Dissociation Energies of CN,PbF, SiF,SnF, SnS and NBr MOLECULES

The ground state dissociation energies of CN, PbF, SiF, SnF, SnS and NBr molecules have been estimated using the empirical electronegativity potential function proposed by Szöke and Baitz. The dissociation energies for these molecules have been found to be 7.9, 3.2, 4.2, 3.2, 3.0 and 2,7 eV respectively and compared with the earlier values.     

Resonance capture of electrons by electroactive organic molecules

Bound states of electrons with electroactive aromatic molecules, promising for use in molecular electronics, are studied employing electron attachment spectroscopy Anions are produced in the gas phase through the capture of electrons with energies of up to 15 eV by molecules via the resonance mechanism. The possible pathways of fragmentation of molecular anions and the times of electron retention by the test molecules at various incident electron energies are measured. The resonance states identified are interpreted with the help of quantum-chemical calculations. The possibility of applying the results obtained to molecular electronics is discussed.     

Geometrical structures,vibrational frequencies,force constants and dissociation energies of isotopic water molecules （H2O,HDO, D2O,HTO, DTO,and T2O） under dipole electric field

The dissociation limits of isotopic water molecules are derived for the ground state. The equilibrium geometries, the vibrational frequencies, the force constants and the dissociation energies for the ground states of all isotopic water molecules under the dipole electric fields from -0.05 a.u. to 0.05 a.u. are calculated using B3P86/6-311++G(3df,3pf). The results show that when the dipole electric fields change from -0.05 a.u. to 0.05 a.u., the bond length of H-O increases whereas the bond angle of H-O-H decreases because of the charge transfer induced by the applied dipole electric field. The vibrational frequencies and the force constants of isotopic water molecules change under the influence of the strong external torque. The dissociation energies increase when the dipole electric fields change from -0.05 a.u. to 0.05 a.u. and the increased dissociation energies are in the order of H2O, HDO, HTO, D2O, DTO, and T2O under the same external electric fields.     

双原子分子振动能谱与离解能的精确研究

代数方法(AM)的建立解决了实验方法和精确量子力学理论方法难以获得双原子分子的包含最高振动能级在内的所有高阶振动能级的精确数值这一问题.基于LeRoy与Bernstein的工作,孙卫国等又建立了精确计算双原子分子离解能的新解析表达式.应用新公式和代数方法(AM),研究了一些双原子分子部分电子态的振动能谱和分子离解能,获得了与实验值符合非常好的理论结果.该方法在理论上提供了获得双原子分子完全振动能谱和精确分子离解能的物理新方法.     

脉冲电晕放电电子能量及OH,O或O3对NO氧化的光谱学研究

采用发射光谱法测量了线板式脉冲电晕放电中激发态氮气分子N2*和离子N2+的光谱强度,并与数值计算获得的结果进行对比,确定放电电场的空间分布及平均电子能量。水平与竖直方向离开线电极0～2cm,随着距离的增加,平均电子能量和电场均呈先减后增的变化趋势;放电电场变化范围11.05～19.6MV.m-1,对应的平均电子能量的变化范围10.10～13.92eV。这一能量水平的电子足以与O2,H2O分子碰撞产生O,OH自由基,并进一步反应生成O3。在NO氧化过程中,NO可与OH自由基共存,但不能与O3共存;且O3或O氧化NO的效率高于OH自由基,推断O3或O在NO的氧化过程中起关键作用。     

Losses in the Energy of Low-Energy Electrons in Fluorene, Fluorenone, and Diiodofluorenone Vapors

Electron energy loss spectra (EELS) of fluorene, fluorenone, and diiodofluorenone vapors excited by monokinetic electrons of energies 15–50 eV have been obtained. The singlet and triplet absorption bands of these molecules have been calculated. Comparison of these bands with the experimental EELSs and optical absorption spectra has shown that the forbiddenness of singlet-triplet transitions is not completely removed in the process of interaction of molecules with electrons. The presence of heavy iodine atoms in the diiodofluorenone molecule enhances singlet-triplet transitions. Bands of overtones of stretching vibrations of the CH groups of the benzene rings have been detected near the peak of elastic scattering of electrons of the molecules studied.     

On the contribution of triply-excited and quadruply-excited configurations to electron correlation energies in closed-shell systems

The contribution made by triply-excited and quadruply-excited configurations to electron correlation energies in closed-shell systems is examined in detail. Many-body perturbation theory is used to calculate the contribution of these configurations to the correlation energies in 25 atoms and molecules. Calculations are performed for the nitrogen, carbon monoxide and carbon monosulphide molecules for a range of nuclear geometries.     

