CH_3F-Ar体系的高精度势能面及预测的振转光谱

本文在从头算CCSD(T)/AVQZ水平上计算了CH_3F-Ar体系包含CH_3F分子Q_3振动的四维势能面.以摩斯长程势(MLR)为模型,分析的三维高精度分子间势能面通过非线性拟合振动平均的基态(v_3=0)和激发态(v_3=1)的能量而得到.其中对2038个格点拟合的方差仅为0.08 cm-1.我们发现,该体系相互作用能的主要贡献来源于短程的交换排斥能和长程的色散能,势能面有3个极小值点,在θ方向表现出强烈的各向异性,而在φ方向各向异性比较弱.与CH_3F-He体系相比,分子间相互作用较强,分子间相互作用对单个分子的束缚较明显,CH_3F和Ar表现得更像紧束缚的超分子.随后,采用径向离散变量表象(DVR)和角度有限基组表象(FBR)相结合的杂化基函数方法进行展开,用Lanzcos迭代的方法计算了该体系的振转能级,并首次报道了该体系的微波、红外光谱.值得指出的是,由于相互作用比较强,形成的势阱较深,该体系在两个不同的势阱中分别形成了分子间振动基态和激发态,这与CH_3F-He体系中全空间离域的能级态形成鲜明的对比.     

人类Y染色体回文序列中的重复序列与碱基关联

利用信息论和统计学的方法并结合生物学的特征研究人类Y染色体回文序列的互信息、“n字”熵、条件熵,定量分析了回文序列的长程关联和短程关联,发现其中既存在长程关联也存在短程关联,并且它们主要是由序列中的重复序列引起的．研究表明重复序列含量越高碱基之间的关联越强．     

对一个大单轴磁各向异性镍(Ⅱ)配合物中的磁跃迁的直接观察（英文）

最近Ruamps和同事发现三角双锥构型的Ni(Ⅱ)配合物[Ni(Me6tren)Cl]ClO4(1,Me6tren=tris(2-(dimethylamino)ethyl)amine)具有大的单轴磁各向异性(J. Am. Chem. Soc., 2013,135:3017-3026)。他们利用HF-EPR研究获得横向零场分裂(ZFS)参数E=1.56(5)cm-1但未能确定轴向零场分裂参数D。在本工作中,我们利用0～17.5 T和5 K的变磁场远红外光谱(FIRMS)来检测自旋基态S=1中的MS=±1和MS=0态之间的磁跃迁。在FIRMS中直接观察到Zeeman分裂态之间的跃迁,得出轴向ZFS参数D=-110.7(3) cm-1。我们对1的晶体结构进行了Hirshfeld表面分析,揭示了1分子中的阳离子与阴离子之间以及分子之间的相互作用。     

D＋CH4反应的SVRT含时波包理论研究

基于Jordan和Gilbert势能面,用SVRT(semirigid vibrating rotor target)模型,对D＋CH4反应进行了含时波包动力学研究,计算得到了不同初始振动转动态的总反应几率、积分散射截面和热速率常数.计算结果与H＋CH4反应进行了比较和讨论.反应几率随平动能的变化曲线呈现出显著的量子共振特性.通过对j=0时,v=0、1、2的反应几率的计算,看出H－CH3的振动激发极大地提高了反应几率,而反应阈能明显降低,说明反应分子的振动能对分子的碰撞反应有重要贡献.对v=0时,j=0、1、2、3的反应几率的计算,得出转动量子数j的增大也会使反应几率有较大的提高,但反应阈能基本不变.     

D CH_4反应的SVRT含时波包理论研究

基于Jordan和Gilbert势能面,用SVRT(semirigidvibratingrotortarget)模型,对D CH4反应进行了含时波包动力学研究,计算得到了不同初始振动转动态的总反应几率、积分散射截面和热速率常数.计算结果与H CH4反应进行了比较和讨论.反应几率随平动能的变化曲线呈现出显著的量子共振特性.通过对j=0时,v=0、1、2的反应几率的计算,看出H-CH3的振动激发极大地提高了反应几率,而反应阈能明显降低,说明反应分子的振动能对分子的碰撞反应有重要贡献.对v=0时,j=0、1、2、3的反应几率的计算,得出转动量子数j的增大也会使反应几率有较大的提高,但反应阈能基本不变.     

