Iodide solvation in tetrahydrofuran clusters: I ^-(THF) _n (1 ≤ n ≤ 30)

The solvent structure and binding motif of iodide-doped tetrahydrofuran clusters, I(THF) _n (1n30) are investigated with anion photoelectron imaging, molecular dynamics simulations, and ab initio calculations of vertical detachment energies. Experimentally, a dramatic decrease in the iodide differential stabilization energy and concomitant change in the mass spectrum at n=9 suggest that the first solvation shell closes at n=9-10 THF molecules, in rough agreement with the theoretical result of n=7-9 determined from the computation of relaxed and unrelaxed solvent distribution densities. Analysis of the vertical detachment energy vs. inverse cluster radius suggests the iodide atom is maximally coordinated around n=9. Decomposition of the interaction energies of I(THF), its vertically-detached complement, and the (THF) ₂ dimer, employing the absolutely-localized molecular orbital energy decomposition analysis (ALMO EDA) scheme, highlights the dependence of electron binding and detachment on both electrostatics and polarization, with direct evidence of the fundamental importance of polarizability to a description of detachment. Experimental and theoretical evidence for an anionic electronically excited state is also presented; computed excitation energies and their attendant characters are discussed. The results are interpreted within the framework of the inefficient packing that occurs in bulk neat THF.