Structural isomerism in the I-2-Ar Van der Waals complex studied by ZEKE-PFI spectroscopy: Evidence for both linear and T-shaped isomers

Evidence for the existence of two structural isomers of the I-2-Ar Van der Waals complex has been obtained from REMPI spectroscopy and ZEKE-PFI (zero kinetic energy-pulsed field ionisation) spectroscopy. The mass-resolved REMPI spectrum of the complex in the [(2) Pi(3/2)](c) 7s; 2(g) Rydberg state shows two overlapping vibrational progressions which have been assigned to excitation of the T-shaped and linear isomers. The two-colour ZEKE-PFI spectrum of the ground electronic state of the ion recorded via a number of vibrational levels in the [(2) Pi(3/2)](c) 7s; 2(g) Rydberg state show two well separated vibrational progressions. The measured difference of 43 cm(-1) in the band origins for the two progressions provides an indication of the relative stabilities of the two isomers in the ion, with the linear isomer being the more weakly bound.