The molecules Li3H and Li4H have been identified in mass-spectrometric measurements over solutions of hydrogen in liquid Li, and the gaseous equilibria of the reactions: Li3H + Li = Li2H + Li-2, Li3H + Li-2 = Li2H + Li-3, Li3H + Li = LiH + Li-3, Li3H + LiH = 2Li(2)H, and Li4H + Li-2 = Li3H + Li-3 have been measured. Density functional calculations of LinH molecules (n = 3-6) provide structures, vibrational frequencies, ionization energies, and free energy functions of these molecules, and these are used to estimate the enthalpies of these reactions and the atornization energies of Li3H (119.4 kcal/mol) and Li4H (151.8 kcal/mol). (C) 2004 American Institute of Physics.