The influence of a parallel magnetic field on the ionization of a hydrogen atom in an electric field

The ionization of a hydrogen atom in an electric field plus a variable magnetic field has been examined. The dynamic motion of the electron is generated by exciting the hydrogen atom from its ground state using a short laser pulse. The results show that the atom ionizes by emitting a train of electron pulses. As the magnetic field is very weak, the ionization process of the hydrogen atom is nearly the same as the case of hydrogen atom in an electric field. With the increase of the magnetic field, a series of electron pulses appear in the ionization process. Not only the trajectories launched with large angles can pass through the saddle point and escape, but also those orbits with small initial outgoing angles can escape. The escape-time plot and the ionization rate curve become much more complicated. This is caused by classical chaos, which occurs for strong magnetic fields. Our theoretical analysis will be useful for guiding experimental studies of the ionization of atoms in the external fields, under chaotic conditions.