum and the rut spectrum. Accordingly, a device for measurements of all thesespetra is developed Based or its measuring results. a dynamic deformation model of theinteraction between vehicle and soft terrain and ancther modelof smoothing the enveloping pro-file of tyre contact area on soft terrain are proposed for further discussion of forming methanismof soft terrain spectrum which dominates vehicle vibration.展开更多
A 3D finite element model of the Huaiyin third pumping station of the Eastern Route of the South-to-North Water Transfer is described in this paper. Two methods were used in the calculation and vibration analysis of t...A 3D finite element model of the Huaiyin third pumping station of the Eastern Route of the South-to-North Water Transfer is described in this paper. Two methods were used in the calculation and vibration analysis of the pumping station in both the time domain and the frequency domain. The pressure pulsation field of the whole flow passage was structured on the basis of pressure pulsations recorded at some locations of the physical model test. Dynamic time-history analysis of the pump house under pressure pulsations was carried out. At the same time, according to spectrum characteristics of the pressure pulsations at measuring points and results of free vibration characteristics analysis of the pump house, the spectrum analysis method of random vibration was used to calculate dynamic responses of the pump house. Results from both methods are consistent, which indicates that they are both reasonable. The results can be used for reference in anti-vibration safety evaluation of the Huaiyin third pumping station.展开更多
In broadband coherent anti-Stokes Raman scattering （CARS） spectroscopy with supercontinuum （SC）, the simultaneously detectable spectral coverage is limited by the spectral continuity and the simultaneity of variou...In broadband coherent anti-Stokes Raman scattering （CARS） spectroscopy with supercontinuum （SC）, the simultaneously detectable spectral coverage is limited by the spectral continuity and the simultaneity of various spectral components of SC in an enough bandwidth. By numerical simulations, the optimal experimental conditions for improving the SC are obtained. The broadband time-resolved CARS spectrography based on the SC with required temporal and spectral distributions is realised. The global molecular vibrational spectrum with well suppressed nonresonant background noise can be obtained in a single measurement. At the same time, the measurements of dephasing times of various molecular vibrational modes can be conveniently achieved from intensities of a sequence of time-resolved CARS signals. It will be more helpful to provide a complete picture of molecular vibrations, and to exhibit a potential to understand not only both the solvent dynamics and the solute-solvent interactions, but also the mechanisms of chemical reactions in the fields of biology, chemistry and material science.展开更多
Normal vibrations of ethylbenzene in the first excited state have been studied using resonant two-photon ionization spectroscopy. The band origin of ethylbenzene of S1-S0 transition appeared at 37586 cm-1. A vibration...Normal vibrations of ethylbenzene in the first excited state have been studied using resonant two-photon ionization spectroscopy. The band origin of ethylbenzene of S1-S0 transition appeared at 37586 cm-1. A vibrational spectrum of 2000 cm-1 above the band origin in the first excited state has been obtained. Several chain torsions and normal vibrations are obtained in the spectrum. The energies of the first excited state are calculated by the time- dependent density function theory and configuration interaction singles （CIS） methods with various basis sets. The optimized structures and vibrational frequencies of the So and S1 states are calculated using Hartree-Fock and CIS methods with 6-311＋＋G（2d,2p） basis set. The calculated geometric structures in the So and $1 states are gauche conformations that the symmetric plane of ethyl group is perpendicular to the ring plane. All the observed spectral bands have been successfully assigned with the help of our calculations.展开更多
