High-resolution photoelectron spectroscopic study of the first electronic states of Kr-2(+)

The pulsed-field-ionization zero-kinetic-energy (PFI-ZEKE) photoelectron sp ectrum of Kr-2 has been recorded between 103 500 cm(-1) and 118 000 cm(-1). Photoelectronic transitions to four [the I(1/2u), I(3/2u), II(1/2u), and I I(1/2g) states] of the first six electronic states of Kr-2(+) have been obs erved. The photoelectronic transition to the ground I(1/2u) state consists of a long progression of vibrational bands, starting at v(+)=0. From the re solved isotopic substructure of vibrational levels with v(+)greater than or equal to 15, the absolute numbering of the vibrational quantum number coul d be determined. The analysis of the spectrum has led to improved values of the adiabatic ionization potential [IP(I(1/2u))=(103 773.6 +/-2.0) cm(-1)] , the dissociation energy [D-0(+)(I(1/2u))=(9267.8 +/-2.8) cm(-1)] and to t he determination of an analytical potential energy curve that reproduces th e experimental data from v(+)=0 to beyond 81% of the dissociation energy. T he transitions to vibrational levels of the I(1/2u) state with v(+)less tha n or equal to 30 and v(+)greater than or equal to 65 have vanishing Franck- Condon factors for direct ionization from the ground neutral state and gain intensity from transitions to low Rydberg states that belong to series con verging on excited electronic states of Kr-2(+). In the region immediately below the first dissociation limit of Kr-2(+), a second progression was obs erved and assigned to a photoelectronic transition to the I(3/2u) state. Th e adiabatic ionization potential [IP(I(3/2u))=(112 672.4 +/-2.0) cm(-1)], t he dissociation energy [D-0(+)(I(3/2u))=(369.1 +/-2.8) cm(-1)] and vibratio nal constants could be extracted for this state. Two further progressions w ere observed below the second dissociation limit of Kr-2(+) and assigned to transitions to the II(1/2u) and II(1/2g) states. The adiabatic ionization potentials [IP(II(1/2u))=(117 339.7 +/-2.0) cm(-1), IP(II(1/2g))=(117 802.6 +/-2.0) cm(-1)] and the dissociation energies [D-0(+)(II(1/2u))=(1071.7 +/ -2.8) cm(-1), D-0(+)(II(1/2g))=(608.8 +/-2.8) cm(-1)] were determined for t hese two ionic states. In the region just below the ionic dissociation limi ts, artifact lines are observed in the PFI-ZEKE photoelectron spectra at th e position of transitions to Rydberg states of the krypton monomer. At the lowest threshold, collisional and associative ionization of the long lived atomic Rydberg states leads to the formation of ZEKE electrons; at the uppe r threshold, the rapid autoionization of the atomic Rydberg states forms hi gh ion concentrations, and the electrons that remain trapped in the ion clo ud are released by the delayed pulsed field used to produce and extract the PFI-ZEKE electrons. (C) 2001 American Institute of Physics.