Zasorin and Rambidi recently determined two vibrational frequencies of aluminum trichloride with the aid of high-temperature gas electron-diffraction data. This work has inspired us to extend previous studies of accurate determinations of force fields from experimental mean amplitudes with particular attention to these quantities at high temperatures. It is concluded that the required accuracies of mean amplitudes to be employed in reasonably accurate force-constant determinations decrease substantially when the temperature is increased. If the required error limits for l2(Cl·Cl) in AlCl3 are ± 0.0011 Å at absolute zero, they increase to ± 0.0034 Å at 298 °K, and ± 0.0043 Å at 800 °K. These figures correspond to ζ1z(E'×E') = 0.7 ±0.1 according to the present analysis. For the Coriolis ζ-constant in AlCl3 no experimental value is available, but a magnitude around 0.7 in accord with the present calculations was found to be probable from studies of mass-dependence on the ζ-values. It is also concluded that the situation for shrinkage effects in force-field determinations is substantially more favourable when high-temperature data are available than is the case for room-temperature data. © 1969.