Volterra series is a powerful mathematical tool for nonlinear system analysis,and there is a wide range of nonlinear engineering systems and structures that can be represented by a Volterra series model.In the present...Volterra series is a powerful mathematical tool for nonlinear system analysis,and there is a wide range of nonlinear engineering systems and structures that can be represented by a Volterra series model.In the present study,the random vibration of nonlinear systems is investigated using Volterra series.Analytical expressions were derived for the calculation of the output power spectral density（PSD） and input-output cross-PSD for nonlinear systems subjected to Gaussian excitation.Based on these expressions,it was revealed that both the output PSD and the input-output crossPSD can be expressed as polynomial functions of the nonlinear characteristic parameters or the input intensity.Numerical studies were carried out to verify the theoretical analysis result and to demonstrate the effectiveness of the derived relationship.The results reached in this study are of significance to the analysis and design of the nonlinear engineering systems and structures which can be represented by a Volterra series model.展开更多
Time-and frequency-resolved broadband transient grating(BB-TG) spectroscopy is used to distinguish between ground-and excite-electronic state vibrational coherence at different wavelengths. Qualitative theoretical ana...Time-and frequency-resolved broadband transient grating(BB-TG) spectroscopy is used to distinguish between ground-and excite-electronic state vibrational coherence at different wavelengths. Qualitative theoretical analysis using double-sided Feynman diagrams indicates that a superposition of ground and excited state vibrational coherence are contained in the ground state absorption(GSA) and stimulated emission(SE) overlap band, while only the excited state is contained in the excited state absorption(ESA) band. The TG experiment, in which a white light continuum(WLC) is adopted as a probe, is conducted with rhodamine101(Rh101~+) as the target molecule. Fourier analysis of TG dynamics in a positive delay time range at specific wavelengths enables us to distinguish the low-frequency vibrational modes of Rh101 in ground-and excite-electronic states.展开更多
The harmonic force field and the vibrational spectrum of nitramide were calculated by using the ab initio gradient program TEXAS at the Hartree-Fock level with a 4-21G basis set. The directly computed theoretical harm...The harmonic force field and the vibrational spectrum of nitramide were calculated by using the ab initio gradient program TEXAS at the Hartree-Fock level with a 4-21G basis set. The directly computed theoretical harmonic force field was scaled by using empirical scale factors which are transferred from other molecules and provided an a priori prediction of fundamental frequencies and intensities. The average deviations between predicted vibrational frequencies of nitramide and experimental IR spectrum in an argon matrix are 63 cm-1 for symmetric vibrations and 41 cm-1 for antisymmetric modes. A new set of scale factors was optimized in this paper. These scale factors reduced the average deviations to 2. 3 cm-1 for symmetric modes and 0. 8 cm-1 for antisymmetric ones. The vibrational spectra of three isotopic derivatives of nitramide were predicted by using the force field resulted from the optimized set of scale factors, which are in good agreement with their experimental data in an argon matrix.展开更多
Formaldehyde and hydrogen peroxide are two important realistic molecules in atmospheric chemistry.We implement path integral Liouville dynamics(PILD)to calculate the dipolederivative autocorrelation function for obtai...Formaldehyde and hydrogen peroxide are two important realistic molecules in atmospheric chemistry.We implement path integral Liouville dynamics(PILD)to calculate the dipolederivative autocorrelation function for obtaining the infrared spectrum.In comparison to exact vibrational frequencies,PILD faithfully captures most nuclear quantum effects in vibrational dynamics as temperature changes and as the isotopic substitution occurs.展开更多
The iR and Raman spectra were rrieasured for[Fe_2Cr(μ_3-O)-(glycine)_6 (H_2O)_3] (NO_3)_7. 3H2O in the range of 2000～90 cm￣-1. The assignment of the main skeleton vibrations was made in comparison with related comp...The iR and Raman spectra were rrieasured for[Fe_2Cr(μ_3-O)-(glycine)_6 (H_2O)_3] (NO_3)_7. 3H2O in the range of 2000～90 cm￣-1. The assignment of the main skeleton vibrations was made in comparison with related compounds. A simplified model as well as a simplified general valence force field was used in the normal coordinate analysis of the skeleton and a set of force constants has been obtained. The calculated frequencies agree well with the observed ones, with a mean deviation of 1.8% which confirms the assignn: ient of their vibrational spectra. On the basis of the data obtained some discussions were made.展开更多
