Small Tunneling Splitting of Methyl-Group and <i>T</i>_1ρ of Protons in Pentamethylbenzene

Abstract

Temperature dependence of T 1 , T 1ρ and T D 1 of protons have been measured in pentamethylbenzene between 300 K and 8 K. The anomalous behavior of T 1 and T 1ρ between 80 K and 40 K can be understood as the effect of the tunneling motion of methyl-groups. By using a simple model of relaxation and the data of T 1ρ , the tunneling splitting of methyl-group was estimated to be about 500 kHz.