Strong ortho/para effects in the vibrational spectrum of Cl-(H2)

The predissociation spectrum of the Cl-35(-)(H-2) complex is measured between 450 and 800 cm(-1) in a multipole radiofrequency ion trap at different temperatures using the FELIX infrared free electron laser. Above a certain temperature, the removal of the Cl-(p-H-2) para nuclear spin isomer by ligand exchange to the Cl-(o-H-2) ortho isomer is suppressed effectively, thereby making it possible to detect the spectrum of this more weakly bound complex. At trap temperatures of 30.5 and 41.5 K, we detect two vibrational bands of Cl-(p-H-2) at 510(1) and 606(1) cm(-1). Using accurate quantum calculations, these bands are assigned to transitions to the inter-monomer vibrational modes (v(1),v(2)(l2)) = (0, 2(0)) and (1, 2(0)), respectively. (C) 2021 Author(s).

Automated summary

The predissociation spectrum of the Cl-35(-)(H-2) complex was measured in a multipole radiofrequency ion trap at different temperatures using the FELIX infrared free electron laser. Removal of the Cl-(p-H-2) para nuclear spin isomer by ligand exchange to the Cl-(o-H-2) ortho isomer above a certain temperature allows for detecting the spectrum of the more weakly bound complex. Two vibrational bands of Cl-(p-H-2) at 510(1) and 606(1) cm(-1) were detected at trap temperatures of 30.5 and 41.5 K.