Anion solvation at the microscopic level: Photoelectron spectroscopy of the solvated anion clusters, NO~-(Y)_n, where Y=Ar, Kr, Xe, N_2O, H_2S, NH_3, H_2O and C_2H_4(OH)_2

摘要

The negative ion photoelectron spectra of the gas-phase, ion-neutral complexes; NO~-(Ar)_n = 1-14, NO~-(Kr)_1, NO~-(Xe)_n = 1-4, NO~-(N_2O)_n = 3-5, NO~-(H_2S)_1, and NO~-(EG)_1 [EG = ethylene glycol] are reported herein, building on our previous photoelectron studies of NO~-(N_2O)_(1,2) and NO~-(H_2O)_(1,2). Anion solvation energetic and structural implications are explored as a function of cluster size in several of these and as a result of varying the nature of the solvent in others. Analysis of these spectra yields adiabatic electron affinites, total stabilization (solvation) energies, and stepwise stabilization (solvation) energies for each of the species studied. An examination of NO~-(Ar)_n = 1-14 energetics as a function of cluster size reveals that its first solvation shell closes at n = 12, with an icosahedral structure there strongly implied. This result is analogous to that previously found in our study of O~-(Ar)_n. Inspection of stepwise stabilization energy size dependencies, however, suggests drastically different structures for NO~-(Ar)_2 and O~-(Ar)_2, the former being "Y" shaped, and the latter being linear. While stepwise stabilization energies usually provide good estimates of ion-single solvent dissociation energies, in the cases of NO~-(Ar)_1, NO~-(Kr)_1, and NO~-(Xe)_1, it is possible to determine more precise values. A plot of these anion-solvent dissociation energies shows them to vary linearly with rare gas atom polarizability, confirming the dominance of an ion-induced dipole interaction in these complexes. Extrapolation of this trend permits the estimation of NO~-...(rare gas atom) interaction energies for helium, neon, and radon, as well. The relative strengths of the molecular solvents, N_2O, H_2S, NH_3, H_2O, and EG are reflected in their stepwise stabilization energies and in the degree of broadening observed in their photoelectron spectra.