The first adiabatic ionization potential of Ar2

Abstract

The high resolution zero-kinetic-energy (ZEKE) photoelectron spectrum of Ar2 has been recorded between 116500 and 128500 cm-1. The spectrum consists of a progression of 52 vibrational bands in the A 2Σ1/2u+←X 1Σg+ (X 10g+ in Hund's case (c) notation) photoelectronic transition. The absolute numbering of the vibrational progression in the A←X transition is achieved by measuring the isotope shifts of two vibrational bands of the 36Ar2 molecule. From the analysis of the vibrational progression the first adiabatic ionization potential of Ar2 has been determined to be 116593.5±6.0 cm-1 (14.4558±0.0007 eV) from which a dissociation energy D0 of 10601.2±6.0 cm-1 (1.3144±0.0007 eV) results for the A 2Σ1/2u+ ground state of Ar2+. The potential curve of the ground ionic state in the vicinity of the potential minimum is adequately represented by a Morse potential with ωe+=307.0±0.4 cm-1 and ωexe+=2.05±0.05 cm-1. The position of higher members of the vibrational progression with υ+>25 cannot be fitted accurately with a Morse potential. © 1997 American Institute of Physics.