The gas phase equilibria Ba + LnX = BaX + Ln (Ln = Sm, Eu, Yb; X = Cl, Br, I) were investigated by Knudsen effusion mass spectrometry using a low energy of ionizing electrons to avoid fragmentation processes. The BaX molecules were used as references with well-established bond energies. The atomization enthalpies Delta H-at(0)degrees of the LnX molecules were determined to be 427 +/- 9 (SmCl), 409 +/- 9 (EuCl), 366 +/- 9 (YbCl), 360 +/- 10 (SmBr), 356 +/- 13 (EuBr), 316 +/- 9 (YbBr), 317 +/- 10 (SmI), 293 +/- 10 (EuI), and 283 +/- 10 (YbI) kJ.mol(-1).