No abstract

Photoionization from H@C60 and Ar@C60 is studied by employing two different model potentials to simulate the endohedral environment. The contrast between the diffusive Gaussian annular square well (GASW) and the compact annular square well (ASW) model potential on the photoionization dynamics is explored by studying the cross-section, phase shift, and Wigner time delay. A realistic description of the fullerene environment requires the right amount of diffuseness and compactness, and the proposed GASW model has both of these attributes. The dynamical properties of an encapsulated atom are studied systematically as a function of the well depth, and it is found that the GASW model induces mild and realistic confinement oscillations on the photoionization parameters in comparison with the ASW case. In addition, the present work brings out a few other interesting features. For a confining well depth of 1.03 a.u., the phase of the dipole matrix elements takes sharp jumps akin to the behavior of dipole phases at the Cooper minimum. In the case of free Ar, the correlation effects contribute less to the time delay in comparison with screening effects near the Cooper minimum. In search of a realistic potential to mimic confinement, the GASW model potential is recommended.

Time delay of photoemission from valence ns, np 3/2 , and np 1/2 subshells of noble-gas atoms is theoretically scrutinized within the framework of the dipole relativistic random phase approximation. The focus is on the variation of time delay in the vicinity of the Cooper minima in photoionization of the outer subshells of neon, argon, krypton, and xenon, where the corresponding dipole matrix element changes its sign while passing through a node. It is revealed that the presence of the Cooper minimum in one photoionization channel has a strong effect on time delay in other channels. This is shown to be due to interchannel coupling.

The complex Kohn and polyatomic Schwinger variational techniques have been employed to illustrate the interchannel coupling correlation effects in the valence photoionization dynamics of SF6. Partial photoionization cross sections and asymmetry parameters of six valence subshells (1t1g, 5t1u, 1t2u, 3eg, 1t2g, 4t1u) are discussed in the framework of several theoretical and experimental studies. The complex Kohn results are in rather good agreement with experimental results, indicative of the fact that the interchannel coupling effects alter the photoionization dynamics significantly. We find that the dominant effect of interchannel coupling is to reduce the magnitude of shape resonant cross sections near the threshold and to induce resonant features in other channels to which resonances are coupled. The long-standing issue concerning ordering of the valence orbitals is addressed and confirmed 4t1u (6)1t2g (6)3eg (4)(5t1u (6)+1t2u (6)) 1t1g (6) as the most likely ordering.

Avoided crossing is one of the unique spectroscopic features of a confined atomic system. Shannon information entropy of the ground state and some of the excited states of confined H atom as a predictor of avoided crossing is studied in this work. This is accomplished by varying the strength of the confinement and examining structure properties like ionization energy and Shannon information entropy. Along with the energy level repulsion at the avoided crossing, Shannon information entropy is also exchanged between the involved states. This work also addresses a question: In addition to that regarding localization, what other property of the system can be extracted from Shannon entropy? Insightful connection is discovered between Shannon entropy and the average value of confinement potential, Coulomb potential, and kinetic energy.