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Measurement of photoionization cross-section of Li (2p, 3d) excited states using thermionic diode detector
摘要： Studies on photoionization cross-section measurement of lithium 2p and 3d excited states selectively populated by single and two photons are reported. The photoionization is carried out in a heat-pipe cum thermionic diode detector using nitrogen laser pumped pulsed dye laser. Rhodamine perchlorate (Rh-640) dye is used to generate the desired tunable laser output in the range of 635 to 675 nm. Both, the thermionic diode detector and dye laser are developed in-house. A negative space charge region formed around diode cathode filament is illuminated by dye laser exciting pulse followed by ionizing UV radiation from nitrogen laser. The effect of ionizing laser pulse energy and precise tuning of dye laser on photoionization signal, across 670.780 nm (2S1/2 → 2P1/2,3/2) single-photon transition and 639.145 nm (2S1/2 → 2D3/2,5/2) two-photon transition are studied. The results obtained are compared with model calculations of photoionization signal saturation curve. The ionization cross-section for both the states (2P1/2, 2D5/2) are determined as 15.40 ± 2.8 Mb and 8.04 ± 1.6 Mb, respectively and atomic number density N ～ 5.6 × 10^8 (cm^?3).
关键词： Dye laser,Photoionization cross-section,Thermionic diode,Heat-pipe,Lithium
更新于2025-09-19 17:15:36
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Binding energies and photoionization cross-sections of donor impurities in GaN/AlxGa1a??xN spherical quantum dot under hydrostatic pressure
摘要： In this paper, the binding energy and photoionization cross-section of donor impurity state in GaN/AlxGa1?xN quantum dot structure are studied theoretically by using variational method. The variation of binding energy and photoionization cross-section with core and shell sizes at di?erent impurity locations under hydrostatic pressure is calculated numerically. The results show that the binding energy decreases monotonously with the core size at di?erent impurity locations for GaN/AlxGa1?xN core/shell quantum dot. In contrast, for the inverted core/shell quantum dot, the binding energy exhibits di?erent trends with the increase of core size at di?erent impurity locations. But the binding energy decreases monotonically with the shell size for both of them. Moreover, when the photon energy is approximately equal to the donor binding energy, the peak of the photoionization cross-section appears. There will be di?erent peak shifts under di?erent conditions, and its peak intensity increases with the increase of core and shell sizes. When the hydrostatic pressure is applied, the binding energy and the peak strength of the photoionization cross-section increase with the increase of the pressure.
关键词： hydrostatic pressure,Spherical quantum dot,binding energy,photoionization cross-section
更新于2025-09-19 17:13:59
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Lanczos-based equation-of-motion coupled-cluster singles-and-doubles approach to the total photoionization cross section of valence excited states
摘要： Excitation energies and oscillator strengths of the first two electronically excited states of helium, water, sulfur dioxide, molecular nitrogen, and carbon monoxide were obtained from an asymmetric-Lanczos-based formulation of the equation-of-motion coupled cluster singles and doubles approach. The total photoionization cross sections were generated by two different methodologies: an analytic continuation procedure based on the Padé approximants and the Stieltjes imaging technique. The results are compared with theoretical photoionization cross sections from algebraic diagrammatic construction [ADC(2)] and ADC(2)-x calculations [M. Ruberti et al., J. Chem. Phys. 140, 184107 (2014)] and with available experimental data.
关键词： Stieltjes imaging technique,coupled-cluster singles-and-doubles,photoionization cross section,Lanczos-based equation-of-motion,valence excited states,Padé approximants
更新于2025-09-12 10:27:22
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Partial Photoionization Cross Section of Collinear eZe Helium: Numerical Confirmation of Semiclassical Predictions
摘要： Based on the semiclassical theory of chaotic scattering, Tanner et al. [J. Phys. B 40, F157 (2007)] proposed the fluctuation in the partial photoionization cross section of helium below the double-ionization threshold would show the same characteristics as in the total cross section, predicting that the Fourier spectrum of the fluctuation reveals peaks at the classical actions of closed triple collision orbits and the amplitude of the fluctuation decreases algebraically as the energy approaches the double-ionization threshold. In that paper, however, the predictions were not clearly confirmed due to the lack of experimental data with sufficient accuracy. So instead, we calculate the partial photoionization cross sections of collinear eZe helium for the energy range from the single-ionization threshold I20 to I32 in order to numerically confirm the predictions. Analysis of the fluctuation in the partial cross section shows that the predictions are indeed valid. Our findings mean that the fluctuation in the partial photoionization cross section can be described by classical triple collision orbits in the semiclassical limit. Thus it explains in a natural way the mirroring and mimicking structures observed in cross section signals for different ionization channels.
关键词： Partial photoionization cross section,Collinear eZe helium,CTCO,Scaling law
更新于2025-09-10 09:29:36
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Vibronic structure and photoelectron angular distribution in the photoelectron spectrum of ICN
摘要： The valence shell photoelectron spectrum of ICN has been simulated using the equation-of-motion coupled-cluster method to calculate the ionization energies and the norms of the Dyson orbitals to describe the intensity of the photoelectron bands. The simulated spectrum not only reproduces the position and intensity of the four main bands observed in the experimental photoelectron spectrum, but the vibronic structure present in the individual photoelectron bands is also reproduced to a reasonable extent. The agreement between the experimental and simulated vibronic structures at higher energies corresponding to the ?A and ?B states is particularly noteworthy. Additionally, the photoionization cross section and asymmetry parameter have been calculated for the ionization of four outermost valence molecular orbitals in the photon energy range of 0–50 eV. The computed asymmetry parameters are found to provide a qualitative description of the corresponding experimental measurements. The shape-resonance seen in the experimental asymmetry parameters and the trends seen in the calculated cross section for the four ionization channels have been explained by the partial wave analysis of the contribution of the individual angular momentum channels to the photoelectron.
关键词： ICN,photoelectron spectrum,vibronic structure,equation-of-motion coupled-cluster method,Dyson orbitals,asymmetry parameter,photoionization cross section
更新于2025-09-10 09:29:36