Structure and energetics of Lin(OH)n−1 (n=2–5) clusters deduced from photoionization efficiency curves

Abstract

Ionization efficiency curves (IECs) were measured for Lin(OH)n−1 (n=2–5) clusters generated by reactions of laser-ablated lithium metal with water vapor, using photoionization time-of-flight mass spectrometry. The measured IECs are well-reproduced with a simulation involving Franck–Condon factors, enabling to identify the global-minimum structure of the clusters predicted in our theoretical study [Tanaka et al., J. Chem. Phys. 113, 1821 (2000)]. Hyperlithiated structures (HLS), in which an excess electron is delocalized, are identified for the cluster with n=2 and 3, while electron-localized or segregated structure (ELS) are for those with n=3–5. Adiabatic ionization energies were determined as 4.053±0.003 eV for HLS of Li2OH, 3.687±0.003 eV for HLS of Li3(OH)2, 4.133±0.003 eV for ELS of Li3(OH)2, and 3.418±0.009 eV for ELS of Li4(OH)3. The ionization energy of Li5(OH)4 was determined as 3.60±0.11 eV by a linear extrapolation of IEC. For Li3(OH)2, the energetics of two lowest-energy isomers is discussed based on the observed abundance ratio.