High-np Rydberg states of atomic carbon studied through vuv and uv double resonance

We report on the use of an efficient stepwise-resonant two-photon excitation scheme to study high principal quantum number even-parity (2pnp) Rydberg states of atomic carbon. This scheme uses intense vacuum ultraviolet light to drive the resonance transition of the atoms, followed by excitation to Rydberg states with tunable ultraviolet light. Atomic carbon was produced under high vacuum conditions using laser ablation. Analysis of the spectrum of the unperturbed J53 Rydberg series below and above the first ionization limit yielded a new value for the ionization potential of the atom, with an accuracy primarily limited by the accuracy with which the intermediate state energy is known. The spectra of the J50, 1, and 2 Rydberg states all displayed the effects of coupling between different series converging to the two fine-structure states of the ion core. These spectra have been successfully reproduced using ab initio R-matrix calculations. @S1050-2947~98!09011-8#