Inelastic Tunneling Current Equation help

[Huor Earfalas]

In this paper ("Molecular Vibration Spectra by Inelastic Electron Tunneling" by J. Lambe & R.C. Jaklevic Phy.Rev. Vol 165, Article 3), the author showed that when external voltage is applied across a metal-insulator-metal, the current passing through the insulator is shown to be:

I(V) = N(\frac{dj}{dV})[\frac{4\pi me}{\bar{h}^2\phi}]ln(\frac{l}{r0})... (formulae continues)

I am unfamiliar with the parameter r0, which is called, in the paper, the cut-off distance in the vicinity of the molecule. I believe this is a constant and unique to different molecules, if so, where can I find data regarding this? I greatly appreciate your time and effort for explaining this term to me :)

EDIT: Unfortunately I was not able to post link since I am new.

 

[azntoon]

The article I mentioned is "Molecular Vibration Spectra by Inelastic Electron Tunneling" by J. Lambe & R.C. Jaklevic, Physical Review Volume 165, Number 3.The parameter r0 is a cut-off distance in the vicinity of the molecule. It represents the distance from the molecular center when the electron-electron interaction is negligible. This is a constant and unique to different molecules, and can be determined experimentally. For example, the cut-off distance for the water molecule is 6.1 Å (0.6nm).