Zhang Yun-Wu

Theoretical and experimental study of aluminum ion–acetonitrile clusters

Abstract The gas phase reactions between a singly charged aluminum ion and acetonitrile clusters are studied by a laser ablation-molecular beam method. Similar to metal ion–methanol clusters, two distinct intensity gaps of Al+(CHCN)n clusters are found. The first intensity gap occurs between n=4 and n=5, and the second is found between n=6 and n=7. Density functional calculations on the structures and energetic of the reactants and products are carried out at the B3LYP/6-31+G ∗ level in order to get a qualitative picture about the gross geometries and thermodynamic stability. For ionic clusters Al+(CHCN)n, there are two kinds of stable isomers. As the size of the cluster increases from two to four, the relative stability decreases gradually. According to the results of experiments, the signal intensity of clustered complex ions decreases with the size of the cluster increase from two to four. Good agreement between theory and experiment is found for ionic clusters Al+(CHCN)n.

Deuterium separation by multiphoton dissociation of dichlorofluoromethane

Absorption and dissociation probabilities of CHCl2F and CDCl2F were investigated by a pulsed CO2 laser in the wavenumber region of largest selectivity for deuterium. The absorption of CHCl2F, which is a difference band, can largely be suppressed by cooling. At 200 K and at 920 cm−1 absorption selectivities up to 4000 were found by extrapolation. In the presence of buffer gas, CDCl2F can be multiphoton excited nearly like a linear absorber (“harmonic oscillator”). This is interpreted by a nearly resonant collisional relaxation v7 to v2 and by the smallness of the cross anharmonicity x27. The dissociation selectivityS was 24,000 at natural abundance. Such large values were measured by a chromatographic method.S depends only onpD, the partial pressure of the deuterated species. This dependence is approximately ln S∝pD−1. It can be rationalized by considering only the average energy transferred to the nonresonant molecules by collisions with CDCl2F. The above functional shape is related to an Arrhenius type law. Comparison with trifluoromethane for D separation shows that CHCl2F has primarily two advantages: its rapid H-D exchange with water and the less stringent requirements of laser energy and pulse length.

The Measurement of the Ionization Potential and the Bond Energy Si(CH 3 ) 2 Cl 2

The vacuum ultraviolet photoionization spectrum of Si(CH3)(2)Cl-2 has been obtained with synchrotron radiation source. The adiabatic ionization potential of Si(CH3)(2)Cl-2 is 10.62 +/- 0.03eV (0.37eV lower than reported by PES), and the appearance potentials for Si(CH3)Cl-2(+), Si(CH3)(2)Cl+, SiCH3+ and SiCl+ are 11.25 +/- 0.03eV, 12.69 +/- 0.04eV, 15.1 +/- 0.1eV and 21.16eV +/- 0.1eV respectively. From these results, we estimate D(Si(CH3)Cl-2(+)-CH3)=0.63 +/- 0.03eV and D(Si(CH3)(2)Cl+-Cl))=2.07 +/- 0.04eV.

Linear zone plate monochromator for soft X-ray microscopy

Abstract In this article we describe the linear zone plate monochromator of the beam line BL12A at HESYRL. The monochromator will provide a monochromatic SR light source for a soft X-ray scanning microscope. It consists of four chambers that contain its optical elements. Three kinds of condenser zone plates are used as its dispersing and focusing elements and a pinhole as its exit slit. Being moved over a distance of 220 mm along the optical axis, the zone plates cover the wavelength range from 20 A to 54 A. Then a microzone plate images the monochromatic light to an ultimate spot size of 0.2 μm in a diameter at the sample.