Rare earth photoionization study by the resonant microwave cavity technique

Photoconductivity spectra of rare earth-doped insulating materials are measured using the resonant microwave cavity method. This technique is based on the detection of the cavity Q-factor changes induced by irradiation of the sample (inserted in the cavity) by a pulsed tunable laser. Results obtained with Lu₂(SiO₄)O:Ce³⁺ and BaF₂:Eu²⁺ are presented and discussed. Photoionization thresholds at 400 nm (3.1 eV) and 310 nm (4.0 eV) are measured for Lu₂(SiO₄)O:Ce³⁺ and BaF₂:Eu²⁺, respectively.     

二溴甲烷的同步辐射光电离研究

采用５０～２００ｎｍ同步辐射光，对ＣＨ２Ｂｒ２的光电离过程进行了研究，根据测定的母体离子及其碎片离子出现势，得到二溴甲烷的绝热电离势为１０．２３±０．０１ｅＶ，并获得了离子的生成焓，解离能及键能等热力学数据，分析了碎片离子的光解离电离通道。     

Si(CH3)2Cl2分子的电离电势和化学键能的测定

有机硅化合物是半导体工业中产生硅元件的基本原料和有机合成中的重要试剂，是多年来大家研究较多的分子体系之一．本文报导了用同步辐射加速器产生的真空紫外光，电离St（CH3hCI。分子．在50－120n－m波长范围内，测量了各种离子产物与真空紫外光波长的关系，推算得它的绝热电离电势和离子中几个化学键的键能．1实验装置和方法本工作在国家同步辐射实验室光化学实验站进行．进行分子真空紫外光电离研究的实验系统已在文献山中详细描述．同步辐射加速器产生的真空紫外光波长用Ne气的电离势标定，其误差＜士0－Inln．单色仪的分辨率为河凸…     

Vacuum Ultraviolet Free-Electron Laser Photoionization Mass Spectrometry of Alpha-pinene Ozonolysis

\begin{document}$\alpha$\end{document}-pinene is the most abundant monoterpene that represents an important family of volatile organic compounds. Molecular identification of key transient compounds during the \begin{document}$\alpha$\end{document}-pinene ozonolysis has been proven to be a challenging experimental target because of a large number of intermediates and products involved. Here we exploit the recently developed hybrid instruments that integrate aerosol mass spectrometry with a vacuum ultraviolet free-electron laser to study the \begin{document}$\alpha$\end{document}-pinene ozonolysis. The experiments of \begin{document}$\alpha$\end{document}-pinene ozonolysis are performed in an indoor smog chamber, with reactor having a volume of 2 m\begin{document}$^3$\end{document} which is made of fluorinated ethylene propylene film. Distinct mass spectral peaks provide direct experimental signatures of previously unseen compounds produced from the reaction of \begin{document}$\alpha$\end{document}-pinene with O\begin{document}$_3$\end{document}. With the aid of quantum chemical calculations, plausible mechanisms for the formation of these new compounds are proposed. These findings provide crucial information on fundamental understanding of the initial steps of \begin{document}$\alpha$\end{document}-pinene oxidation and the subsequent processes of new particle formation.     

Donor impurity-related photoionization cross-section in parabolic quantum wires: Effects of intense laser field and applied electric field

Within the effective mass approximation, the effects of the electric and intense laser fields on the binding energy and the photoionization cross-section of shallow-donor impurities in GaAs/GaAlAs parabolic quantum wires are investigated theoretically by using a variational method. The numerical results show that the electric and intense laser fields lead to significant changes in the binding energy and photoionization cross-section.     

NH3的同步辐射光电离

用同步辐射光在１０．０－１１．８ｅＶ能量范围内测量了ＮＨ３的光电离效率曲线，观察到在台阶状的离子振动谱上叠加了丰富的自电离结构。通过相应振动结构分析，得到ＮＨ３分子离子基电子态的振动波数ωｅ和非谐性常数（ωｅχｅ），对于出现的自电离结构可归类于ｎｓａ１（ｎ＝５，６），ｎｐａ１（ｎ＝５，６）和ｎｐｅ（ｎ＝６，７）Ｒｙｄｂｅｒｇ系列。     

Resonant widths, line intensities and lineshapes for MQDT models with two or more open channels

Approximate analytical formulae describing the energy variation of line intensities, autoionization widths and lineshape asymmetries, are derived for a Phase-Shifted Multichannel Quantum Defect Theory model composed of two closed interacting channels coupled to two effective continua. This is accomplished by putting the two compatibility equation solutions, for the common phase shifts of the two open channels, in such a form so the resonant behavior is attributed to one of them, the other accounting for an energy dependent background. Then, the well-known procedures for the simpler case where only one continuum is considered are applied, using only the resonant solution. The method is quite general and applicable to any MQDT model with two or more open channels. The resulting analytical formulae are tested on experimental spectra of Sr, Ba and Cu and it is shown that they are valid as long as: i) The resonances are non-overlapping, ii) The direct closed channel coupling is much stronger than the indirect one through the continua and (when excitation matrix elements are involved) iii) The open channels excitation strength is smaller or at least comparable to the closed channels one. Received: 26 May 1998 / Accepted: 1st July 1998     

Elliptic dichroism in hydrogen ionization by a coherent superposition of two harmonics

The two-photon ionization of the hydrogen atom from its ground state by a two-colour electromagnetic field consisting of two odd harmonics of the same IR laser is analyzed. The influence of the state of polarization of the bichromatic field on the azimuthal angular distribution and the dependence of the elliptic dichroism on the photon frequencies are reported. Received 11 December 2002 Published online 29 April 2003 RID="a" ID="a"e-mail: fritz.ehlotzky@uibk.ac.at     

A simple non-perturbative approach of atom ionisation by intense and ultra-short laser pulses

A simple theoretical approach based on Coulomb-Volkov states is introduced to predict ionisation of atoms by intense laser pulses in cases where the effective interaction time does not exceed one or two optical cycles [M. Nisoli et al., Opt. Lett. 22, 522 (1997)]. Under these conditions, the energy distributions of ejected electrons predicted by this non-perturbative approach are in very good agreement with “exact" results obtained by a full numerical treatment. The agreement is all the better that the principal quantum number of the initial state is high. For very strong fields, most electrons are ejected at an energy which is close to the classical kinetic energy that would be transferred to free electrons by the electromagnetic field during the pulse. The power of the present approach appears when keV. In this region, full numerical treatments become very lengthy and finally do not converge. However, the present Coulomb-Volkov theory still makes reliable predictions in very short computer times. Received 19 November 1999 and Received in final form 19 January 2000