A Studying Of Recurrence Spectra Of Helium Rydberg Atoms In External Fields

The photo-absorption phenomenon of highly excited Rydberg atoms in strong external fields has attracted much attention in recent years, which is a typical example for understanding the conception of quantum chaos. The semiclassical closed-orbit theory has been extensively used to explain this phenomenon due to its clear physical picture and wide availability, and has become a link between quantum and classical theory. This theory has successfully calculated and interpreted the photo-absorption spectra of H- in various external fields and has been applied to describe the photo-excitation, wave packet dynamics of some atoms and molecules such as H, Li and so on.To multielectron atoms, the theoretical treatment is more difficult than hydrogen atoms. The helium atoms are the prototypical quantum atomic system whose underlying classical dynamics is chaotic, induced by core scattering. Previously theoretical and experimental studies about the multielectron atoms have found that the effects of the non-hydrogenic ionic core should be considered. It is core scattering that leads to new recurrence peaks called combination recurrence. Because two electrons of the He atom have significant correlation, the exchange potential must be considered. At some value of scaled energy, the returning waves would become infinite as a focus or caustic passed through the origin. So it is necessary to correct and extend the primitive closed-orbit theory.In this paper, we put forward a new model potential based on the quantum defect theory, which includes not only the core attractive potential, but also the exchange potential between the excited electron and another electron. We calculate the closed orbits and the recurrence spectra with finite resolution using special region-splitting consistent and iterative method, i.e., the spectral structure is measured in larger energy scale. In other words, there are only the contributions of closed orbits with smaller actions, which are the most decisive for the spectral behavior, have been involved. In numerical implementation of the calculating theprocess of the orbit returning and core scattering should be repeated and iterative, so as to get a convergent results. It is done we obtained the recurrence spectra of triplet helium atoms in parallel electric and magnetic fields at scaled energy ε =0.03, n≈40, m=0. In order to compare with resent of the experimental observation, we have also displayed the recurrence spectra of helium atoms with the same exchange potential but in single electric field at scaled energy ε =-2.7 case, and shown that our approach is in better agreement with the experimental data than that previous theoretical calculations. The results also imply that the core-scattering effects are important and our model potential is correct. Therefore, it is necessary to consider the electrons exchange effect for studying the absorption spectra of multielectronic atoms in strong external fields. The amplitudes of some peaks are overevaluated due to not inserting the uniform approximations, when we used the uniform approximates method to correct the recurrence spectra of helium atoms, the high of the peaks should be reduced, and our result would be in good agreement with the experimental data.For the recurrence spectra of helium atoms in perpendicular electric and magnetic fields, because of the simultaneous action and competitions of the electric field, the magnetic field and the nuclear coulomb potential, the region of regular motion reduces farther more, the closed orbits extend to three degrees of freedom, we calculate the recurrence spectra of Heatom in perpendicular magnetic and electric field at ε= -0.03, n≈40, F = 0.01,m = 0. We have also compared the results with that of hydrogen atom .Our calculations certify the validity of the closed orbits theory and make some improvement upon it, and imply that the core-scattering effects is important.In the case of He Rydberg atom, our works are not only the extension but also the validation and supplement for the closed-orbit theory. So fa...