The far infrared absorption spectrum of the lithium perchlorate/benzo-15-cr
own-5 complex separated from various solvents has been investigated in the
250 similar to 590 cm(-1) region. It has been found that the change in the
medium used for the preparation of the complex probably leads to the change
in the far infrared shift. A linear function of far infrared absorption ba
nd versus lithium isotope abundance in the complex was discovered. The far
infrared absorption band of the complex containing 100% Li-6 could be deter
mined by extrapolation. A concept of relative reduced partition function ra
tio was proposed for the first time in order to calculate approximately the
isotope effect of lithium by use of the data of the far infrared spectra.