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

The pulsed-field ionization (PFI) zero-kinetic-energy (ZEKE) photoelectron spectra of Ar₂ 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 A²Σ⁺_1/2u ground state and B²Π_1/2g and C²Π_3/2u excited states were assigned to those spectra. The first adiabatic ionization potential of Ar₂ 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 A²Σ⁺_1/2u ground state. The vibrational level of the C²Π_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 C²Π_1/2u excited state is estimated to be shorter than those of the A²Σ⁺_1/2u, B²Π_1/2g, and C²Π_3/2u states, because the spectrum could not be observed on the PFI-ZEKE experiment. The threshold photoelectron-photoion coincidence spectra of Ar₂ were also measured and compared with the spectra obtained from the PFI-ZEKE experiment.