NH2(A2A1,090,423)的电子猝灭和转动态-态传能

在束 气和束 束实验条件下,详细研究了NH2(A1,090,423)自由基分别与Ar,N2,O2和NH3碰撞引起的电子态猝灭和转动态 态传能,获得了总的猝灭截面σQ (分别为≤0.17、0.26、0.30和0.48 nm2),以及相对转动态 态传能截面.利用碰撞络合物模型计算的电子猝灭截面与实验测得的截面具有基本相同的趋势,表明长程吸引势在猝灭过程中起着重要的作用.同时还发现,转动态 态传能中相对截面随着碰撞对的折合质量的减小而下降.由于NH3具有较大的偶极矩以及O2的开壳层电子结构使得猝灭截面增大,而转动态 态传能截面减小.     

Na_5P_3O_(10)-Ca(OH)_2-CO_2-H_2O体系纳米CaCO_3的成核与生长

通过化学分析、SEM显微分析技术结合RosinRamiler概率统计理论从介观层次研究Na5P3O10CaOH2CO2H2O体系纳米CaCO3的合成反应及其成核和生长过程。结果表明Na5P3O10对CaOH2的碳化反应具有抑制作用。随着Na5P3O10的增加体系中CaCO3的成核速率B0逐渐增大。在Na5P3O10=0ppm时CaCO3结晶的生长由长程扩散和凝聚生长控制Na5P3O10=380.4760.9ppm时前期受短程扩散和界面反应控制、后期受长程扩散控制。Na5P3O10的存在抑制了纳米CaCO3的晶体生长。     

EuB6的光电导率和能量损失函数谱的理论指认

基于更高精度的能带结构计算结果, 计算EuB6的光电导率和能量损失函数谱, 结果与实验一致. 通过具体计算找出在0-40 eV能量区间内所有可能发生的能带间电子跃迁, 在第一布里渊区中发生跃迁的区域和跃迁概率, 得到了各电子跃迁的始态和末态的单电子波函数. 利用计算结果详细分析了光电导率和能量损失函数各谱峰与能带间电子跃迁的联系. 在此基础上对实验测得的谱峰作出指认, 证实了Kimura等人根据实验结果所作经验指认的合理部分, 指出其中一些不准确的指认, 并补充了他们没有考虑到的一些对谱峰有重要贡献的电子跃迁.     

NH_2(~2A_1,090,4_(23))的电子猝灭和转动态-态传能

在束-气和束-束实验条件下,详细研究了NH_2(~2A_1,090,4_(23))自由基分别与 Ar,N2,O2和 NH3碰撞引起的电子态猝灭和转动态-态传能,获得了总的猝灭截面σQ (分别为≤ 0.17、 0.26、 0.30和 0.48 nm~2),以及相对转动态-态传能截面 .利用碰撞络合物模型计算的电子猝灭截面与实验测得的截面具有基本相同的趋势,表明长程吸引势在猝灭过程中起着重要的作用 .同时还发现,转动态-态传能中相对截面随着碰撞对的折合质量的减小而下降 .由于 NH_3具有较大的偶极矩以及 O_2的开壳层电子结构使得猝灭截面增大,而转动态-态传能截面减小 .     

NH2(A~2A1, 090,423)的电子猝灭和转动态-态传能

在束-气和束-束实验条件下,详细研究了NH2(A2A1,090,423)自由基分别与Ar,N2,O2和NH3碰撞引起的电子态猝灭和转动态-态传能,获得了总的猝灭截面σQ(分别为≤0.17、0.26、0.30和0.48 nm2),以及相对转动态-态传能截面.利用碰撞络合物模型计算的电子猝灭截面与实验测得的截面具有基本相同的趋势,表明长程吸引势在猝灭过程中起着重要的作用.同时还发现,转动态-态传能中相对截面随着碰撞对的折合质量的减小而下降.由于NH3具有较大的偶极矩以及O2的开壳层电子结构使得猝灭截面增大,而转动态-态传能截面减小.     

Classical dependence of polarization on potential energy surface in rotationally inelastic collisions

Quasiclassicol trajectory calculations have been performed for model potential energy surfaces to investigate polarization in (j,m_j) → (j',m_j) integral cross sections For j = 0, it was found that the occurrence of polarization requires an attractive well, and that it be in the collinear configuration Results for j≠ 0 are also presented.     

