Can you tell me which one is correct

better interpretation of experimental data (at) structural level

OR

better interpretation of experimental data (on) structural level

regards

I prefer this:

better interpretation of experimental data at the structural level

Or use the indefinite article:

better interpretation of experimental data at a structural level

The choice between "at" or "on" depends on the rest of the sentence and the point you're making; "structural" is an adjective -- without it, it's clear you can be "at" a level or "on" a level...