Thomas J. Morgan

Closed-orbit recurrences in molecular hydrogen

Using scaled-energy Stark spectroscopy, we report the observation of recurrences due to closed orbits, both geometric and diffractive, in the {nu}=0, R=1, nd Rydberg series of H{sub 2} (16<n<26) interacting with the {nu}=0, R=3 series (13<n<15). The data support the molecular closed-orbit theory prediction of diffractive trajectories due to inelastic scattering of the excited electron on the molecular core. We have made similar measurements in He, and a comparison between the recurrence properties of H{sub 2} and its united atom equivalent is given.

Multielectron structure and dynamics in scaled-energy Stark photoabsorption and recurrence spectra

We use the 4s[3/2]{sub 2}{sup o} metastable state of atomic argon created by charge-transfer collisions between a 5 keV Ar{sup +} beam and K vapor to perform laser scaled-energy Stark photoabsorption and recurrence spectroscopy of even-parity Rydberg states, detected by field ionization and forced autoionization, in a region of the spectrum that contains two distinct perturbations. We apply a uniform electric field that changes with the frequency of the laser to maintain a constant scaled energy relative to the first ionization limit of the atom, associated with the ion core in a {sup 2}P{sub 3/2} configuration. Local perturbations to the Rydberg series (15{<=}n{<=}28) occur due to n{sup }=8 and 10 Stark states that belong to the series converging to the second ionization threshold with the ion core in a {sup 2}P{sub 1/2} configuration. The resulting absorption spectra show multielectron effects due to configuration interaction and angular momentum coupling. These effects have dynamical implications in the recurrence spectrum. In particular, the variations in the Stark structure of the absorption spectrum result in a recurrence spectrum that shows two prominent multielectron features. One is the presence of recurrence peaks with scaled actions less than that of the hydrogenic primitive orbit. We attributemorexa0» this to excitation in which both the ion core and the Rydberg electron absorb energy during photoexcitation. The second multielectron effect observed is recurrence peaks that occur at the sum of scaled actions of the primitive orbit (and its repetitions) associated with the pair of perturbations and a hydrogenic closed classical orbit. We attribute these peaks to core-changing inelastic scattering of the Rydberg electron with the ionic core due to angular momentum coupling. For comparison, we measured the regular autoionizing Rydberg series of argon between the first and second ionization thresholds, where no perturbing resonances exist.«xa0less