Exploring direct photodetachment and photodissociation-photodetachment dynamics of platinum iodide anions (PtI_n⁻, n = 2-5) using cryogenic photoelectron spectroscopy

The direct photodetachment and two-photon photodissociation-photodetachment processes of a series of PtI_n⁻ (n = 2-5) anions were systematically studied using cryogenic anion photoelectron spectroscopy and first-principles electronic structure calculations. The adiabatic/vertical detachment energies (ADEs/VDEs) of these anions were determined from their 193 nm photoelectron (PE) spectra, i.e., 3.54/3.63, 4.04/4.09, 4.33/4.36, and 4.37/4.41 eV for n = 2-5, respectively, and well reproduced by B3LYP-D3(BJ)/aug-cc-pVTZ-pp calculations. As the coordination number increases, the electron affinity (EA) of PtI_n^• (n = 2-5) neutrals (equivalent to the corresponding anion’s ADE) gradually increases, exceeding the EA of Cl at n = 3 and exhibiting superhalogen characteristics for n ≥ 3. Meanwhile, the ground state transition contributed from detaching electrons in the highest occupied molecular orbital gradually evolves from the central metal Pt to the iodine ligands. For the PtI₃⁻ anion, besides one-photon direct detachment, four distinct two-photon photodissociation-photodetachment channels were identified, and the competition between them was discussed.