No abstract

The 2p 5 1/2 np J = 0, 1, 2 and 2p 5 1/2 nf J = 2 autoionizing Rydberg states (ARS) of Ne have been studied by two-step two-colour photoionization of ground-state neon atoms via the intermediate states 2p 5 3/2 3s J = 1 and 2p 5 1/2 3s J = 1, followed by time-of-flight ion detection. Strong interference between the direct and virtual intershell photoexcitation channels in ARS production, especially for the np J = 0 series, is revealed. The computed reduced width r = 6431 cm −1 and the quantum defect µ p = 0.7634 of the 2p 5 1/2 13p J = 0 resonance agree well with the experimental results = 5334 cm −1 and µ p = 0.7662 determined with a Fano-type lineshape analysis. The measured lineshapes of the np J = 0, 1, 2 resonances are also in good agreement with the many-electron computation.

The pulsed-field-ionization zero-kinetic-energy photoelectron spectrum of Xe2 has been measured between 97 350 and 108200cm−1, following resonant two-photon excitation via selected vibrational levels of the C0u+ Rydberg state of Xe2. Transitions to three of the six low-lying electronic states of Xe2+ could be observed. Whereas extensive vibrational progressions were observed for the transitions to the I(3∕2g) and I(3∕2u) states, only the lowest vibrational levels of the II(1∕2u) state could be detected. Assignments of the vibrational quantum numbers were derived from the analysis of the isotopic shifts and from the modeling of the potential energy curves. Adiabatic ionization energies, dissociation energies, and vibrational constants are reported for the I(3∕2g) and the I(3∕2u) states. Multireference configurational interaction and complete active space self-consistent field calculations have been performed to investigate the dependence of the spin-orbit coupling constant on the internuclear distance. The energies of vibrational levels, measured presently and in a previous investigation (Rupper et al., J. Chem. Phys. 121, 8279 (2004)), were used to determine the potential energy functions of the six low-lying electronic states of Xe2+ using a global model that includes the long-range interaction and treats, for the first time, the spin-orbit interaction as dependent on the internuclear separation.

Photoionization and pulsed-field-ionization zero-kinetic-energy (PFI-ZEKE) photoelectron spectra of ArXe have been recorded between 96 400 and 108 200 cm(-1) following resonance-enhanced two-photon excitation via selected vibrational levels of the C 1 and D 0+ Rydberg states. The PFI-ZEKE photoelectron spectra consist of three vibrational progressions corresponding to the X 1/2<--X 0+, A1 3/2<--X 0+, and A2 1/2<--X 0+ transitions. From these progressions, adiabatic ionization energies, equilibrium internuclear distances, and vibrational constants have been derived for the lowest three electronic states of ArXe+. The photoionization spectra reveal long progressions of autoionizing Rydberg states converging to the lowest vibrational levels of the A1 3/2 state. A potential model has been developed that enables a global description of the low-lying electronic states of the heteronuclear rare gas dimer ions. The model explicitly treats the effects of the spin-orbit, charge-exchange, and long-range interactions. This model was used to obtain potential energy functions for all six low-lying electronic states of ArXe+ from the experimental positions of the vibrational levels of the X 1/2, A1 3/2, and A2 1/2 states relative to the ground neutral state and existing spectroscopic data on the B 1/2, C1 3/2, and C2 1/2 states.

The pulsed-field-ionization zero-kinetic-energy photoelectron spectrum of Xe(2) has been measured between 90 000 and 109 000 cm(-1) following single-photon excitation from the ground neutral state. Transitions to five of the six low-lying electronic states of Xe(2) (+) could be observed. Whereas extensive vibrational progressions were observed for the X0(g) (+)-->I(1/2u), I(3/2g), and II(1/2u) photoelectron transitions, only the lowest vibrational levels of the I(3/2u) and II(1/2g) states could be detected. Unambiguous assignments of the vibrational quantum numbers were derived from the analysis of the isotopic shifts of the vibrational bands and of the intensity distribution and from the modeling of the potential energy curves. Analytical potential energy curves of spectroscopic accuracy (i.e., approximately 1 meV) were determined for all six low-lying electronic states using a global model, which includes the first (charge-induced dipole, proportional to 1/R(4)) member of the long-range interaction series and treats the spin-orbit interaction explicitly. The assumption of an R-independent spin-orbit coupling constant was tested and found to be an excellent approximation.