Rotationally resolved pulsed field ionization photoelectron bands for O-2(+)(a (4)Pi(u), v(+)=0-18) in the energy range of 16.0-18.0 eV

We have obtained rotationally resolved pulsed field ionization-photoelectro n (PFI-PE) spectra of O-2 in the energy range of 16.0-18.0 eV, covering ion ization transitions O-2(+)(a (4)Pi(u), v(+)=0-18,J(+))<-- O-2(X (3)Sigma(g) (.), v "=0,N "). Although these vibrational PFI-PE bands for O-2(+)(a (4)Pi (u), v(+)) have significant overlaps with those for O-2(+)(X (2)Pi(g)) and O-2(+)(A (2)Pi(u)), we have identified all O-2(+)(a (4)Pi(u), v(+)=0-18) ba nds by simulation of spectra obtained using supersonically cooled O-2 sampl es with rotational temperatures approximate to 20 and 220 K. While the v(+) =4-18PFI-PE bands represent the first rotationally resolved photoelectron d ata for O-2(+)(a (4)Pi(u)), the PFI-PE bands for O-2(+)(a (4)Pi(u), v(+)=10 -18) are the first rotationally resolved spectroscopic data for these level s. The simulation also allows the determination of accurate ionization ener gies, vibrational constants, and rotational constants for O-2(+)(a (2)Pi(u) , v(+)=0-18). The observed intensities of spin-orbit components for the maj ority of O-2(+)(a (2)Pi(u), v(+)) vibrational bands are in accordance with the forced spin-orbit/rotational autoionization mechanism. (C) 2000 America n Institute of Physics. [S0021-9606(00)02003-1].