  We present a detailed $^{2}$H NMR characterization of molecular mobility of
1-butene and n-butane propagating through the microporous ZIF-8, a zeolitic
imidazolate framework renowned for its outstandingly high stability and
separation selectivity of various. The experimental characterization of
n-butane and 1-butene diffusivity in ZIF-8 on the molecular scale is provided
for the first time. With $^{2}$H NMR spin relaxation analysis we have
elucidated the motional mechanism for 1-butene and n-butane guests trapped
within ZIF-8 framework and derived kinetic parameters for each type of motion.
The characteristic times for microscopic translational diffusion and activation
barriers (E$_{C4H10}$ = 34 kJ mol$^{-1}$, E$_{C4H8}$ = 32 kJ mol$^{-1}$) for
n-butane and 1-butene diffusivities have been elucidated. Finally, we show that
$^{2}$H NMR technique is capable to provide reliable information on microscopic
diffusivity in the ZIF-8 MOF even for molecules with slow diffusion rates
(<10$^{-14} m^{2} s^{-1}$).