The computational modelling supported by experimental results can explain the molecular structure, vibrational assignments, reactive sites and several structural properties. In this context, the spectroscopic (FT-IR, ...The computational modelling supported by experimental results can explain the molecular structure, vibrational assignments, reactive sites and several structural properties. In this context, the spectroscopic (FT-IR, FT-Raman and NMR) analysis, electronic properties (HOMO and LUMO energies) and molecular structure of pyrimethamine (Pyr) were investigated by density functional theory (DFT) method associated with three levels of theory viz., B3LYP, MN15 and wB97XD with 6-311++G(d,p) and def2TZVPP as basis sets, respectively in the Gaussian 16 programs. The <sup>1</sup>H and <sup>13</sup>C NMR chemical shifts were calculated with a gauge-independent atomic orbital (GIAO) approach by also applying the same levels of theory and basis sets. All experimental results were compared with theoretical data. Although the results revealed high degrees of correlation between the theoretical and experimental values for spectroscopic properties using the three methods. Furthermore, the atomic and natural charges, energy band gap and chemical reactivity were determined, while the frontier molecular orbital (FMO) and molecular electrostatic potential (MEP) surfaces were plotted to explain the reactive nature of the title molecule.展开更多
Noticing that the equation with double-Poisson bracket, where On is normal coordinate, Hc is classical Hamiltonian, is the classical correspondence of the invariant eigen-operator equation （2004 Phys. Left. A. 321 75...Noticing that the equation with double-Poisson bracket, where On is normal coordinate, Hc is classical Hamiltonian, is the classical correspondence of the invariant eigen-operator equation （2004 Phys. Left. A. 321 75）, we can find normal coordinates in harmonic crystal by virtue of the invaxiant eigen-operator method.展开更多
The equilibrium structures and the electronic, spectroscopic and thermodynamic properties of small Pun （n = 2- 5） molecules are systematically investigated using the methods of general gradient approximation （GGA）...The equilibrium structures and the electronic, spectroscopic and thermodynamic properties of small Pun （n = 2- 5） molecules are systematically investigated using the methods of general gradient approximation （GGA） of density functional theory （DFT）. The results show that the bond length of the lowest-energy structure of Pu2 is 2.578 A. The ground state structure of Pu3 is a triangle with D3h symmetry, whereas for Pu4, the ground state structure is a square （D4h） and the spin polarization of 16 for molecule Pu5 with square geometry （D_4h） is the most stable structure. For the ground state structures, the vibrational spectra as well as thermodynamic parameters are worked out. In addition, the values for the highest occupied molecular orbital （HOMO） and the lowest unoccupied molecular orbital （LUMO） along with the energy gap of all the Pu_2-5 structures are presented. The relevant structural and chemical stabilities are predicted.展开更多
The purpose of this work was to use a nondestructive method for detecting the brownheart of Korla pear to reduce the chance of infection among pears without brownheart.A mechanical impulse method based on vibration te...The purpose of this work was to use a nondestructive method for detecting the brownheart of Korla pear to reduce the chance of infection among pears without brownheart.A mechanical impulse method based on vibration testing system was used to excite the fruits.The consistent acquisition signal indicated that the test is repeatable at the same positions of fruit equator(cheek).A remarkable frequency signal was excited at 9-12 N force by a rubber tipped hammer.The dominant frequency was identified at the maximum response magnitude to assess the internal defect,and the result was not influenced by the distances between the defect borders and the excitation points.The sharp increase of defect mass could significantly affect the dominant frequency.Relationship between the dominant response frequency(fd)and the defect mass percentage(ω)was characterized by an equation fd=410.649e-0.0833ω+261.947 with a good correlation coefficient(R2=0.925).A defect mass of 2.281%was determined as a discrimination threshold.Once the threshold exceeded 2.281%,the defective pear could be classified with a high accuracy rate of 96.7%.This finding would provide guidance for determining the optimal detecting time to the brownheart of Korla pears,according to the specific storage conditions when the vibration frequency spectrum method is deployed.展开更多
