Temperature-Dependent Infrared Photodissociation Spectroscopy of (CO₂)₃⁺ Cation

Infrared photodissociation spectra of He-buffer-gas-cooled (CO₂)₃⁺ were measured at ion trap temperatures of 15, 50, 150, and 280 K. Electronic structure calculations at the mPW2PLYPD/aug-cc-pVDZ level were performed to identify the structures of the low-lying isomers and to assign the observed spectral features. The experimental and calculated infrared spectra show that the (CO₂)₃⁺ cations formed in the source are primarily dominated by the charge partially delocalized C₂O₄⁺ motif, in which the positive charge is partially delocalized over the two CO₂ molecules. Thermal heating at elevated internal temperature supplies sufficient energy to overcome the isomerization barriers and gives access to the charge completely delocalized (CO₂) _n⁺ ( n = 3) motif, in which the positive charge is almost completely delocalized over all of the constituent CO₂ molecules.