Lennard-Jones diagram - what is on the x-axis?

I have a Lennard-Jones diagram here where I can't figure out, what is on the x-axis.


[![enter image description here](https://i.stack.imgur.com/nKfIb.png)](https://i.stack.imgur.com/nKfIb.png)
G. Ertl, Angew. Chem. Int. Ed. 2008, 47


We are looking at a diagram for a molecule $\mathrm A\_2$ composed of two $\mathrm A$ atoms that comes into close contact with a surface.


* If the molecule $\mathrm A\_2$ forms a bond with the surface, a shallow minimum ($\mathrm A\_{2,ad}$) is reached.
* $E\_{diss}$ is the dissociation energy needed to seperate/dissociate the two $\mathrm A$ atoms from each other (breaking the molecule). In this form (as two individual atoms), they could both seperately bind to the surface, resulting in much stronger bond formation $2 \mathrm A\_{ad}$. This would be called *chemisorption*, if I'm not wrong.
* Now combinding these two processes, we would have *dissociative chemisorption*. The crossing point between the two curves markes the activation energy of this.


This was just an explanation of the graph. My question is, how I should understand the horizontal dimension here - the x-axis. On a google search many diagrams pop up, but never with the dissociation included. Many of those as well as the [Wikipedia article](https://en.wikipedia.org/wiki/Lennard-Jones_potential) about Lennard-Jones potential show the x-axis as a distance between atoms - the interatomic distance $r$.


I cannot make sense of that on the diagram I am showing above. The distance between atoms should be *smaller* for the molecule than for the seperated atoms. What is on the x-axis in this case?




Ahh, silly me. The x-coordinate is of course just the distance between the $\mathrm A$ atoms / $\mathrm A\_2$ molecule and the **surface**, to which they bind. This diagram doesn't show the interaction between $\mathrm A$ atoms but between them and the surface. I will close this question as solved.


 3