The quantitative determination of 6Li and 'Li in Rhine water and the isotopic distribution in a number of commercial lithium salts have been evaluated by the application of FD mass spectrometry in combination with a multichannel analyser. 6Li and 'Li were determined quantitatively (with a total error of 5 % ) by the isotopic dilution method using 6Li-enriched lithium fluoride as the standard. The results obtained showed that the isotopic distribution in lithium salts deviated from the mean natural abundance in contrast to the natural distribution found in the case of samples of Rhine water.The results of a number of theoretical studies on lithium compounds have been reported. For example, the information obtained from accurate ab initio configuration interaction calculations has been used to obtain the potential energy curves of the ground state of LiH-and LiH.2 For LiH the calculated values of the bond length, dissociation energies, and spectroscopic constants, obtained from the potential energy curve, were within 1 % of the experimental values. An SCF correlation diagram has been reported for low-lying linear and bent states of Li2H, and SCF potential curves have been computed for the collinear reactions H + Liz and Li + LiH.3 The results indicated that Li2H, at the present an unknown molecule, may be obtained from the interaction of Li and LiH.Pressure-composition-temperature data have been collected for the Li-LiD system over the ranges 0-750 Torr, 1-99 mol YO LID, and 705-871 "C by measuring the equilibrium deuterium pressures over encapsulated Li-LiD mixture^.^ The information obtained enabled a series of five Pb, us. NLiD isotherms to be con-