Towards resolving the hyperfine structure in ions by photoelectron spectroscopy

Pulsed held ionization experiments have been performed on high Rydberg stat es of the O-2 and the H2O molecules and of several isotopes of the krypton atom. Using a high resolution extreme ultraviolet (XUV) laser system pulsed held ionization zero kinetic energy (PFI-ZEKE) photoelectron spectra of th e O(2)(+)X(2)Pi(g,Omega)(upsilon(+) = 2) <-- O(2)X(3)Sigma(g)(-)(upsilon = 0) and the H2O+ (X) over tilde B-2(1) <-- H2O (X) over tilde (1)A(1) transi tions have been recorded at a resolution of 0.3 cm(-1). These spectra repre sent the first photoelectron spectra that provide information on the energy level structure of molecular ions that goes beyond that contained in the r otational structure, and provide new, fundamental information on molecular photoionization. The electron spin splittings in the ground neutral state o f O-2 have been fully resolved and the results are compared with nb initio predictions of the threshold photoelectron spectrum by Braunstein, M., McKo y, V., and Dixit, S. N. (1992, J. chem. Phys., 96, 5726). The spin-rotation splittings of the rotational levels of the H2O+ (X) over tilde B-2(1) Stat e also have been resolved, and the intensity distributions in the photoelec tron spectrum are influenced by the relative orientation of the electron sp in and rotational angular mometum vectors. Pulsed held ionization spectra o f high Rydberg states of the krypton atom have been measured at a resolutio n of 250 kHz, and the hyperfine structure in the spectrum of the Kr-83 isot ope has been resolved at n approximate to 50. From these measurements it is inferred that the measurement of hyperfine structure intervals in ions by photoelectron spectroscopy and pulsed held ionization techniques may become feasible in the near future.