Rydberg state decay in inhomogeneous electric fields

An extension of the model of Merkt and Zare [J. Chem. Phys. 101, 3495 (1994 )] is presented to describe the effects of static inhomogeneous electric fi elds, which arise experimentally from combinations of applied (or stray) ho mogeneous fields and the presence of charged particles, on Rydberg states o f atoms and molecules. The effect of an arbitrary number of charged particl es is included and the effects of nonzero quantum defects are investigated. A quantization axis rotation procedure is defined, allowing clear distinct ion between homogeneous and inhomogeneous field effects. Calculations are r eported of the time-dependent decay of a coherent population of eigenstates for n=20, 33, and 50, involving diagonalization of the full n(2)xn(2) matr ix. Calculations are also carried out for n=100 by pre-diagonalization of t he full homogeneous field perturbation followed by a restricted basis set d iagonalization for the inhomogeneous part of the perturbation. The inclusio n of nonzero quantum defects has a substantial impact on the m(l) mixing, c onfining significant mixing to a narrow range of radial and angular positio ns of the ion. An applied homogeneous field of order the Inglis-Teller fiel d is required in combination with the field due to the ions. The dynamics a re very different according to whether np or nf series carry the transition probability. For np-state population, the maximum stabilization is achieve d at ion-Rydberg distances of around 5n(2)a(0), with the ion almost perpend icular to the applied homogeneous field. For an initial nf population the i on perturbation may have a destabilizing effect at sufficiently small homog eneous field (less than or equal to 0.1F(IT)). Significant effects of laser polarization on the stability are reported. Calculations for a realistic p seudo-random distribution of ions and Rydbergs suggest that m(l) mixing by ions will never reach the complete mixing limit, but that at least an order of magnitude stabilization is achievable under a restricted range of condi tions. (C) 2000 American Institute of Physics. [S0021-9606(00)00118-5].