Application Of B-spline Basis Set Methods For The Spectral Calculation Of Atoms In Strong External Fields

Rydberg atoms are ideal systems for studying the effect of external fields on atoms due to its long lifetime and sensitivity to external fields. Atoms in external fields relate to many basic theoretical problems in atomic physics, e.g. the solution for non-separable system, the coupling of discrete and continuum states and its influence on the structure of the spectrum, the quantum-classical correspondence and so on. The research on atoms in strong fields can provide essential data for astrophysics, plasma physics, and other applications.In this paper, new effective methods dealing with the atoms in strong fields have been developed. These methods are applied to systematically investigate the spectra and resonances of alkali atoms in external electric and magnetic fields. The major contents of this paper are as follows:1. We calculated near-threshold diamagnetic spectra of Li and Na atoms in strong fields by B-spline basis plus model potential (B-spline+MP) approach. The angular wave-functions are expanded in terms of the symmetry-adapted B-spline functions. For Li atom, in contrast with R-matrix+MQDT, the B-spline+MP method obtains a higher spectral accuracy with a smaller computational effort over the energy range of our study. For Na atom, the contribution of continuum states to the spectra becomes significant near threshold region.2. We presented oscillator strength spectra of Li and Na in parallel electric and magnetic fields via the B-spline+MP method. In the case of Li atom, the oscillator strength is calculated and analysed in B = 0.594 T, F = 5.33 V/cm. We got the same form of spectrum byπphoto absorption from the Li (2s) initial state as that from the 3s state. The two spectra only differ by an overall constant. The structure of the spectrum, over the narrow energy ranges considered in this paper, can be independent of the initial state chosen for a given atom. The structure of the spectrum is determined by the final state only. Comparing the spectra of Li and Na, the marked effect of atomic core on the spectra can be found.3. We presented oscillator strength spectra of the hydrogen Balmer α series in strong magnetic and electric fields with arbitrary mutual orientation via the B-spline basis method. The results are in good agreement with the ones in literatures. It shows that the B-spline basis method can effectively deal with the problem of atoms in crossed fields.4. The B-spline-based coordinate rotation method plus model potential approach is applied for the first time to investigate the complex energies of low-lying Stark resonances of the lithium atoms. We further discuss and clarify the argument on energy positions and widths of resonance states in recent literatures. The calculated results show that this method has the advantages of simplicity, flexibility and small computational effort. The method can be extended easily to deal with the problem of alkali atoms in crossed fields.