H-2 NMR spectra and interpretations are presented on two samples of deuterium-labeled benzene that have been adsorbed on a major soil component, Ca-montmorillonite clay. Spectra were obtained on the samples with two different benzene loading levels over a wide temperature range and using two values of the quadrupolar echo delay period. Computer simulations of line shapes resulting from various forms of local motion of C-H-2 moieties provide useful guidelines for interpreting the experimental results. The results suggest that absorbed benzene molecules first form pi-complexes with Ca2+ in the interlayer space of the clay with an adsorption enthalpy of 42 +/- 4 kJ/mol at temperatures at or below -75 degrees C. The adsorbed molecules undergo small-angle wobbling of the C6 axis accompanied by rapid discrete jumps about the C6 axis. At higher temperatures, benzene molecules start to perform large-angle wobbling of the C6 axis with extremely fast jumps around the axis, and eventually desorb from Ca2+ to tumble freely in the interlayer space of the clay. The enthalpy and entropy changes between different motional states were obtained from the variable temperature studies. The activation energies of relevant molecular motions were also estimated. This approach is attractive for elucidation of the detailed motional behaviors of organic pollutants adsorbed in soil.