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Wyszukujesz frazę "Koch, M." wg kryterium: Autor


Wyświetlanie 1-2 z 2
Tytuł:
Polarization Dependence of Microwave "ionization" of Excited Hydrogen Atoms
Autorzy:
Koch, P. M.
Powiązania:
https://bibliotekanauki.pl/articles/1968532.pdf
Data publikacji:
1998-01
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
32.80.Rm
05.45.+b
42.50.Hz
Opis:
After a brief review of the ionization of excited hydrogen atoms by a linearly polarized field, we discuss experimental results for the polarization dependence of this process. Experiments at ω/2π = 9.904 GHz used two different ranges of principal quantum number n$\text{}_{0}$ between 29 and 98. At low scaled frequencies, Ω ≲ 0.1, ionization data for certain narrow ranges of n$\text{}_{0}$ exhibit striking sensitivity to fields with elliptical polarization not too far from circular polarization. Classical calculations reproduce this behavior and show it to be the result of 2ω driving terms that appear when the Hamiltonian is transformed to a frame rotating at ω. It shows how higher-dimensional dynamics can influence the ionization and be used to control it when the polarization departs from linear or circular polarization. At higher scaled frequencies, 0.6 ≲ Ω$\text{}_{0}$ ≲ 1.4, near the onset of ionization circularly and elliptically polarized data show surprising similarities with linearly polarized data in a parameter regime where the ionization dynamics is dominated by the influence of the pendulumlike resonance zone centered at scaled frequency n$\text{}_{0}^{3}$ω ≡ Ω$\text{}_{0}$ = 1. The stabilizing influence of this zone can be understood classically, but nonclassical stability associated with quantal separatrix states at its edge is a semiclassical effect.
Źródło:
Acta Physica Polonica A; 1998, 93, 1; 105-133
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
The Kinetics of the Spin-Conversion of Positronium Measured by β$\text{}^{+}$γ∆E Age-Momentum Correlation
Autorzy:
Lauff, U.
Maier, K.
Major, J.
Seeger, A.
Stoll, H.
Wesołowski, P.
Koch, M.
Bilard, I.
Abbé, J.
Duplâtre, G.
Powiązania:
https://bibliotekanauki.pl/articles/1929104.pdf
Data publikacji:
1993-03
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
Opis:
Age-momentum correlation (AMOC) measurements provide time-resolved information on the momentum distribution of annihilating electron-positron pairs through correlated determination of Doppler broadening (∆E) of the 511 keV annihilation radiation line and positron age. In the β$\text{}^{+}$γ∆E AMOC technique implemented at the Stuttgart pelletron accelerator the start signals for the age measurements are generated when the relativistic positrons pass through a fast plastic scintillator, which has a detection efficiency close to unity. Beam-based β$\text{}^{+}$γ∆E AMOC measurements thus combine high β$\text{}^{+}$γ∆E triple-coincidence rates with low background. From a practical point of view this constitutes a major progress compared to conventional (source-based) γγ∆E AMOC measurements. The AMOC technique permits direct access to a wide variety of time-dependent processes, among them the reaction kinetics in positronium chemistry. As an example, we present a β$\text{}^{+}$γ∆E AMOC investigation of the kinetics of a spin-conversion reaction of positronium in methanol induced by the presence of a nitrosyl free-radical paramagnetic solute (4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl , HTEMPO). The AMOC measurements allowed the time-resolved observation of the spin-conversion process, which had been investigated before by uncorrelated positron lifetime and Doppler-broadening measurements. It is found that within the concentration range investigated (≤ 0.1 mol/l) the spin-conversion reaction rate at room temperature depends linearly on the HTEMPO concentration with a reaction-rate constant k$\text{}_{conv}$ = (22.5 ± 0.5) × 10$\text{}^{9}$ l mol$\text{}^{-1}$ s$\text{}^{-1}$.
Źródło:
Acta Physica Polonica A; 1993, 83, 3; 349-358
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
    Wyświetlanie 1-2 z 2

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