In this paper, we calculate the dynamical exponents of diffusion, d(w)
/d(f) and d(s), on a percolation cluster at p(c) with no loops, for th
e square and simple cubic lattices by the method of spectral analysis
of the transition probability matrix. Results show that d, varies sign
ificantly with the spatial dimension, unlike in conventional percolati
on, but the Alexander-Orbach scaling relation d(s) = 2d(f)/d(w) still
holds. Thus it rules out the possibility that this scaling relation fa
ils for all loopless fractals because of trapping.