Observation of an (N+-N=4) ro-vibrational transition in the photoionization of D-2

We present high-resolution photoelectron spectra (PES) of D-2 in the photon energy range from 15.648 to 15.677 eV. This range encompasses autoionizing Rydberg states of D-2 converging on various vibrational levels of the X-2 Sigma(+)(g) state of the D-2(+) ion. The PES show features that correspond to the transitions, D2X1 Sigma(g)(v = 0, N = 0) -> (D2+X2)Sigma(+)(g)(v(+) = 0, N+ = 0, 2, and 4). This is the first time that a change of Delta N = 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 Delta N = 4 transition is observed at a photon energy of 15.674 eV and is assigned to the R(2) n = 5p pi Rydberg state converging to the v(+) = 4 vibrational level of the D-2(+) ion. It is suggested that the large change in rotational angular momentum results from the relatively long lifetime of this state.