N9H9链状异构体的结构与稳定性的理论研究

采用密度泛函理论(DFT)B3LYP方法,在6-311＋＋G**基组水平上对N9H9可能存在的链状构型进行了几何优化,得到46种稳定链状异构体。应用自然键轨道理论NBO和分子中的原子理论AIM分析了这些化合物的成键特征和相对稳定性,G3MP2方法计算了各异构体的精确能量及在298K时的生成热ΔfHө(298K),并计算了由Peter Politzer等人所介绍的相对比冲量。研究结果表明：各异构体中N原子孤对电子与N＝N形成了p→π共轭作用是影响双键相邻的N－N键长变化的主要原因,并且对异构体的稳定性起着重要作用。所有异构体中N＝N位于链端的稳定性较差,其中B9最稳定, B6稳定性最差;C5是所有异构体中生成热最大的,也是相对比冲量最大的。     

从头计算研究1-甲基-次黄嘌呤的电离能

采用从头计算B3LYP/Aug-cc-pVDZ方法研究了1-甲基-次黄嘌呤最稳定的六种可变异构体. 两种异构体N7H 和N9H有着相当的能量,远比其它异构体稳定. 理论计算了各种可变异构体的转动常数和偶极矩. 运用电子传播子理论P3近似方法计算稳定异构体外价壳层轨道的电离能,计算结果与光电子能谱实验结果符合较好. 根据异构体的相对能量以及理论模拟电离能谱和实验光电子能谱之间的比较,说明在气相光电子能谱实验中至少存在两种可变异构体.     

HFSiS构型及其稳定性的理论研究

利用密度泛函理论对三线态HFSiS分子结构及其稳定性进行了详细的理论研究.在B3LYP/6-311G**水平上计算出了各驻点的优化构型、振动频率,并对各个振动模式加以归属,在同样的理论水平上进行了IRC计算;CCSD(T)结合6-311G**基组对于驻点进行单点能及相对能量的计算;根据振动模式分析来阐明三线态势能面上各驻点之间的变化,并与单线态势能面进行比较.计算结果表明,三线态HFSiS分子存在6种异构体,3HFSiS结构在动力学和热力学上都是最稳定的,实验上应该可以观测到;在两组键旋转异构体当中,结构-2具有一定的动力学稳定性,而结构-1动力学稳定性较差;3SiSHF在动力学上和热力学上都是最不稳定的结构.     

6-硫代鸟嘌呤磺化异构体热力学稳定性的计算研究

采用量子化学密度泛函理论B3LYP方法在6-311++G(d,p)基组水平上,对6-硫代鸟嘌呤硫醇式与硫酮式两类共14种磺化异构体的热力学稳定性进行了计算研究,全自由度优化了各物种构型,进行了振动分析,获得了各磺化异构体的零点能、焓、热力学能以及吉布斯自由能等热力学数据.分析了各异构体磺化前后稳定性的变化情况,探讨了磺化异构体的稳定性问题.结果表明,不论是硫酮式还是硫醇式磺化异构体,当H原子连接到N7上时磺化异构体稳定性均比连接到N9上时较高一些.在6-硫代鸟嘌呤磺化异构体中,STG(3,7,10,10)是最稳定的异构体,STG(1,7,10,10)、STG(1,9,10,10)和STG(1,3,7,10)等异构体也可共存,其他异构体存在的可能性均较小.     

环状氮氢化合物NnHn(n=3~5)的构象研究

应用密度泛函理论对10种环状氮氢化合物异构体进行了研究.利用自然键轨道理论(NBO)和分子中的原子理论(AIM)分析了这些异构体的成键特征、相对稳定性.N-N键长与键临界点的电荷密度存在反比关系.超共轭作用和立体排斥作用计算表明:立体排斥作用和超共轭作用在决定构象稳定性的方面均起了主要的作用.H原子的相对位置的差异影响了键-键立体排斥能的类型.     

