US EPA

5452417 

Journal Article 

MAGNETIC RESONANCE LINE SHAPES IN SOLIDS .2. MOLECULAR MOTION IN METHYL CHLOROFORM AND METHYL TRICHLOROSILANE 

Mcintyre, HM; Johnson, CS 

1971 

Yes 

Journal of Chemical Physics
ISSN: 0021-9606
EISSN: 1089-7690 

55 

1 

345 

English 

10.1063/1.1675528 

WOS:A1971J783100045 

Line shape and spin-lattice relaxation measurements are reported for methyl chloroform and methyl trichlorosilane. Spectra in the line shape transition region for CH3CCl3 are compared with exact line shape calculations by means of the apparent second moments to obtain 4.3±0.2 kcal/mole for the energy of activation for methyl rotation. Proton T1 measurements at 30 MHz give activation energies of 3.7 kcal/mole for CH 3CCl3 and 1.3 kcal/mole for CH3SiCl 3, but the relaxation mechanisms are not completely understood. It is argued that the CH3CCl3 molecule rotates as a unit above 110°K. Line shapes and relaxation rates have also been determined for CH3CCl3 and CH3SiCl3 in perchloropropene glass where resolution is greatly enhanced in order to search for the effects of tunneling. The T1 measurements above 77°K indicate relatively free molecular motion and distinctly non-Arrhenius behavior. The spectra of these systems at 4.2°K are characteristic of rigid and rapidly rotating methyl groups for CH3CCl3 and CH 3SiCl3, respectively. These results are consistent with the calculations of Apaydin and Clough for low and high tunneling frequencies but their line shapes for intermediate frequencies have not been confirmed.