The rotational spectrum of epifluorohydrin measured by chirped-pulse Fourier transform microwave spectroscopy

The rotational spectrum of epifluorohydrin measured by chirped-pulse Fourier transform microwave (CP-FTMW) spectroscopy is presented. A new CP-FTMW spectrometer capable of measuring the entire 7.5-18.5 GHz spectrum with a single polarizing pulse is described briefly. The CP-FTMW spectrometer takes advantage of recent advances in digital electronics by utilizing a 4.2 GS/s arbitrary waveform generator as a frequency source and a 12 GHz digital oscilloscope to digitize the down converted molecular free induction decay (FID). Signal averaging in the time domain is used to increase the signal-to-noise ratio. The rotational constants of three unique conformers of epifluorohydrin were measured, as well as the rotational constants of the three unique ¹³C isotopomers and the ¹⁸O isotopomer (in natural abundance) of the most stable conformer. The rotational constants of the two less stable conformers differ significantly from those previously reported [F.G. Fujiwara, J.L. Painter, H. Kim, J. Mol. Struct. 41 (1977) 169-175]. Ab initio calculations were performed for all three conformations and are compared to experimental values.     

Symbolic evaluation of coefficients in Airy-type asymptotic expansions

Computer algebra algorithms are developed for evaluating the coefficients in Airy-type asymptotic expansions that are obtained from integrals with a large parameter. The coefficients are defined from recursive schemes obtained from integration by parts. An application is given for the Weber parabolic cylinder function.     

可变焦列阵柱面透镜均匀线聚焦系统

用两个列阵柱面透镜与非球面透镜组成变焦线聚焦系统，能将入射激光束会聚成辐照均匀、长度连续可调的焦线，它可用于Ｘ光激光实验研究．文中详细分析了焦线上光场分布的情况，给出了物理光学分析的结果，并与巳有技术作了比较．     

Thiophenol and thiophenol radical and their complexes with gold clusters Au5 and Au6

The longstanding controversy between experiment and theory regarding which conformer of thiophenol, planar or perpendicular, is the most stable and what is the magnitude of the corresponding rotational barrier of the S–H group is discussed. We propose a variety of rather modest high-level computational methods within the density theory, which corroborate the experimental data. These methods demonstrate that the planar structure of thiophenol is the most stable and the magnitude of the rotational barrier falls within the experimental range of 3.35±0.84 kJ mol⁻¹. However, the barrier is of the order of RT at room temperature, which might prevent to clearly identify the most stable conformer of thiophenol in experiments and leads to a large-amplitude motion of the thiolic hydrogen. On the other hand, such low value of the barrier may lead to some error in evaluating the thermodynamic properties of thiophenol within the rigid-rotor-harmonic oscillator model, in particular for the bond dissociation enthalpy. We also show the existence of a large entropy contribution to the Gibbs free energy difference between the planar and perpendicular conformers which is the order of the rotational barrier (≈4 kJ mol⁻¹). This might be of interest for experimental study. The most stable complexes of thiophenol with the gold clusters Au₅ and Au₆ are also investigated. It is shown that the sulfur atom prefers to anchor to two- and three-coordinated atoms of gold in these clusters to form a strongly directional gold–sulfur bond. The hydrogen abstraction from the S–H group of thiophenol bonded to the two-coordinated gold atom in Au₅ yields the bridging Au–S dibond and results in a spectacular reduction of the bond dissociation energy of thiophenol by nearly a factor of three.     

Numerical exploration of new features on three-dimensional transition of a cylinder wake

The three-dimensional transition of the wake flow behind a circular cylinder is studied in detail by direct numerical simulations using 3D incompressible N-S equations for Reynolds number ranging from 200 to 300. New features and vortex dynamics of the 3D transition of the wake are found and investigated. At Re = 200, the flow pattern is characterized by mode A instability. However, the spanwise characteristic length of the cylinder determines the transition features. Particularly for the specific spanwise charac-     

Vibrations of a piezoceramic cylinder subject to nonstationary electric excitation

The paper proposes a method to solve the problem of vibrations of a radially polarized piezoelectric cylinder subject to nonstationary electric excitation. The dynamic electromechanical state of the cylinder is analyzed. The time-dependences of electric and mechanical characteristics are plotted. The distribution of these characteristics over the cross section of a short cylinder is examined. The region of end disturbances in a long cylinder is identified __________ Translated from Prikladnaya Mekhanika, Vol. 43, No. 3, pp. 73–79, March 2007.     

2-D/3-D finite-element solution of the steady Euler equations for transonic lifting flow by stream vector correction

In this paper we study the validation of the new formulation (potential-stream vector) of the steady Euler equations in 2-D/3-D transonic lifting regime flow. This approach, which is based on the Helmholtz decomposition of a velocity vector field, is designed to extend the potential approximation of Euler equations for severe situations such as high transonic or rotational subsonic flows. Different results computed by a fixed point algorithm on the stream vector correction are shown and discussed by comparing them with those obtained by the full potential approach.     

Laser Spectroscopy on the MgH A2Π - X2Σ+ Band System

The A²Π - X²Σ⁺ electronic transition of MgH has been studied by the laser excitation spectroscopy. Some new transitions have been observed for the first time. Rotational parameters of the X and A state have been derived and compared with other experimental values.     

转动传能中的量子干涉--干涉角和转动量子数的关系

沙国河等人在CO(A1∏(v=0)~e3∑-(v=1))体系与He,Ne和Ar碰撞诱导转动传能中首次观测到了量子干涉效应,并测量了干涉度。从理论上进一步研究原子-双原子分子体系碰撞诱导转动传能中量子干涉效应与转动量子数以及能量间隔的关系是十分必要的。我们考虑长程相互作用势,应用一级玻恩近似和直线轨迹近似,分别计算了CO(A1∏(v=0)~e3∑-(v=1))体系和He,Ne,Ar碰撞诱导转动传能中不同转动量子数以及不同能量间隔下的干涉角,得到了干涉角随转动量子数和能量间隔的变化趋势。这些结果对设计、分析这种类型的实验有一定的指导意义。     

Wave Motions in a Two-Layer Fluid Driven by Small Oscillations of a Cylinder Intersecting the Interface

The plane problem of steady-state small oscillations of a horizontal cylinder located at the interface between two fluids of different densities and indefinite depth is considered in the linear formulation. Boundary integral equations for the surface source distribution are derived. The behavior of the distributed singularities at points of intersection of the body contour and the interface is investigated. The problem of oscillations of a circular cylinder is solved by the multipole expansion method. The apparent mass and damping coefficients of the radiation problem and the reflection coefficient of the problem of scattering of an impinging wave by a floating body are calculated.