N4H4分子取代基效应的量子化学研究

本文计算了甲基（-CH₃）,羟基（-OH）对1-丁氮烯和2-丁氮烯的取代基效应.1-丁氮烯引入取代基后.N=N双键的键长变短,而N-N单键的键长增长.异构体2-丁氮烯的键长变化较小.引入甲基或羟基后,N原子的孤对电子会与相应的N-C（N-O）键之间发生相互作用,使整个分子的超共轭作用增强.随着取代基数目的增多,总能量和生成热就会降低,取代基数目与分子能量（生成热）之间具有很好的相关性.     

Si6N2团簇结构与性质的密度泛函理论研究

用密度泛函理论(DFT)中的杂化密度泛函B3LYP方法,在6-31G(d)的水平上对Si6N2团簇的可能结构进行了几何结构优化和电子结构计算,得到了16个可能的异构体.Si6N2团簇的最稳定结构是有4个Si-N键和4个Si-Si键的三维结构.自然键轨道方法分析成键性质的结果表明,Si-N键中Si原子向N原子有较大的电荷转移,因此Si-N原子间有较强的电相互作用;最强的IR和Raman谱峰分别位于1359.14cm-1和1366.29cm-1处;并计算了Si6N2团簇的最稳定结构的极化率和超极化率.     

环状氮氢化合物NnHn(n=3~5)的构象研究

应用密度泛函理论对10种环状氮氢化合物异构体进行了研究。利用自然键轨道理论(NBO)和分子中的原子理论(AIM)分析了这些异构体的成键特征、相对稳定性。N-N键长与键临界点的电荷密度存在反比关系。超共轭作用和立体排斥作用计算表明:立体排斥作用和超共轭作用在决定构象稳定性的方面均起了主要的作用。H原子的相对位置的差异影响了键-键立体排斥能的类型。     

CuSi6团簇几何结构和性质的密度泛函理论研究

利用密度泛函理论（DFT）的B3LYP方法,采用全电子基组6-311+G（d）研究了CuSi₆团簇的几何构型和电子结构性质,计算表明CuSi₆团簇存在多个能量相近的稳定异构体,且结构中存在多个Cu-Si键,多个低能异构体共存解释了实验中观察到的CuSi₆团簇较强的现象.对于CuSi₆团簇,计算得到的三个最稳定异构体的垂直电离能,电子亲和能和HOMO-LUMO能隙均相对较大,也表明这三个异构体较为稳定.     

N4H4分子取代基效应的量子化学研究

本文计算了甲基(-CH3),羟基（-OH）对1-丁氮烯和2-丁氮烯的取代基效应。当1-丁氮烯引入取代基后,N=N双键的键长变短,而N-N单键的键长增长。异构体2-丁氮烯的键长变化较小。当引入甲基或羟基后,N原子的孤对电子会与相应的N-C(N-O)键之间发生相互作用,使整个分子的超共轭作用增强。随着取代基数目的增多,总能量和生成热就会降低,取代基数目与分子能量（生成热）之间具有很好的相关性。     

Nature of resonance states in the 9Be and 9B mirror nuclei

The spectra of low-lying states of the ⁹Be and ⁹B mirror nuclei in the excitation-energy range between 0 and 5 MeV are considered within the microscopic α + α + n(p) three-cluster model, which is a three-cluster variant of the algebraic version of the resonating-group method. Attention is given primarily to studying the nature of resonance states in a three-cluster continuum. A detailed comparison of the results obtained in this way with experimental data and with results of other microscopic calculations is performed.     

Étude géométrique du monopole magnétique

Le mouvement d'une particule chargée soumise au champ d'un monopole magnétique est étudié dans un cadre géométrique.

Le formalisme sans corde de Wu et de Yang permet d'interprêter géométriquement la symmétrie de rotation mais s'avére insuffisant pour traiter les symétries cachées découvertes récemment par Jackiw. Cette tache est accomplie par la quantification géométrique de Souriau et de Kostant. La relation des deux constructions est expliquée en détail.     

On the structure of9He nucleus

The comparison of the calculated widths of⁹He with the measured ones shows that: 1) the shell occupation in⁹He has a normal order (1/2^?-1/2⁺) contrary to some shell model predictions of the parity inversion; 2) strong core polarization in⁹He takes place which explains the existence of narrow levels in⁹He and their absence in⁷He.     