静电六极装置电场分布的数值计算方法及在N2O分子转动态选择、取向中的应用

阐述求解极性分子转动态选择及取向静电六极装置中势能分布、电场分布的数值计算方法.为了获得电场分布公式,需通过数值迭代求解势能满足的Laplace方程,获取数值分布点,通过数值分布点,由待定系数的多级展开势能解析表达式进行最小二乘拟合获得势能分布公式,由势能对空间向量的微分获得电场分布.分子在六极电场中的运行轨迹采用经典Newton方程描述,并通过四阶龙格-库塔方法(Four Order Runge-Kutta Method)实现数值求解,其中能量处理采用量子力学方法.应用此方法给出静电六极装置的电场分布公式,运用获得的电场分布公式计算和讨论电场对极性分子N₂O的静电六极转动态选择、取向所带来的影响.     

Path integral Monte Carlo study of(H_2)_n@C_(70)(n = 1, 2, 3)

The path integral Monte Carlo(PIMC) method is employed to study the thermal properties of C70 with one, two,and three H2 molecules confined in the cage, respectively. The interaction energies and vibrationally averaged spatial distributions under different temperatures are calculated to evaluate the stabilities of(H2)n@C70(n = 1, 2, 3). The results show that(H2)2@C70is more stable than H2@C70. The interaction energy slowly changes in a large temperature range,so temperature has little effect on the stability of the system. For H2@C70and(H2)2@C70, the interaction energies keep negative; however, when three H2 molecules are in the cage, the interaction energy rapidly increases to a positive value.This implies that at most two H2 molecules can be trapped by C70. With an increase of temperature, the peak of the spatial distribution gradually shifts away from the center of the cage, but the maximum distance from the center of H2 molecule to the cage center is much smaller than the average radius of C70.     

The correcting method for the estimation of correlation energies of MF2 (M = Be,Mg, Ca) set molecules

The intrapair and interpair correlation energies of MF₂ (M = Be, Mg, Ca) set molecules are calculated and analysed, and the transferability of inner core correlation effects of M^δ+ are investigated. A detailed analysis of the comparison of correlation energies of neutral atoms with their corresponding ions of M^δ+ and F^δ/2 is given in terms of the correlation contribution of this component. The study reveals that the total correlation energy of MF₂ molecules can be obtained by summing the correlation contributions of M^δ+ and two Fδ-/2 components. This simple estimation method does shed light on the importance of searching useful means for the calculation of electron correlation energy for large biological systems.     

On the use of the finite difference method in a calculation of vibration-rotation energies

The use of the finite difference method to obtain a Taylor series expansion of a potential energy function for a subsequent calculation of the rovibration energies of molecules is considered. A method is proposed that allows the stability of a finite-difference scheme to be increased against the computational inaccuracy upon numerical expansion of a multidimensional potential energy function into a high-order Taylor series. The method is based on the successive elimination of calculated expansion coefficients of a higher order in calculating the lower-order coefficients by the finite difference method. The approach is illustrated for the example of the CO and H₂S molecules.     

Direct observation of distorted wave effects in ethylene using the (e,2e) reaction

We report here the direct measurements of electron momentum distributions for ethylene using the (e,2e) reaction at different impact energies from 400 to 2400 eV. The "turn up" effects in the (e,2e) cross sections of the 1b(3g) orbital compared with the plane-wave impulse approximation calculations were observed at low and high momentum regions, and such discrepancies become smaller with the increase of the impact electron energies. It is suggested that the observed discrepancies are due to the distorted-wave effects in molecules, while appropriate theoretical calculations using distorted waves in molecules could not be achieved until now.     

The prediction of core-level binding-energy shifts from CNDO molecular orbitals

A theory is described for calculating core-level binding-energy shifts with potential models that employ “intermediate-level” molecular-orbital wave functions. The relaxation-energy term in atomic core-level binding energies is considered first. The ground-state potential model (GPM) and relaxation-potential model (RPM) are developed for calculating core-level binding energy shifts in molecules from CNDO wavefunctions. It is shown that neglect of certain two- and three-center integrals in these models limits their accuracy when unlike molecules are compared. The models are modified by calculating r^?1 integrals, to be sensitive to bond directions of p orbitals. The pp′ modification, in which a subset of the neglected integrals is retained to recover invariance to coordinate transformations, is thereby necessitated. The GPM approach yields shifts in very good agreement with experiment when comparisons are restricted to similar molecules. The RPM version gives better agreement especially over wider classes of molecules. It also provides relaxation energies V_R that can be combined with ab initio orbital energies to give binding energies. Several applications of these potential models are discussed.     

Electron pairs,localized orbitals and electron correlation

Presuming zeroth-order electronic wavefunctions generated from localized SCF or FORS molecular orbitals, the correlation energy is expressed as a bilinear form in terms of the pair populations of these orbitals and the projections of a correlation operator onto these orbitals. The latter are determined by fitting the correlation energies of large sets of organic molecules, which are reproduced with a mean absolute deviation of 1–3 kcal mol^?1. The resulting formula provides a ‘back-of-the-envelope’ method for estimating correlation energies and furnishes an analysis of these energies in terms of physical concepts and chemical structure. It Predicts the correlation energy of diamond (per carbon atom) to within 6 kcal mol^?1.     

