PHOTOELECTRON-SPECTROSCOPY OF LITHIUM HYDRIDE ANION

We present negative ion photoelectron spectra of the smallest stable m olecular negative ion, the lithium hydride anion. Photoelectron spectr a, 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, re spectively. The experimentally determined electron affinities led to a nion dissociation energy (D-0) values of 2.017+/-0.021 eV for (LiH-)-L i-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 follow ing 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.