Cross section measurements for the 9Be+9Be System at subbarrier energies

The total reaction cross section and the characteristic y-ray cross sections have been measured for the ⁹Be+ ⁹Be reaction in the energy range E_cm = 1.4–3.4 MeV, detecting the prompt γ-rays emitted by the various residual nuclei with two Nal detectors in nearly 4π geometry and with a germanium detector, respectively. The differential elastic cross sections for the same system have also been measured at e_c.m.= 2.2, 2.7 and 3.2 MeV. The cross sections calculated with the “standard” and the proximity optical model potentials, which describe well the total reaction cross sections of the light nuclei, agree with the ⁹Be + ⁹Be elastic-scattering data, but underpredict the total reaction cross section by a factor of 2 to 3. The characteristic γ-ray measurements show that all two-particle emission channels, nα ¹³C, nn¹⁶O, np¹⁶N and αα¹⁰Be are enhanced by about that factor, while the single-particle emission channel, p¹⁷N, is not enhanced.     

The first excited states of 9Be and 9B

It is found here that the 1/2⁺ first excited state of ⁹Be is a virtual state with the energy of −23.5 KeV. The line shape for the excitation of the state is approximated with a simple analytic form based on the effective range expansion. The partner in ⁹B of this state is found to be a resonance with a maximum in the peak at about 1.1 MeV, FWHM of 1.5 MeV, and complex energy of 0.6 −i0.75 MeV. The line shape for its excitation is calculated in terms of the p−⁸Be phase shift. The phase shifts are obtained from N−⁸Be effective potentials deduced from the data on the photodisintegration of ⁹Be. A possibility for direct extraction of the energy of the resonant state from experimental data is also discussed, and an expression for a residue at a virtual state pole in terms of a quadrature taken over the virtual state eigenfunction is given. Received: 23 March 1998 / Revised version: 3 September 1998     

Quasi-optical assessment of the ALMA band 9 front-end

The ALMA band 9 (600–720 GHz) receiver is a dual channel heterodyne system which is capable of detecting orthogonally polarised signals utilising a wire grid beam splitter. Two Superconductor–Insulator–Superconductor (SIS) mixers mounted behind hybrid mode corrugated horns are coupled to the 12 m Cassegrain antenna via a wavelength independent configuration of two off-axis elliptical mirrors.We outline an approach involving accurate physical optics simulations in conjunction with precise experimental measurements of the complete optical front-end which guarantees the highest performances. This practical verification approach can be generalised to all quasi-optical receivers to validate system performance. In this paper, we verify the optical design and estimate antenna system efficiency. Comparison between measurement and simulation indicates precise information is achievable in estimating system performance allowing potential improvements in ALMA instrument calibration accuracy.     

Spectroscopy of9He with the (13C,13O)-reaction on9Be

First results of the double-charge-exchange reaction⁹Be(¹³C,¹³O)⁹He, E_Lab=380 MeV, are presented. The ground state and an excited state at 3.8 MeV are clearly seen. A preliminary value of the⁹He mass excess is obtained: 41.5±0.6 MeV. Spectra of of the⁹Be(¹³C,¹⁴O) He-reaction have been measured with high resolution. The ground state transition appears as a pronounced sharp peak, but no other narrow peaks are observed.     

Quadrupole interaction of8Li and9Li in LiNbO3 and the quadrupole moment of9Li

The quadrupole interaction of nuclear spin polarized⁸Li (I=2) and⁹Li (I=3/2) in LiNbO₃ has been studied at room temperature. The polarization was achieved by optical pumping of a fast atomic beam with circularly polarized laser light. The atoms were implanted into a hexagonal LiNbO₃ single crystal and the quadrupole splitting ofβ-NMR spectra was measured. A ratio of ¦Q(⁹Li)/Q(⁸Li)¦=0.88(4) for the nuclear quadrupole moments was deduced, yielding a new value of ¦Q(⁹Li)¦=25.3 (9) mb for the quadrupole moment of⁹Li.