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 (1) Sigma(+)]+e(-) <-- LiH(D)(-)[X (2) Sigma(+)] transitions of (LiH-)-Li-7 and (LiD-)-Li-7. Adiabatic electron affinities of 0.342+/-0.012 eV and 0.337+/-0.012 eV were determined for (LiH)-Li-7 and (LiD)-Li-7, respectively. The experimentally determined electron affinities led to anion dissociation energy (D-0) values of 2.017+/-0.021 eV for (LiH-)-Li-7 and 2.034+/-0.021 eV for (LiD-)-Li-7 relative to their Li[S-2(1/2)]+H-(D-)[S-1(0)] asymptotes. Franck-Condon analyses yielded the following molecular parameters for the ground state of (LiH-)-Li-7: B-e=6.43+/-0.18 cm-(1), r(e)=1.724+/-0.025 Angstrom, and omega(e)=920+/-80 cm(-1); and the following parameters for the ground state of (LiD-)-Li-7: B-e=3.62+/-0.06 cm(-1), r(e)=1.724+/-0.015 Angstrom, and omega(e)=650+/-45 cm(-1). In addition, we have observed the alkali hydride anions: (LiH2-)-Li-7, (LiD2-)-Li-7, Li2D-, NaD-, NaD2-, NaD3-, and NaD4-. No photodetachment signal was observed for the lithium dihydride anion, (LiD2-)-Li-7, using 2.540 eV photons.