The optimized molecular geometries of the three rotamers of m-dimethoxybenzene in the ground So and electronically excited Sl states were predicted by ab initio and density functional theory （DFF） calculations. Thei...The optimized molecular geometries of the three rotamers of m-dimethoxybenzene in the ground So and electronically excited Sl states were predicted by ab initio and density functional theory （DFF） calculations. Their vibrational spectra in the St state were studied by one color resonant two photon ionization （1C-R2PI） method, and their ionization energies were measured by two color resonant two photon ionization （2C-R2PI） experiment. The optimized molecular geometries showed that the total energy of conformer a was the lowest in the So state. Most of the active vibrations assigned from the 1C-R2PI spectrum were found to be of the in-plane ring modes. The ionization energies （IE） of conformers a, b and c were determined to be 63521, 64487 and 63755 cm^-1, respectively.展开更多
The equilibrium structures, the charge population, and the spectroscopic properties of UO, UO2, UO3, and U2O3 molecules are systematically investigated using the density functional theory （DFT） with the method of ge...The equilibrium structures, the charge population, and the spectroscopic properties of UO, UO2, UO3, and U2O3 molecules are systematically investigated using the density functional theory （DFT） with the method of generalized gradient approximation （GGA）. The bond lengths and the vibrational frequencies of the ground states of UO, UO2, and UO3 molecules are all in agreement with available experimental data. For U2O3 molecules, our calculations indicate that the ground state of the U203 molecule is an XTA1 state with Dah （trigonal bipyramid） symmetry （R1 （U O）=0.2113 nm, R2（U1 U2）=0.2921 nm, ZU1OU2 = 87.5° , dihedral angle O（U,O1,O2,O3）=62.40°）. The harmonic frequency, the IR intensity and the spin density of the U2Oa molecule are all obtained for the first time in theory. For the ground state of U203 molecules, the vibrational frequencies are 178.46 （Ai）, 276.79 （E1＇＇）, 310.77 （EL）, 396.63 （AS＇）, 579.15 （El）, and 614.98 （A1＇） cm-1. The vibrational modes corresponding to the IR maximum peaks are worked out for UO3 and U203 molecules. Besides, the results of Gophinatan-Jng bond order indicate that UO, UO2, and UO3 molecules possess U=O double bonds and that the U203 molecule possesses U O single bonds and a U-U single bond.展开更多
A dual-time method is introduced to calculate the unsteady flow in a certain vibrating flat cascade. An implicit lower-upper symmetric-gauss-seidel scheme（LU-SGS） is applied for time stepping in pseudo time domains,...A dual-time method is introduced to calculate the unsteady flow in a certain vibrating flat cascade. An implicit lower-upper symmetric-gauss-seidel scheme（LU-SGS） is applied for time stepping in pseudo time domains, and the convection items are discretized with the spatial three-order weighted non-oscillatory and non-free-parameter dissipation difference （WNND） scheme. The turbulence model adopts q-co low-Reynolds-number model. The frequency specmuns of lift coefficients and the unsteady pressure-difference coefficients at different spanwise heights as well as the entropy contours at blade tips on different vibrating instants, are obtained. By the analysis of frequency specmuns of lift coefficients at three spanwise heights, it is considered that there exist obvious non-linear perturbations in the flow induced by the vibrating, and the perturbation frequencies are higher than the basic frequency. The entropy contours at blade tips at different times display an intensively unsteady attribute of the flow under large amplitudes.展开更多
文摘The dispersions of the top interface optical phonons and the side interface optical phonons in cylindrical quantum dots are solved by using the dielectric continuum model. Our calculation mainly focuses on the frequency dependence of the IO phonon modes on the wave-vector and quantum number in the cylindrical quantum dot system.Results reveal that the frequency of top interface optical phonon sensitively depends on the discrete wave-vector in z direction and the azimuthal quantum number, while that of the side interface optical phonon mode depends on the radial and azimuthal quantum numbers. These features are obviously different from those in quantum well, quantum well wire,and spherical quantum dot systems. The limited frequencies of interface optical modes for the large wave-vector or quantum number approach two certain constant values, and the math and physical reasons for this feature have been explained reasonably.
