EVIDENCE FOR SPIN-ORBIT AUTOIONIZATION IN THE ZERO KINETIC-ENERGY PHOTOELECTRON-SPECTRUM OF MOLECULAR-IODINE IONIZED VIA THE VALENCE B-3-PI(0+U) STATE

The two-color (1+2') zero kinetic energy pulsed field ionization (ZEKE -PFI) spectrum of I-2 ionized via the valence B-3 Pi(0u+), state has b een recorded for the first time. Ionization into both X(2) Pi(3/2,g) a nd X(2) Pi(1/2,g) spin-orbit ionic substates was achieved following ex citation of the predominantly [(2) Pi(1/2)] core character valence B s tate. Both spin-orbit state spectra exhibit greatly extended vibration al progressions with the lower spin-orbit state vibrational progressio n extending well beyond the onset of the X(2) Pi(1/2g) state to at lea st v(+) = 62 while the X(3) Pi(1/2,g) state progression can be followe d as far as v(+) = 34. Although the extent of the vibrational progress ions can be adequately simulated through the calculation of Franck-Con don factors, in practice the distribution of peak intensities and obse rved spin-orbit branching ratio reflects the considerable contribution of both spin-orbit and field-induced resonant autoionization processe s. Accidental resonances at the two-photon level with ion-pair states further perturb the distribution of peak intensities. The adiabatic io nization energies of 75 069 +/- 2 cm(-1) for the X(2) Pi(3/2,g) state and 80 266 +/- 2 cm(-1) for the X(2) Pi(1/2,g) state are in exact agre ement with the values determined in an earlier report of the (2+1') ZE KE-PFI spectrum of iodine.