Effect of molecular structure on fragmentation of isolated organic molecules in solid rare gas matrices

The effect of excess energy on the primary radical cations of bifunctional carbonyl compounds and aliphatic alkynes was simulated by matrix isolation method using rare gas matrices with various ionization potentials. The formation of fragmentation products was monitored by EPR and FTIR spectroscopy. It was shown that the radical cations of bifunctional compounds (CH₃OCH₂COCH₃ and CH₃COCOCH₃) dissociated effectively yielding CH₃ radicals upon irradiation in solid argon matrix at T≤16 K. In addition to isolated methyl radicals, the radical pairs consisting of two methyl radicals separated by two CO molecules were detected in the case of diacetyl. The probability of fragmentation decreases with the decreasing excess energy by switching from Ar to Xe. In general, bifunctional molecules were found to be less stable to “hot” ionic fragmentation in low-temperature solids in comparison with simple prototype compounds. In the case of alkynes of the RCCH type, a noticeable yield of fragmentation products was observed when R=–C(CH₃)₃, but it was negligible for R=–CH₃. The mechanisms of “hot” reactions and excess energy relaxation are discussed.     

Rotation of an elastic sphere about its mass center in the gravitational field of two attracting points

A planet model as a uniform elastic sphere in the gravitational field of two mass points whose mutual motion causes tidal deformations is considered. The sphere rotation about its mass center is studied with consideration of its deformations caused by the centrifugal force field and the gradient fields of gravitational forces. The sphere’s inertia tensor whose components are time dependent is found. The sphere’s angular velocity projections onto the axes associated with the sphere according to an integral law are determined. The results obtained are illustrated for the case of the Earth. For this case, the equivalent values of the elasticity modulus and Poisson’s ratio and the angular velocity disturbances are found.     

泥沙输运模拟综述——现状及其发展趋势

随着流体力学中数值方法的飞速发展,计算模型已经成为研究流体运动,泥沙输运和不同环境(诸如河流,湖泊及沿海地区)中相应污染物归趋过程等方面非常有吸引力的工具,在过去的30多年里,发展了许多计算水动力学/泥沙输运模型.文章追溯当前具有代表性的(一维、二维、三维)模型的发展历程,描述他们各自的特点,优势及局限,力图作为对模型方面感兴趣读者的第一指南,同时也为大家讨论模型的局限性,未来的发展趋势和研究需求方面搭建一个平台.给出了模型的表达,时空特性,水动力学和沉积物的耦合方式,处理非恒定流,推移质和悬移质,泥沙交换过程,泥沙类型(粘性或非粘性)及非均匀泥沙输运的能力.总结了不同模型的应用实例,读者可以运用这些例子作为研究模型设置,模型率定及模型验证的参考.给出了选择泥沙输运模型应遵循的原则,模型输入及率定方面存在的问题及改进的途径.探讨了现有水动力学/泥沙输运模型在处理复杂湍流,泥沙携带,流动与输沙耦合,非均匀泥沙,离散和扩散系数,河岸来沙处理等方面的局限性及改进的方向.最后,对基于多相流思想的泥沙输运模型及其它一些交叉性问题作了评述与展望.     

Positive hole transfer between organic molecules of different classes in freon matrices

The processes of positive charge (hole) transfer between organic molecules of different classes occurring upon irradiation of their frozen freonic solutions at 77 K were studied by ESR spectroscopy. The efficiency of positive hole transfer was characterized by the “redistribution coefficient”, which was determined as ratio of concentrations of the radical cations of different compounds at equal concentrations of the parent neutral molecules. A very effective positive hole transfer to toluene was shown to occur for alkane-toluene pairs (K > 10). Meanwhile, much lower K values (～ 2 to 3) were observed for alkane-alkene pairs, in spite of a rather high difference in the ionization potentials (ca. 1 eV). This effect was explained by the conformation dispersion and distribution of environment configurations of ionized molecules for the alkane-alkene pairs. An effective positive hole transfer (K ～ 6) was observed for the pair dimethyl ether-acetone, where the conformation dispersion was absent, although the difference in ionization potentials for this pair was only 0.3 eV.     

Study of aberration correction in two types of electrostatic lenses

A detailed comparative study is carried out of chromatic and spherical aberration in a crossed lens and in a lens formed by four cylindrical electrodes, the two inner ones of which are cut into four symmetrical longitudinal sections. The study was performed by numerical modeling. The possibility of simultaneous correction of both types of aberration in a linear image is demonstrated. A comparison is made with an equivalent axisymmetric lens. Zh. Tekh. Fiz. 67, 92–96 (August 1997)     

On the spectral height of F-compact spaces

We prove that given an ordinal α with 0 < α ≤ ω ₁ and α ≠ β+1, where β is a limit ordinal, there exists an F-compact space of spectral height α.     

Relative rate constants for the reactions of trichloropropenyl radical. Application of the two-parameter Taft equation

The relative rate constants for the hydrogen atom abstraction by CCl₃CH?CH· radical from CH₂Cl₂, CHCl₃, CH₃COCH₃, CH₃CN, C₆H₅CH₃, C₆H₅OCH₃, CH₃CHO, and CH₃OH in the liquid phase at 20°C have been measured. It was shown that these reaction rate constants are correlated by the two-parameter Taft equation with ρ* = 0.726 ± 0.096, r* = 1.22 ± 0.16. A relationship between r* and bond dissociation energy D(R? H) has been found for the abstraction reactions of different free radicals.