spectrum. These doublets and most other features can be explained by assuming equal population of both nearly degenerate cis and trans isomers of ZrO(OH)2ˉ. Electronic structure calculations find the two isomers to have nearly identical electron affinities but slightly different vibrational frequencies in several low frequency, FC active modes. Hence, only one vibrational origin is observed, peak A at 1.1616 (7) eV, but peaks B and C are split by 4 cm -1 because the vibrational frequency of the 12 umbrella mode is 65 cm -1 for the cis isomer and 69 cm -1 for the trans isomers. The FC simulations for the two isomers are shown by the red (cis) and blue (trans) sticks in Figure . While the fit is not perfect, it does reproduce most of the experimental features and shows that there is more FC activity from the trans than from the cis isomer.