文摘The vibrational spectrum of the CaAl2B2O7 was investigated. It was shown that the vibrations of the BO3 groups are present in the region of 1400600 cm-1, and the bands at 519 nm-1 may originate from the AlO6 vibration. The luminescence properties of Eu3+ in CaAl2B2O7 were investigated. It was found that the Eu3+ ion in CaAl2B2O7 occupies two different sites. Investigation on the phonon sideband of Eu3+ indicates that BO3 groups are present in the surroundings of Eu3+ ions.
文摘The soft terrain spectrum is subdivided into three strands. i.e., the original spectrum,the effective spectrum and the rut spectrum. Accordingly, a device for measurements of all thesespetra is developed Based or its measuring results. a dynamic deformation model of theinteraction between vehicle and soft terrain and ancther modelof smoothing the enveloping pro-file of tyre contact area on soft terrain are proposed for further discussion of forming methanismof soft terrain spectrum which dominates vehicle vibration.
基金supported by the National Science and Technology Support Program of China (Program for theEleventh Five-Year Plan, Grant No. 2006BAB04A03)the National Natural Science Foundation of China(Grant No. 10702019)
文摘A 3D finite element model of the Huaiyin third pumping station of the Eastern Route of the South-to-North Water Transfer is described in this paper. Two methods were used in the calculation and vibration analysis of the pumping station in both the time domain and the frequency domain. The pressure pulsation field of the whole flow passage was structured on the basis of pressure pulsations recorded at some locations of the physical model test. Dynamic time-history analysis of the pump house under pressure pulsations was carried out. At the same time, according to spectrum characteristics of the pressure pulsations at measuring points and results of free vibration characteristics analysis of the pump house, the spectrum analysis method of random vibration was used to calculate dynamic responses of the pump house. Results from both methods are consistent, which indicates that they are both reasonable. The results can be used for reference in anti-vibration safety evaluation of the Huaiyin third pumping station.
基金This work was supported by the Innovation Program for Quantum Science and Technology(2021ZD0303305 to Daiqian Xie)by the National Natural Science Foundation of China(No.22073042 and No.22122302 to Xixi Hu,No.22233003 and No.22241302 to Daiqian Xie)。
基金Project supported by the National Natural Science Foundation of China(Grant No.60627003)the Foundation for Creative Team in Institution of Higher Education of Guangdong Province,China(Grant No.06CXTD009)
文摘In broadband coherent anti-Stokes Raman scattering （CARS） spectroscopy with supercontinuum （SC）, the simultaneously detectable spectral coverage is limited by the spectral continuity and the simultaneity of various spectral components of SC in an enough bandwidth. By numerical simulations, the optimal experimental conditions for improving the SC are obtained. The broadband time-resolved CARS spectrography based on the SC with required temporal and spectral distributions is realised. The global molecular vibrational spectrum with well suppressed nonresonant background noise can be obtained in a single measurement. At the same time, the measurements of dephasing times of various molecular vibrational modes can be conveniently achieved from intensities of a sequence of time-resolved CARS signals. It will be more helpful to provide a complete picture of molecular vibrations, and to exhibit a potential to understand not only both the solvent dynamics and the solute-solvent interactions, but also the mechanisms of chemical reactions in the fields of biology, chemistry and material science.
