Simulation of two-photon-photoelectron spectra at a jellium-vacuum interface

In this paper we report on time dependent configuration interaction singles (TD-CIS) calculations aimed at simulating two-photon-photoelectron emission (2PPE) spectra of metal films, the latter treated within a one-dimensional jellium model. The method is based on a many-electron approach in which electron-electron-scattering is approximately accounted for and no artificial lifetimes have to be assumed for excited electrons. This contrasts with one-electron models where lifetimes and dissipation have to be introduced. The driving force for the photoelectron ejection in 2PPE experiments is the electric field of two laser pulses that are generally separated by a delay time, t. To compute energy- and time-resolved 2PPE signals P(E,t), a new scheme based on the time-energy method is proposed to analyze electronic wave packets in asymptotic regions of the potential. PACS 78.20.Bh; 79.60.Bm     

VUV-heating of plasma layers and their use as ultrafast switches

We report on new possibilities to generate solid-density plasma at extreme energy density by intense VUV beams. Here we consider 100 fs pulses of 30 eV photons focused to 10¹⁶ and 10¹⁸ W/cm². The temperature evolution in 50 nm thick aluminum foils is discussed on the basis of simulations, performed with the one-dimensional radiation hydrodynamics code MULTI-fs. For 30 eV photons, the foil is shown to switch from transmission to reflection mode on a femto-second time-scale; this is due to the rapid change of the plasma frequency during laser heating which may turn an initially transparent Al-foil into an opaque one. The switching-time depends on the intensity of the laser pulse. Also layered heating structures inside the foil are discussed which occur due to reflection at the rear surface.     

Faraday instability in a surface-frozen liquid

Faraday surface instability measurements of the critical acceleration, a(c), and wave number, k(c), for standing surface waves on a tetracosanol (C24H50) melt exhibit abrupt changes at T(s)=54 degrees C, approximately 4 degrees C above the bulk freezing temperature. The measured variations of a(c) and k(c) vs temperature and driving frequency are accounted for quantitatively by a hydrodynamic model, revealing a change from a free-slip surface flow, generic for a free liquid surface (T>T(s)), to a surface-pinned, no-slip flow, characteristic of a flow near a wetted solid wall (T相似文献   

Precision Rosenbluth measurement of the proton elastic form factors

We report the results of a new Rosenbluth measurement of the proton electromagnetic form factors at Q2 values of 2.64, 3.20, and 4.10 GeV2. Cross sections were determined by detecting the recoiling proton, in contrast to previous measurements which detected the scattered electron. Cross sections were determined to 3%, with relative uncertainties below 1%. The ratio mu(p)G(E)/G(M) was determined to 4%-8% and showed mu(p)G(E)/G(M) approximately 1. These results are consistent with, and much more precise than, previous Rosenbluth extractions. They are inconsistent with recent polarization transfer measurements of similar precision, implying a systematic difference between the techniques.     

Femtosecond formation of coupled phonon-plasmon modes in InP: Ultrabroadband THz experiment and quantum kinetic theory

The ultrafast transition of an optical phonon resonance to a coupled phonon-plasmon system is studied. After 10-fs photoexcitation of i-InP, the buildup of coherent beats of the emerging hybrid modes is directly monitored via ultrabroadband THz spectroscopy. The anticrossing is mapped out as a function of time and density. A quantum kinetic theory of microscopic carrier-carrier and carrier-LO-phonon interactions explains the delayed formation of the collective modes. The buildup time is quantitatively reproduced to scale with the oscillation cycle of the upper branch of the coupled resonance.     

Analysis of volatile halogenated hydrocarbons on the ppq scale

Summary The use of volatile halogenated hydrocarbons in manufacturing and industry has turned these substances into a severe problem for our environment. Therefore, industries and environmental protection agencies have become very interested in a rapid and trace-scale analysis of these compounds. Investigations have therefore been undertaken on the separation of such components by means of GC-ECD and GC-MS, respectively. The applicability of the analysis system elaborated is demonstrated for actual water samples and biological materials.

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Analyse von flüchtigen halogenierten Kohlenwasserstoffen im ppq-Bereich

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Parts of this work were presented at the 7. Österreichische Chemietage, Vienna, 3–6 Nov. 1987     

Hydrogen-bonded complex between HNO and formaldehyde. Photolysis of methyl nitrite in an argon matrix

Nitroxyl and formaldehyde have been prepared by photolyzing methyl nitrite and six of its isotopomers in an argon matrix at low temperature. Under thes