The second-order shifts of the Rb-87 1/2 --> - 1/2 NMR transitions hav
e been measured in RbSCN above and below T-c=435 K for crystal rotatio
ns around the a, b, and c axes. Whereas below T-c the Rb-87 electric-f
ield gradient (EFG) and chemical shift tensors are compatible with the
Rb site symmetry as given by the orthorhombic space group D-2h(ll)(Pb
cm), this is not the case for the EFG data above T-c. The results show
that the symmetry of the high-temperature tetragonal phase is dynamic
ally broken on the Larmor frequency (10(-8) s) time scale whereas symm
etry-breaking terms are averaged out on the ''site'' splitting, domain
splitting, and chemical shift tenser (similar or equal to 10(-2)-10(-
3) s) time scales. Rb-87 NMR thus allows for an observation of the pha
se transition in RbSCN in the ''slow motion'' regime where the high-te
mperature phase is seen to consist of a large number of orthorhombic m
icrodomains with lifetimes longer than 10(-7) s and shorter than 10(-3
) s.