Pulsed-Field Ionization Zero-Kinetic-Energy Photoelectron Spectra of Ar(2)

The pulsed-field ionization (PFI) zero-kinetic-energy (ZEKE) photoelectron spectra of Ar(2) were measured between 117 000 cm(-1) (14.5 eV) and 128 300 cm(-1) (15.9 eV) using the penetrating field technique and synchrotron radiation at resolutions of up to 1 meV. The A(2)Sigma(+)(1/2u) ground state and B(2)Pi(1/2g) and C(2)Pi(3/2u) excited states were assigned to those spectra. The first adiabatic ionization potential of Ar(2) was determined to be 14.4572 +/- 0.0007 eV. A Le Roy-Bernstein plot and a Birge-Sponer plot were used to determine the dissociation limit of the A(2)Sigma(+)(1/2u) ground state. The vibrational level of the C(2)Pi(3/2u) excited state was observed for the first time. The effective lifetime for high-n Rydberg states converging on the vibrational levels of the C(2)Pi(1/2u) excited state is estimated to be shorter than those of the A(2)Sigma(+)(1/2u), B(2)Pi(1/2g), and C(2)Pi(3/2u) states, because the spectrum could not be observed on the PFI-ZEKE experiment. The threshold photoelectron-photoion coincidence spectra of Ar(2) were also measured and compared with the spectra obtained from the PFI-ZEKE experiment. Copyright 1999 Academic Press.