  The tunneling transport theory developed in Phys. Rev. B {\bf 76}, 115102
(2007) is applied to molecular devices made of alkyl chains linked to gold
electrodes via amine groups. Using the analytic expression of the tunneling
conductance derived in our previous work, we identify the key physical
quantities that characterize the conductance of these devices. By investigating
the transport characteristics of three devices, containing 4, 6, and 8 methyl
groups, we extract the dependence of the tunneling conductance on the chain's
length, which is an exponential decay law in close agreement with recent
experimental data.
