C-13 nuclear spin-lattice relaxation in CH3 compounds



: Punkkinen M

: 2001

 Molecular Physics Reports

: QUANTUM ATOMIC AND MOLECULAR TUNNELLING IN SOLID

: MOLECUL PHYS REP

: 31

: 92

: 99

: 8

: 83-87671-78-9

: 1505-1250


Spin-lattice relaxation of (CH3)-C-12 groups is reviewed in terms of the four population combinations the proton magnetization M-H, tunnelling energy TE, rotational polarization and dipolar energy. Special emphasis is paid to the question when the time-dependence of these quantities can be expressed by one or at most two exponentials. The presence of 13 C nuclei in methyl groups introduces additional transition rates and population combinations. In the slow motion regime only one additional combination, the 13 C magnetization M-C, is necessary. Coupled equations are derived for the time-dependence of MC, MH and TE near the level crossings, where only the "resonant" transition rates need to be considered. Their solution for exact level crossings indicate that the initial relaxation rate of M-C, after the saturation of either M-C or M-H, should show maxima at omega(1) = omega(C), omega(1) = omega(H) + omega(C) and omega(1) = omega(H) - omega(C), where the omega symbols refer to the methyl tunnelling frequency and the carbon and proton resonance frequencies (in angular units), respectively. Similar but smaller effects should be observed in the M-H relaxation.



Last updated on 13/10/2025 02:24:24 PM