The first electronic states of Ar-2(+) studies by high resolution photoelectron spectroscopy

The pulsed-field-ionization (PFI) zero-kinetic-energy (ZEKE) photoelectron spectrum of Art has been recorded between 116500 cm(-1) and 128200 cm(-1). The spectrum consists of a long progression of transitions to the vibration al levels of the ground A (2)Sigma(1/2u)(+), State of Ar-2(+) with v(+) up to 52, a shorter progression of four bands attributed to transitions to the first. four vibrational levels of the C (2)Pi(1/2u) state and of a single sharp line assigned to the C (2)Pi(3/2u)(v(+) = 0) <-- X (1)0(g)(+)(v = 0) transition. Rotational constants of several vibrational levels of the A (2) Sigma(1/2u)(+) state have been determined from high resolution PFI-ZEKE pho toelectron spectra. From these measurements new information on the first el ectronic states of Ar-2(+) has been extracted. An analytical potential ener gy function has been derived for the A (2)Sigma(1/2u)(+) state which extend s to large internuclear distances (beyond 5 Angstrom) and reproduces all me asured vibrational energy levels up to v(+) = 52. The adiabatic ionization potential for the photoelectronic transitions to the A (2)Sigma(1/2u)(+), C (2)Pi(3/2u) and C (2)Pi(1/2u) states are determined to be 116591.1 +/- 6 c m(-1), 126883.9 +/- 3 cm(-1) and 128004.1 +/- 5 cm(-1), respectively, from which dissociation energies (D-0(+)) of 10603.7 +/- 6 cm(-1), 310.8 +/- 3 c m(-1), and 622.5 +/- 5 cm(-1) are obtained. The vibrational levels of the C (2)Pi(1/2u) state can be described by a Morse potential with w(e) = 58.9 /- 0.8 cm(-1) and w(e)x(e) = 1.40 +/- 0.27 cm(-1), respectively. Associativ e ionization and collisional ionization processes involving argon atom Rydb erg states induce spurious peaks in the PFI-ZEKE photoelectron spectrum. Wa ys to unambiguously identify these spurious peaks are discussed. (C) 1998 A merican Institute of Physics. [S0021-9606(98)02046-7].