Roaming mechanisms, involving the brief generation of a neutral atom or molecule that stays in the vicinity before reacting with the remaining atoms of the precursor, are providing valuable insights into previously unexplained chemical reactions. Here, the mechanistic details and femtosecond time-resolved dynamics of H3+ formation from a series of alcohols with varying primary carbon chain lengths are obtained through a combination of strong-field laser excitation studies and ab initio molecular dynamics calculations. For small alcohols, four distinct pathways involving hydrogen migration and H2 roaming prior to H3+ formation are uncovered. Despite the increased number of hydrogens and possible combinations leading to H3+ formation, the yield decreases as the carbon chain length increases. The fundamental mechanistic findings presented here explore the formation of H3+, the most important ion in interstellar chemistry, through H2 roaming occurring in ionic species.

Roaming chemical reactions are often associated with neutral molecules. The recent findings of roaming processes in ionic species, in particular, ones that lead to the formation of H 3 + under strong-field laser excitation, are of considerable interest. Given that such gas-phase reactions are initiated by double ionization and subsequently facilitated through deprotonation, we investigate the strong-field photodissociation of ethanethiol, also known as ethyl mercaptan, and compare it to results from ethanol. Contrary to expectations, the H 3 + yield was found to be an order of magnitude lower for ethanethiol at certain laser field intensities, despite its lower ionization energy and higher acidity compared to ethanol. In-depth analysis of the femtosecond time-resolved experimental findings, supported by ab initio quantum mechanical calculations, provides key information regarding the roaming mechanisms related to H 3 + formation. Results of this study on the dynamics of dissociative halfcollisions involving H 3 + , a vital cation which acts as a Brønsted-Lowry acid protonating interstellar organic compounds, may also provide valuable information regarding the formation mechanisms and observed natural abundances of complex organic molecules in interstellar media and planetary atmospheres.

Interactions between metal centers in dimeric transition metal complexes (TMCs) play important roles in their excited-state energetics and pathways and, thus, affect their photophysical properties relevant to their applications, for example, photoluminescent materials and photocatalysis. Here, we report electronic and nuclear structural dynamics studies of two photoexcited pyrazolate-bridged [Pt(ppy(1) and [Pt(NDI-ppy)(μ-Ph 2 pz)] 2 (2, NDI = 1,4,5,8-naphthalenediimide), both of which have distinct ground-state Pt−Pt distances. X-ray transient absorption (XTA) spectroscopy at the Pt L III -edge revealed a new d-orbital vacancy due to the one-electron oxidation of the Pt centers in 1 and 2. However, while a transient Pt−Pt contraction was observed in 2, such an effect was completely absent in 1, demonstrating how the excited states of these complexes are determined by the overlap of the Pt (d z 2 ) orbitals, which is tuned by the steric bulk of the pyrazolate R-groups in the 3-and 5-positions. In tandem with analysis of the Pt−Pt distance structural parameter, we observed photoinduced electron transfer in 2 featuring a covalently linked NDI acceptor on the ppy ligand. The formation and subsequent decay of the NDI radical anion absorption signals were detected upon photoexcitation using optical transient absorption spectroscopy. The NDI radical anion decayed on the same time scale, hundreds of picoseconds, as that of the d-orbital vacancy signal of the oxidized Pt−Pt core observed in the XTA measurements. The data indicated an ultrafast formation of the charge-separated state and subsequent charge recombination to the original Pt(II−II) species.

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