Multiphoton ionization of molecules under the conditions of strong field-induced perturbation of Rydberg states

摘要

Multiphonon ionization of the H_2 molecule under the action of a weak (probe) field, which provides the initial population of low-lying (working) level, and intense monochromatic linearly polarized radiation is studied. The multiphoton ionization process occurs under the conditions of strong field perturbation of two intermediate Rydberg series, np0(~1sum_(u~+)) and np~2(~1II_u), of the optical R(0) branch which have different ionization potentials. The series are occupied simultaneously as a result of single-photon absorption by an excited H_2 molecule in the working state 4s#sigma#H min ~1 sum_(g~+) (v = 0). As a result of the irregularity in the arrangement of the intermediated levels from a large group of states that are combined in the multiphoton ionization process a sharp and irregular change occurs in the dependence of the shifts and widths #GAMMA#_n of the levels on the intensity f of the strong field in a transition from one level to another. It is shown that for field intensities f such that the level widths remain much less than the splitting between the levels (#GAMMA#_n 1~3) the stabilizing effect (i.e., the field-inducted narrowing of the levels as f -> propor. to) in the form #GAMMA#_n propor. to 1/f~2 (as happens in atoms with a structureless core) is not observed in molecular systems.