Unraveling the Electronic Structures of Platinum-Bromine Superhalogens: Photoelectron Spectroscopy of PtBr_n^- (n = 2-5)

We report a systematic investigation of the electronic structures and photodetachment dynamics of platinum bromide anions, PtBrn- (n = 2-5), using cryogenic anion photoelectron spectroscopy combined with quantum chemical calculations. High-resolution spectra acquired at 193 nm provide accurate adiabatic and vertical detachment energies (ADEs and VDEs), which show excellent agreement with theoretical values. The measured ADEs, corresponding to the electron affinities (EAs) of the neutral species, increase monotonically with increasing bromine coordination, establishing the superhalogen nature of these species. Notably, PtBr5- exhibits an unusually broad low energy feature in the photoelectron spectrum, attributed to resonant autodetachment. Complementary analyses-including natural population analysis (NPA), frontier molecular orbital (FMO) mapping, and charge density difference (CDD) visualization-reveal the orbital origins of the observed detachment channels and the associated charge redistribution. Bonding characteristics and relative stabilities are further assessed through fuzzy bond order (FBO) and natural adaptive orbital (NAdO) analyses. These findings provide a more comprehensive understanding of the electronic structures and bonding of platinum halides, offering insights relevant to the stability and ligand-exchange reactivity of transition metal superhalogens.