A study of reorientation effects in CsF—Ar using approximate quantum methods

The EB (exponential Born) and IOS (infinite order sudden) methods are used to calculate a variety of j → j′ and jm → j′m′ integral cross sections and j → j′ differential cross sections for CsF—Ar at E_cm = 87.7 meV. Inelastic rotational cross sections are found to depend primarily on the odd long range parts of the interaction potential. The jm → j′m′ integral cross sections for the quantization axis parallel to the initial relative velocity vector are found to approximately obey the selection rule “Δj + Δm = even” and cross sections for which the orientation of the rotor is left unchanged (i.e. 11 → 11, 11 → 22, and 11 → 33 transitions) are strongly favored over those which are changed for low lying rotational states. Good agreement between the IOS and EB methods is found for most of the scattering quantities calculated.     

Accurate time dependent wave packet calculations for the N + OH reaction

We present accurate quantum calculations of state-to-state cross sections for the N + OH → NO + H reaction performed on the ground (3)A' global adiabatic potential energy surface of Guadagnini et al. [J. Chem. Phys. 102, 774 (1995)]. The OH reagent is initially considered in the rovibrational state ν = 0, j = 0 and wave packet calculations have been performed for selected total angular momentum, J = 0, 10, 20, 30, 40,...,120. Converged integral state-to-state cross sections are obtained up to a collision energy of 0.5 eV, considering a maximum number of eight helicity components, Ω = 0,...,7. Reaction probabilities for J = 0 obtained as a function of collision energy, using the wave packet method, are compared with the recently published time-independent quantum mechanical one. Total reaction cross sections, state-specific rate constants, opacity functions, and product state-resolved integral cross-sections have been obtained by means of the wave packet method for several collision energies and compared with recent quasi-classical trajectory results obtained with the same potential energy surface. The rate constant for OH(ν = 0, j = 0) is in good agreement with the previous theoretical values, but in disagreement with the experimental data, except at 300 K.     

Low-energy rotational inelastic collisions of H(+) + CO system

The quantum mechanical state-to-state rotational excitation cross sections have been computed using the ab initio ground electronic state potential energy surface of the system [M. Mladenovic and S. Schmatz, J. Chem. Phys. 109, 4456 (1998)] computed at coupled-cluster single and double and triple perturbative excitations method using correlation-consistent polarized valence quadruple zeta basis set where the asymptotic potential have been computed using the dipole moment, quadrupole moment, and the molecular polarizability components and fitted to this interaction potential. The anisotropy of the surface has been analyzed in terms of the multipolar expansion coefficients for the rigid-rotor surface. The integral cross sections for rotational excitations have been computed by solving close-coupled equations at very low collision energies (5-200 cm(-1)) and the corresponding rates have been obtained for a range of low temperatures (5-175 K). The j = 0 → j(') = 1 rotational excitation cross section (and rate) is found to be the dominant followed by the j = 0 → j(') = 2 in these collision energies. The close-coupling, coupled-state, and infinite-order sudden approximations coupling calculations have been performed in the energy range of 0.1-1.0 eV using vibrational ground potential. The rotational cross sections have been obtained by performing computationally accurate close-coupling calculations at 0.1 eV using vibrationally averaged potential (ν = 1) and compared with the results of vibrational ground potential.     

Fully converged sudden rotation total integral cross sections for 4He + H2 (ν = 0, j = 0) → 4He + H2 (ν′ = 1, j′)

Total integral cross sections for ⁴He + H₂ (ν = 0, j = 0) → ⁴He + H₂ (ν′ = 1, j′ = 0, 2) have been calculated in the total energy range 1.2 to 5.5 eV, according to a quantal sudden approximation for the H₂ rotational degrees of freedom and a close coupling expansion of the vibrational degree of freedom. Convergence of the above cross sections is investigated by employing four vibration basis sets in the close coupling calculations, i.e., ν = 0,1, ν = 0,1, 2, ν = 0, 1, 2, 3 and ν = 0, 1, 2, 3, 4. Between 4.2 and 5.5 eV calculations were done with three vibration basis sets; ν = 0.–4, ν = 0–5, and ν = 0–6. It is found that at least four vibrational basis functions are needed to converge (to within 5–10%) these cross sections in the above energy range. Comparison of breathing sphere calculations and summed sudden rotation results shows good agreement for the (weakly anisotropic) Mies-Krauss potential. However, as expected the former results underestimate the vibrational 0 → 1 total integral cross sections.     

