A re-analysis of the vacuum ultraviolet absorption spectrum of I2, Br2, and ICl using ionization energies determined from their ZEKE-PFI photoelectron spectra

Abstract

The vacuum ultraviolet absorption spectra of I₂, Br₂ and ICl have been re-analysed using new data from the zero kinetic energy-pulsed field ionization (ZEKE-PFI) photoelectron spectra of all three molecules, and the (2 + 1) resonance enhanced multiphoton ionization (REMPI) spectrum of ICl. A common pattern of absorption intensities emerges in which all transitions to states which have appreciable singlet character are strong. Thus, in all three molecules, strong transitions are observed to four np and six nf Rydberg series based on the X[²Π_3/2]_g and X[²Π_1/2]_g states of the molecular ions, to two ns and six nd states in ICl and to two ns states based on the A[²Π_3/2]_u and A[²Π_1/2]_u states of the ion in Br₂. The Ω values of some of the Rydberg series have been determined directly from the (2 + 1) REMPI spectrum of ICl.