We investigate molecular passage through a geometrical barrier. We assume that the barrier is a stochastic gate so that the passage rate depends on its fluctuating nature and on the molecular size. We calculate the dependence of the passage rate Keffon relaxation rate of the gate radius and therefore on the solvent viscosity η. Two cases are solved: an open-or-closed gate and an harmonic gate. The latter is shown to lead to the experimentally observed fractional power law dependence of Keffon η.