Photoelectron spectroscopy of lithium hydride anion

We present negative ion photoelectron spectra of the smallest stable molecular negative ion, the lithium hydride anion. Photoelectron spectra, recorded using 2.540 eV photons, are reported for the LiH(D) [X 1Σ+]+e−←LiH(D)−[X 2Σ+] transitions of 7LiH− and 7LiD−. Adiabatic electron affinities of 0.342±0.012 eV and 0.337±0.012 eV were determined for 7LiH and 7LiD, respectively. The experimentally determined electron affinities led to anion dissociation energy (D0) values of 2.017±0.021 eV for 7LiH− and 2.034±0.021 eV for 7LiD− relative to their Li[2S1/2]+H−(D−)[1S0] asymptotes. Franck–Condon analyses yielded the following molecular parameters for the ground state of 7LiH−: Be=6.43±0.18 cm−1, re=1.724±0.025 Å, and ωe=920±80 cm−1; and the following parameters for the ground state of 7LiD−: Be=3.62±0.06 cm−1, re=1.724±0.015 Å, and ωe=650±45 cm−1. In addition, we have observed the alkali hydride anions: 7LiH−2, 7LiD−2, Li2D−, NaD−, NaD−2, NaD−3, and NaD−4. No photodetachment signal was observed for the lithium dihydride anion, 7LiD−2, using 2.540 eV photons.