文摘Normal vibrations of ethylbenzene in the first excited state have been studied using resonant two-photon ionization spectroscopy. The band origin of ethylbenzene of S1-S0 transition appeared at 37586 cm-1. A vibrational spectrum of 2000 cm-1 above the band origin in the first excited state has been obtained. Several chain torsions and normal vibrations are obtained in the spectrum. The energies of the first excited state are calculated by the time- dependent density function theory and configuration interaction singles （CIS） methods with various basis sets. The optimized structures and vibrational frequencies of the So and S1 states are calculated using Hartree-Fock and CIS methods with 6-311＋＋G（2d,2p） basis set. The calculated geometric structures in the So and $1 states are gauche conformations that the symmetric plane of ethyl group is perpendicular to the ring plane. All the observed spectral bands have been successfully assigned with the help of our calculations.
基金supported by the National Science Fund for Distinguished Young Scholars (11125209)the National Natural Science Foundation of China (10902068,51121063 and 10702039)+1 种基金the Shanghai Pujiang Program (10PJ1406000)the Opening Project of State Key Laboratory of Mechanical System and Vibration (MSV201103)
文摘Volterra series is a powerful mathematical tool for nonlinear system analysis,and there is a wide range of nonlinear engineering systems and structures that can be represented by a Volterra series model.In the present study,the random vibration of nonlinear systems is investigated using Volterra series.Analytical expressions were derived for the calculation of the output power spectral density（PSD） and input-output cross-PSD for nonlinear systems subjected to Gaussian excitation.Based on these expressions,it was revealed that both the output PSD and the input-output crossPSD can be expressed as polynomial functions of the nonlinear characteristic parameters or the input intensity.Numerical studies were carried out to verify the theoretical analysis result and to demonstrate the effectiveness of the derived relationship.The results reached in this study are of significance to the analysis and design of the nonlinear engineering systems and structures which can be represented by a Volterra series model.
基金Project supported by the Science Challenge Project,China(Grant No.TZ2016001)the National Natural Science Foundation of China(Grant No.21673211)
文摘Time-and frequency-resolved broadband transient grating(BB-TG) spectroscopy is used to distinguish between ground-and excite-electronic state vibrational coherence at different wavelengths. Qualitative theoretical analysis using double-sided Feynman diagrams indicates that a superposition of ground and excited state vibrational coherence are contained in the ground state absorption(GSA) and stimulated emission(SE) overlap band, while only the excited state is contained in the excited state absorption(ESA) band. The TG experiment, in which a white light continuum(WLC) is adopted as a probe, is conducted with rhodamine101(Rh101~+) as the target molecule. Fourier analysis of TG dynamics in a positive delay time range at specific wavelengths enables us to distinguish the low-frequency vibrational modes of Rh101 in ground-and excite-electronic states.
基金Supported by the National Natural Science Foundation of China
文摘The harmonic force field and the vibrational spectrum of nitramide were calculated by using the ab initio gradient program TEXAS at the Hartree-Fock level with a 4-21G basis set. The directly computed theoretical harmonic force field was scaled by using empirical scale factors which are transferred from other molecules and provided an a priori prediction of fundamental frequencies and intensities. The average deviations between predicted vibrational frequencies of nitramide and experimental IR spectrum in an argon matrix are 63 cm-1 for symmetric vibrations and 41 cm-1 for antisymmetric modes. A new set of scale factors was optimized in this paper. These scale factors reduced the average deviations to 2. 3 cm-1 for symmetric modes and 0. 8 cm-1 for antisymmetric ones. The vibrational spectra of three isotopic derivatives of nitramide were predicted by using the force field resulted from the optimized set of scale factors, which are in good agreement with their experimental data in an argon matrix.
文摘Formaldehyde and hydrogen peroxide are two important realistic molecules in atmospheric chemistry.We implement path integral Liouville dynamics(PILD)to calculate the dipolederivative autocorrelation function for obtaining the infrared spectrum.In comparison to exact vibrational frequencies,PILD faithfully captures most nuclear quantum effects in vibrational dynamics as temperature changes and as the isotopic substitution occurs.
