研究目的
To calculate and analyze the two- and three-photon partial photoionization cross sections of Li+, Ne8+, and Ar16+ ions under XUV radiation, using ab initio configuration interaction methods and lowest-order perturbation theory.
研究成果
The study successfully calculates two- and three-photon partial ionization cross sections for Li+, Ne8+, and Ar16+, revealing dominance of 1D channels in two-photon ionization and decreases in cross sections with increasing atomic number. Results align with scaling laws and prior theoretical works, providing valuable data for experiments with X-ray free-electron lasers. Future work could address resonant cases with density matrix methods and extend to higher Z ions or different polarizations.
研究不足
The use of LOPT is limited to non-resonant regions and specific intensity conditions; it fails near resonances where spontaneous decay widths are ignored, leading to unphysical singularities. The dipole approximation is assumed, which may not hold for very high Z ions beyond those studied. Computational constraints include basis set size and box radius choices, potentially affecting accuracy for highly excited states.
1：Experimental Design and Method Selection:
The study employs an ab initio configuration interaction (CI) method combined with lowest-order perturbation theory (LOPT) to calculate multiphoton ionization cross sections. The theoretical framework involves solving the Schr?dinger equation for one-electron and two-electron systems using B-spline basis sets for discretized energy spectra.
2：Sample Selection and Data Sources:
The samples are theoretical models of Li+, Ne8+, and Ar16+ ions, with atomic numbers Z=3, 10, and 18, respectively. Data sources include numerical solutions of quantum mechanical equations, with comparisons to NIST database values for validation.
3：List of Experimental Equipment and Materials:
No physical equipment is used; the study is computational, relying on theoretical models and numerical methods. Software or computational tools for B-spline expansions and matrix diagonalizations are implied but not specified.
4：Experimental Procedures and Operational Workflow:
The procedure involves: (a) Solving the one-electron Schr?dinger equation for hydrogenic ions (Li2+, Ne9+, Ar17+) using B-spline polynomials. (b) Constructing two-electron wavefunctions via configuration interaction for Li+, Ne8+, Ar16+. (c) Applying LOPT to compute two- and three-photon ionization cross sections, evaluating dipole matrix elements in length and velocity forms. (d) Analyzing cross sections for photon energy dependence and resonance features.
5：6+. (c) Applying LOPT to compute two- and three-photon ionization cross sections, evaluating dipole matrix elements in length and velocity forms. (d) Analyzing cross sections for photon energy dependence and resonance features.
Data Analysis Methods:
5. Data Analysis Methods: Data analysis includes comparing calculated energies with NIST standards, evaluating cross sections in SI units (cm^4 s for two-photon, cm^6 s^2 for three-photon), and assessing agreement between length and velocity forms of dipole operators. Statistical techniques are not explicitly mentioned; the focus is on numerical convergence and theoretical consistency.
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