Synchrotron radiation VUV double photoionization of some small molecules

The VUV double photoionizations of small molecules (NO,CO,CO2 ,CS2 ,OSC and NH3 ) were investigated with photoionization mass spectroscopy using synchrotron radiation. The double ionization energies of molecules were determined with photoionization efficiency spectroscopy. The total energies of these molecules and their parent dications (NO2+ ,CO2+ ,CO2+2 ,CS2+2 ,OSC2+ and NH2+3 ) were calculated using the Gaussian 03 program and Gaussian 2 calculations. Then,the adiabatic double ionization energies of the molecules were predicated by using high accuracy energy mode. The experimental double ionization energies of these small molecules were all in reasonable agreement with their respective calculated adiabatic double ionization energies. The mechanisms of double photoionization of these molecules were discussed based on a comparison of our experimental results with those predicted theoretically. The equilibrium geometries and harmonic vibrational frequencies of molecules and their parent dications were calculated by using the MP2 (full) method. The differences in configurations between these molecules and their parent dications were also discussed on the basis of theoretical calculations.     

苯并咪唑苝与金属Ag的界面电子结构研究

利用同步辐射光电子能谱实验技术考察了苯并咪唑苝(BZP)和Ag的界面形成过程与电子结构.单层覆盖度以下时，BZP分子与Ag有弱相互作用，在有机分子禁带中出现明显界面反应态，结合能位于0.9eV.单层铺满后，BZP分子呈现三维岛式生长，且与Ag的相互作用逐渐减弱，同时最高占据分子轨道由于终态效应逐渐向高结合能方向位移至体相结合能位置(2.3eV). Ag衬底上BZP分子的生长导致样品表面功函数减小，表明形成了表面偶极势(Δ=0.3eV)，且电子从有机分子向金属Ag偏移.最后，考察了BZP/Ag 关键词： 有机-金属界面 电子结构 光电子能谱 同步辐射     

Accurate studies on the full vibrational energy spectra and molecular dissociation energies for some electronic states of halogen molecule

This paper obtains accurate vibrational spectroscopic constants and full vibrational energy spectrum by the algebraic method (AM) for some electronic states of halogen diatomic molecules.Motivated by the recent success of obtaining the dissociation energies of Li 2 molecule by using a new analytical formula,it further extends the formula to study the dissociation energies of halogen diatomic molecules.The results show that the AM spectrum and the theoretical dissociation energies agree well with RKR data and experimental data respectively.     

Adsorption kinetics and dynamics of small organic molecules on a silica wafer: Butane, pentane, nonane, thiophene, and methanol adsorption on SiO2/Si(1 1 1)

The adsorption kinetics (by thermal desorption spectroscopy) and adsorption dynamics (by molecular beam scattering) have been determined for a number of alkanes, methanol, thiophene, and water on a silica wafer—SiO₂/Si(1 1 1). No indications for bond activation were present, i.e., all probe molecules adsorb molecularly obeying 1st order kinetics. The coverage-dependent heat of adsorption has been determined accordingly. The adsorption dynamics are precursor-mediated with Kisliuk-like shapes of the adsorption probabilities at low impact energies and adsorbate-assisted adsorption at large impact energies.     

A Theoretical Study of a Single-Walled ZnO Nanotube as a Sensor for H_2 O Molecules

We have studied the property of single-walled ZnO nanotubes with adsorbed water molecules, and theoretically designed a new sensor for detecting water molecules using single-walled ZnO nanotubes using a combination of density functional theory and the non-equilibrium Green's function method. Details of the geometric structures and adsorption energies of the H 2 O molecules on the ZnO nanotube surface have been investigated. Our computational results demonstrate that the formation of hydrogen bonding between the H 2 O molecules and the ZnO nanotube, and adsorption energies of the H 2 O molecules on the ZnO nanotube are larger than the adsorption energies of other gas molecules present in the atmospheric environment. Moreover, the current-voltage curves of the ZnO nanotube with and without H 2 O molecules adsorbed on its surface are calculated, the results of which showed that the H 2 O molecules form stable adsorption configurations that could lead to the decrease in current. These results suggest that the single-walled ZnO nanotubes are able to detect and monitor the presence of H 2 O molecules by applying bias voltages.     

Generating intense beams of low-energy molecules

A method for obtaining intense pulsed beams of molecules possessing low kinetic energies is proposed. The method is based on the formation of a cold pressure shock (shock wave) in an intense pulsed molecular beam interacting with a solid surface, which serves as a source of the secondary beam of low-energy molecules. The proposed method was successfully used to obtain intense beams of H₂, He, CH₄, and Kr molecules with kinetic energies not exceeding 10 meV, and H₂/Kr and He/Kr beams with kinetic energies of H₂ and He molecules below 1 meV.