文摘The iR and Raman spectra were rrieasured for[Fe_2Cr(μ_3-O)-(glycine)_6 (H_2O)_3] (NO_3)_7. 3H2O in the range of 2000～90 cm￣-1. The assignment of the main skeleton vibrations was made in comparison with related compounds. A simplified model as well as a simplified general valence force field was used in the normal coordinate analysis of the skeleton and a set of force constants has been obtained. The calculated frequencies agree well with the observed ones, with a mean deviation of 1.8% which confirms the assignn: ient of their vibrational spectra. On the basis of the data obtained some discussions were made.
文摘The computational modelling supported by experimental results can explain the molecular structure, vibrational assignments, reactive sites and several structural properties. In this context, the spectroscopic (FT-IR, FT-Raman and NMR) analysis, electronic properties (HOMO and LUMO energies) and molecular structure of pyrimethamine (Pyr) were investigated by density functional theory (DFT) method associated with three levels of theory viz., B3LYP, MN15 and wB97XD with 6-311++G(d,p) and def2TZVPP as basis sets, respectively in the Gaussian 16 programs. The <sup>1</sup>H and <sup>13</sup>C NMR chemical shifts were calculated with a gauge-independent atomic orbital (GIAO) approach by also applying the same levels of theory and basis sets. All experimental results were compared with theoretical data. Although the results revealed high degrees of correlation between the theoretical and experimental values for spectroscopic properties using the three methods. Furthermore, the atomic and natural charges, energy band gap and chemical reactivity were determined, while the frontier molecular orbital (FMO) and molecular electrostatic potential (MEP) surfaces were plotted to explain the reactive nature of the title molecule.
基金supported by the National Natural Science Foundation of China (Grant No. 10574060)the Natural Science Foundation of Shandong Province of China (Grant No. Y2008A23)the Shandong Province Higher Educational Science and Technology Program (Grant No. J09LA07)
文摘Noticing that the equation with double-Poisson bracket, where On is normal coordinate, Hc is classical Hamiltonian, is the classical correspondence of the invariant eigen-operator equation （2004 Phys. Left. A. 321 75）, we can find normal coordinates in harmonic crystal by virtue of the invaxiant eigen-operator method.
文摘The equilibrium structures and the electronic, spectroscopic and thermodynamic properties of small Pun （n = 2- 5） molecules are systematically investigated using the methods of general gradient approximation （GGA） of density functional theory （DFT）. The results show that the bond length of the lowest-energy structure of Pu2 is 2.578 A. The ground state structure of Pu3 is a triangle with D3h symmetry, whereas for Pu4, the ground state structure is a square （D4h） and the spin polarization of 16 for molecule Pu5 with square geometry （D_4h） is the most stable structure. For the ground state structures, the vibrational spectra as well as thermodynamic parameters are worked out. In addition, the values for the highest occupied molecular orbital （HOMO） and the lowest unoccupied molecular orbital （LUMO） along with the energy gap of all the Pu_2-5 structures are presented. The relevant structural and chemical stabilities are predicted.
基金National Natural Science Foundation of China(No.31560476)Specialized Research Fund for the Doctoral Programs of Xinjiang(No.2013BB011).
