On acid surfaces, trimethylphosphine (TMP) forms either Bronsted or Le
wis site adducts, TMPH(+) or TMP:L, respectively. In TMPH(+), the P-31
magnetization decay is practically monoexponential and the P-31 spin-
lattice relaxation rate (1/T-1) is not thermally activated. In TMP:L,
the magnetization decay is biexponential and the relaxation rate is th
ermally activated. Using the known internuclear distances in TMPH or T
MPH(+), it is shown that the relaxation rates can be accounted for by
using the homo- and heteronuclear (intramolecular) contribution rates.
The only adjustable parameter is the preexponential factor in the cor
relation time (tau(0)). tau(0) is 10(-11) s for the PH vector reorient
ation and 10-(13) s for the H-H (methyl) vector rotation in TMP:L. It
is 10(-7) s for the PHC reorientation in TMPH(+). It is observed that
the resonance frequency in TMPH(+) or TMP:L is temperature independent
, ruling out chemical exchange. In one case only, (TMPH(+) on dealumin
ated H-Y zeolite) a change in the isotropic chemical shift with temper
ature has been observed.