Photoelectron spectra of N-2(+): Rotational line profiles studied with HeI-excited angle-resolved spectroscopy and with synchrotron radiation

We have recorded angle-resolved He I photoelectron spectra of the three out ermost valence states in Nz with high enough resolution to observe rotation al lime profiles. For the two Sigma states, the X (2)Sigma(g)(+) and the B (2)Sigma(u)(+), we found that the rotational branches corresponding to diff erent changes in rotational quantum number can differ dramatically in beta value. The well-known difference in beta value for the nu = 0 and nu = 1 vi brations of the X (2)Sigma(g)(+) State was found to be due to different rot ational branching ratios and also different beta values of the rotational b ranches. For the nu = 0 - 2 vibrations of the A (2)Pi(u) state, the beta va lue difference between rotational branches is much less pronounced than in the X and B states. We have also recorded synchrotron-radiation-excited pho toelectron spectra of the nu = 0 vibrational peaks of the X (2)Sigma(g)(+) and B (2)Sigma(u)(+) states where rotational line profiles are resolved. Th e intensities of the rotational branches were studied as function of photon energy, the X state between 23 and 65 eV, and the B state between 23 and 4 5 eV. The results for the X state have recently been presented in a Letter [G. Ohrwall, P. Baltzer, and J. Bozek, Phys. Rev. Lett. 81, 546, 1998]. The rotational branching ratios of the two states have very different behavior s as functions of photon energy. The relative intensities of the rotational branches in the X state change significantly over the studied energy range . The 3 sigma(g) --> k sigma(u) shape resonance apparently gives rise to a non-Franck-Condon-like behavior for the rotational branching ratio of the X state. In the B state, the rotational branching ratios remain essentially constant over the studied energy range. [S1050-2947(99)07903-2].