文摘The purpose of this work was to use a nondestructive method for detecting the brownheart of Korla pear to reduce the chance of infection among pears without brownheart.A mechanical impulse method based on vibration testing system was used to excite the fruits.The consistent acquisition signal indicated that the test is repeatable at the same positions of fruit equator(cheek).A remarkable frequency signal was excited at 9-12 N force by a rubber tipped hammer.The dominant frequency was identified at the maximum response magnitude to assess the internal defect,and the result was not influenced by the distances between the defect borders and the excitation points.The sharp increase of defect mass could significantly affect the dominant frequency.Relationship between the dominant response frequency(fd)and the defect mass percentage(ω)was characterized by an equation fd=410.649e-0.0833ω+261.947 with a good correlation coefficient(R2=0.925).A defect mass of 2.281%was determined as a discrimination threshold.Once the threshold exceeded 2.281%,the defective pear could be classified with a high accuracy rate of 96.7%.This finding would provide guidance for determining the optimal detecting time to the brownheart of Korla pears,according to the specific storage conditions when the vibration frequency spectrum method is deployed.
基金Project supported by the Science Foundation of CSU （No. 76112156） and the Postdoctoral Science Foundation of CSU （No. 748160000）.Acknowledgments We gratefully thank Prof. TZENG, Wen-Bih （IAMS, Academia Sinica, Taipei） for providing the T0F-MS and helpful discussions .
文摘The optimized molecular geometries of the three rotamers of m-dimethoxybenzene in the ground So and electronically excited Sl states were predicted by ab initio and density functional theory （DFF） calculations. Their vibrational spectra in the St state were studied by one color resonant two photon ionization （1C-R2PI） method, and their ionization energies were measured by two color resonant two photon ionization （2C-R2PI） experiment. The optimized molecular geometries showed that the total energy of conformer a was the lowest in the So state. Most of the active vibrations assigned from the 1C-R2PI spectrum were found to be of the in-plane ring modes. The ionization energies （IE） of conformers a, b and c were determined to be 63521, 64487 and 63755 cm^-1, respectively.
文摘The equilibrium structures, the charge population, and the spectroscopic properties of UO, UO2, UO3, and U2O3 molecules are systematically investigated using the density functional theory （DFT） with the method of generalized gradient approximation （GGA）. The bond lengths and the vibrational frequencies of the ground states of UO, UO2, and UO3 molecules are all in agreement with available experimental data. For U2O3 molecules, our calculations indicate that the ground state of the U203 molecule is an XTA1 state with Dah （trigonal bipyramid） symmetry （R1 （U O）=0.2113 nm, R2（U1 U2）=0.2921 nm, ZU1OU2 = 87.5° , dihedral angle O（U,O1,O2,O3）=62.40°）. The harmonic frequency, the IR intensity and the spin density of the U2Oa molecule are all obtained for the first time in theory. For the ground state of U203 molecules, the vibrational frequencies are 178.46 （Ai）, 276.79 （E1＇＇）, 310.77 （EL）, 396.63 （AS＇）, 579.15 （El）, and 614.98 （A1＇） cm-1. The vibrational modes corresponding to the IR maximum peaks are worked out for UO3 and U203 molecules. Besides, the results of Gophinatan-Jng bond order indicate that UO, UO2, and UO3 molecules possess U=O double bonds and that the U203 molecule possesses U O single bonds and a U-U single bond.
基金This Project is supported by National Natural Science Foundation of China (No.50776056)National Hi-tech Research and Development Program of China (863 Program,No.2006AA05Z250).
文摘A dual-time method is introduced to calculate the unsteady flow in a certain vibrating flat cascade. An implicit lower-upper symmetric-gauss-seidel scheme（LU-SGS） is applied for time stepping in pseudo time domains, and the convection items are discretized with the spatial three-order weighted non-oscillatory and non-free-parameter dissipation difference （WNND） scheme. The turbulence model adopts q-co low-Reynolds-number model. The frequency specmuns of lift coefficients and the unsteady pressure-difference coefficients at different spanwise heights as well as the entropy contours at blade tips on different vibrating instants, are obtained. By the analysis of frequency specmuns of lift coefficients at three spanwise heights, it is considered that there exist obvious non-linear perturbations in the flow induced by the vibrating, and the perturbation frequencies are higher than the basic frequency. The entropy contours at blade tips at different times display an intensively unsteady attribute of the flow under large amplitudes.
