Photoinduced electron transfer and solvation dynamics in aqueous clusters: comparison of the photoexcited iodide-water pentamer and the water pentamer anion

Abstract

Upon photoexcitation of iodide-water clusters, I(-)(H(2)O)(n), an electron is transferred from iodide to a diffuse cluster-supported, dipole-bound orbital. Recent femtosecond photoelectron spectroscopy experiments have shown that, for photoexcited I(-)(H(2)O)(n) (n≥ 5), complex excited-state dynamics ultimately result in the stabilization of the transferred electron. In this work, ab initio molecular dynamics simulations of excited-state I(-)(H(2)O)(5) and (H(2)O)(5)(-) are performed, and the simulated time evolution of their structural and electronic properties are compared to determine unambiguously the respective roles of the water molecules and the iodine atom in the electron stabilization dynamics. Results indicate that, driven by the iodine-hydrogen repulsive interactions, excited I(-)(H(2)O)(5) rearranges significantly from the initial ground-state minimum energy configuration to bind the excited electron more tightly. By contrast, (H(2)O)(5)(-) rearranges less dramatically from the corresponding configuration due to the lack of the same iodine-hydrogen interactions. Despite the critical role of iodine for driving reorganization in excited I(-)(H(2)O)(5), excited-electron vertical detachment energies appear to be determined mostly by the water cluster configuration, suggesting that femtosecond photoelectron spectroscopy primarily probes solvent reorganization in photoexcited I(-)(H(2)O)(5).

Decay dynamics of nascent acetonitrile and nitromethane dipole-bound anions produced by intracluster charge-transfer

“…16,23 The eBE of the nitromethane DBS was measured to be approximately 10 meV in RET 16 and PES 34 experiments; interaction between the nitromethane anion and a neutral iodine atom may somewhat increase the VDE of the TNI complex. 16,39,[65][66][67][68] The narrow feature E with its VDE of approximately 20 meV is consistent with this description and is therefore identified as the DBS of nitromethane. The positive value of the associated β 2 anisotropy parameter supports the assignment of this feature as described in Sec.…”

“…25 Iodine is expected to minimally perturb the acetonitrile DBS, and the binding energy of neutral iodine to molecules and cluster anions has been estimated as approximately 50 meV. 59,[65][66][67][68] Thus, the narrow and weakly bound (VDE = 20 meV) feature C 2 can reasonably be assigned to direct photodetachment of the dipole-bound acetonitrile anion by the probe pulse. The asymptotic anisotropy values depicted in Figure 7(a) also support this assignment, as the β 2 value of unity matches previously reported values 69 while the β 4 value of zero is consistent with single-photon photodetachment.…”

RASPT2 Analysis of the F–(H2O)n=1–7 and OH–(H2O)n=1–7 CTTS States

“…However, the whole system made of such an anion embedded in a water cluster can support electronic excited states, which are broadly delocalized on the solvent molecules and show a strong resemblance to the solvated electron ground state for water clusters of comparable size. 1 Such excited states are referred to as charge-transfer-to-solvent (CTTS) states. Their properties have been investigated experimentally with various techniques.…”

“…Regarding halides embedded in water clusters, excited state studies have been performed in the case of I – (H 2 O) n . In particular, ab initio molecular dynamics simulations based either on RASSCF , or on DFT , calculations have been used to follow the CTTS state relaxation characterized by iodine atom detachment from the negatively charged water cluster. In solution, the relaxation of Cl – and I – CTTS states has been investigated by means of model potential techniques. , …”

Relaxation dynamics of the mass-selected hydrated Auride ion (Au−)

“…Here, the initial drop in the binding energy of the excited state was attributed to the repulsive interaction between solvent and detached elec trons induced by the rapid geometric rearrangement of water molecules in the cluster just after photoexcitation by pump pulse . [18,19].…”