Rotational autoionization of n p Rydberg series of D2

Two-color resonantly enhanced multiphoton ionization combined with photoelectron spectroscopy was used to study rotational autoionization of np Rydberg states of D2 near the first ionization threshold. This work represents an extension of the study by O’Halloran et al. [J. Chem. Phys. 90, 930 (1989)] on the analogous states of H2. As in that work, one laser was used to excite a two-photon transition to the E,F 1Σ+g, v′=E0, J′=0–4 levels, and a second laser was used to probe single-photon transitions to the rotationally autoionized np Rydberg states converging to the X 2Σ+g, v+=0, N̄+=1–6 rotational levels of D+2. Of the five dipole-allowed Rydberg series converging to v+=0 excited from each intermediate J′ level (J′≥2), two are allowed to rotationally autoionize in a coupling scheme that assumes ejection of pure p waves in the ionization process and singlet coupling of the spins of the ion core and the outgoing electron; members of these Rydberg series have large half-widths. As in H2, autoionization requiring the change of four quanta of rotational energy was found to be significantly slower than that requiring the minimum change of two quanta. Ionization was also observed for the series that are forbidden to rotationally autoionize according to this simple coupling scheme, and it is shown that both the inclusion of f waves in the autoionization process and singlet–triplet mixing may be required to explain these observations. By extending the wavelength region of the J′=4 spectrum beyond that of the earlier study on H2, rotational autoionization requiring even higher partial waves was observed.