A semiclassical model of polarisation forces in atomic scattering

Low-energy elastic, differential and integral, collision cross sections for electron scattering from rare gas atoms are calculated using a simplified model treatment of the short-range polarisation forces already applied successfully to helium atoms (De Fazio et al., 1994). Static and exchange contributions to the total interaction are treated exactly, while a global semiclassical model provides a simple procedure for the short-range damping of all the long-range adiabatic terms which asymptotically lead to the polarisation forces. The results are compared with several available experimental findings for Ne and Ar atoms. The higher order terms in the perturbation expansion are found to have little effect on the cross sections and then only at low energies and in the small-angle region.Von Humboldt Stiftung Forschungspreisträger (1992)     

Accurate quantum wave packet calculations for the F + HCl → Cl + HF reaction on the ground 1(2)A' potential energy surface

We present converged exact quantum wave packet calculations of reaction probabilities, integral cross sections, and thermal rate coefficients for the title reaction. Calculations have been carried out on the ground 1(2)A' global adiabatic potential energy surface of Deskevich et al. [J. Chem. Phys. 124, 224303 (2006)]. Converged wave packet reaction probabilities at selected values of the total angular momentum up to a partial wave of J = 140 with the HCl reagent initially selected in the v = 0, j = 0-16 rovibrational states have been obtained for the collision energy range from threshold up to 0.8 eV. The present calculations confirm an important enhancement of reactivity with rotational excitation of the HCl molecule. First, accurate integral cross sections and rate constants have been calculated and compared with the available experimental data.     

Quantum scattering and adiabatic channel treatment of the low-energy and low-temperature capture of a rotating quadrupolar molecule by an ion

The capture rate coefficients of homonuclear diatomic molecules (H(2) and N(2)) in the rotational state j=1 interacting with ions (Ar+ and He+) are calculated for low collision energies assuming a long-range anisotropic ion-induced dipole and ion-quadrupole interaction. A comparison of accurate quantum rates with quantum and state-specific classical adiabatic channel approximations shows that the former becomes inappropriate in the case when the cross section is dominated by few partial contributions, while the latter performs better. This unexpected result is related to the fact that the classical adiabatic channel approximation artificially simulates the quantum effects of tunneling and overbarrier reflection as well as the Coriolis coupling and it suppresses too high values of the centrifugal barriers predicted by a quantum adiabatic channel approach. For H2(j=1)+Ar+ and N(2)(j=1)+He+ capture, the rate constants at T-->0 K are about 3 and 6 times higher than the corresponding values for H2(j=0)+Ar+ and N(2)(j=0)+He+ capture.     

An experimental and quasiclassical trajectory study of the rovibrationally state-selected reactions: HD+(v=0-15,j=1)+He-->HeH+(HeD+)+D(H)

The absolute integral cross sections for the formation of HeH+ and HeD+ from the collisions of HD+(v,j=1)+He have been examined over a broad range of vibrational energy levels v=0-13 at the center-of-mass collision energies (ET) of 0.6 and 1.4 eV using the vacuum ultraviolet (VUV) pulsed field ionization photoelectron secondary ion coincidence method. The ET dependencies of the integral cross sections for products HeH+ and HeD+ from HD+(v=0-4)+He collisions in the ET range of 0-3 eV have also been measured using the VUV photoionization guided ion beam mass spectrometric technique, in which vibrationally selected HD+(v) reactant ions were prepared via excitation of selected autoionization resonances of HD. At low total energies, a pronounced isotope effect is observed in absolute integral cross sections for the HeH++D and HeD++H channels with significant favoring of the deuteron transfer channel. As v is increased in the range of v=0-9, the integral cross sections of the HeH++D channel are found to approach those of HeD++H. The observed velocity distributions of products HeD+ and HeH+ are consistent with an impulsive or spectator-stripping mechanism. Detailed quasiclassical trajectory (QCT) calculations are also presented for HD+(v,j=1)+He collisions at the same energies of the experiment. The QCT calculations were performed on the most accurate ab initio potential energy surface available. If the zero-point energy of the reaction products is taken into account, the QCT cross sections for products HeH+ and HeD+ from HD+(v)+He are found to be significantly lower than the experimental results at ET values near the reaction thresholds. The agreement between the experimental and QCT cross sections improves with translational energy. Except for prethreshold reactivity, QCT calculations ignoring the zero-point energy in the products are generally in good agreement with experimental absolute cross sections. The experimental HeH+/HeD+ branching ratios for the HD+(v=0-9)+He collisions are generally consistent with QCT predictions. The observed isotope effects can be rationalized on the basis of differences in thermochemical thresholds and angular momentum conservation constraints.