Observation of an (N+ - N ≤ 4) ro-vibrational transition in the photoionization of D2

We present high-resolution photoelectron spectra (PES) of D2 in the photon energy range from 15.648 to 15.677 eV. This range encompasses autoionizing Rydberg states of D2 converging on various vibrational levels of the X 2Σg+ state of the D 2+ ion. The PES show features that correspond to the transitions, D2 X 1Σg (v ≤ 0, N ≤ 0) → D2+ X 2Σg + (v+ ≤ 0, N+ ≤ 0, 2, and 4). This is the first time that a change of ΔN ≤ N+ - N ≤ 4 in rotational angular momentum has been reported in a PES, where the magnetic field was negligible (less than a few milligauss). The autoionizing state giving rise to the ΔN ≤ 4 transition is observed at a photon energy of 15.674 eV and is assigned to the R(2) n ≤ 5pπ Rydberg state converging to the v + ≤ 4 vibrational level of the D2+ ion. It is suggested that the large change in rotational angular momentum results from the relatively long lifetime of this state. © 2006 IOP Publishing Ltd.