THE FIRST ADIABATIC IONIZATION-POTENTIAL OF AR-2

The high resolution zero-kinetic-energy (ZEKE) photoelectron spectrum of Ar-2 has been recorded between 116500 and 128500 cm(-1). The spectr um consists of a progression of 52 vibrational bands in the A (2) Sigm a(1/2u)(+) <-- X (1) Sigma(g)(+) (X O-1(g)+ in Hund's case (c) notatio n) photoelectronic transition. The absolute numbering of the vibration al progression in the A <-- X transition is achieved by measuring the isotope shifts of two vibrational bands of the Ar-36(2) molecule. From the analysis of the vibrational progression the first adiabatic ioniz ation potential of Ar-2 has been determined to be 116593.5 +/- 6.0 cm( -1) (14.4558 +/- 0.0007 eV) from which a dissociation energy D-0 of 10 601.2 +/- 6.0 cm(-1) (1.3144 +/- 0.0007 eV) results for the A (2) Sigm a(1/2u)(+) ground state of Ar-2(+). The potential curve of the ground ionic state in the vicinity of the potential minimum is adequately rep resented by a Morse potential with omega(e)(+) = 307.0 +/- 0.4 cm(-1) and omega(e)x(e)(+) = 2.05 +/- 0.05 cm(-1). The position of higher mem bers of the vibrational progression with v(+) > 25 cannot be fitted ac curately with a Morse potential. (C) 1997 American Institute of Physic s.