A spectrometer is described allowing the measurement of transverse relaxation times ≳ 30 ms at 40 kc/s and of longitudinal relaxation times ≳ 0,1 s within the range of 40 kc/s to 1 Mc/s at any frequency. The relative large sample volume of 800 cm3 and the premagnetisation of the sample in a strong magnetic field (⩽ 800 Oe) assure a sufficient signal intensity.

The longitudinal proton relaxation time in aqueous solutions of Mn2+-ions determined in a temperature range of 15…95°C at frequencies between 15 kc/s and 1 Mc/s indicates an important influence of the hyperfine coupling. The experimental results are in good agreement with the result of the calculations of SAMES and MICHEL in Part I of this paper. The doubling of electron relaxation time and the decrease of scalar contribution of the relaxation rates for high temperatures during passing from high to low fields is evident. Furthermore, the theoretically predicted large range of validity of the weak field formula which describes the experimental results up to 1 Mc/s is noteworthy. However, it is not possible to give a reasonable interpretation of the experimental results by means of the theory of Solomon and Bloembergen.

From the experimental results the till now always assumed temperature independence of the coupling constant of the scalar interaction in aqueous solutions of Mn2+-ions could clearly be proved between 0 and 100°C.

Studies on solutions of Mn2+-ions in formic acid and methanol, respectively, show that the dipole contribution of the relaxation rates for sufficient long correlation times will be also affected by the hyperfine coupling during passing from high to weak magnetic fields.