Below the molecular scale; smaller than a molecule(adjective)
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Use "submolecular" in a sentence
"That device is capable of rearranging matter on a submolecular level."
"Yes, but will your existence be the truth, the whole truth, and nothing, nothing, nothing but the truth down to the submolecular, quantum level, so help you the American Literary Taliban you know, God."
"Hopefully with the help of smart scientists working at the submolecular level, the scariest headlines we will likely read in the future will be "Terrorist Plot Foiled" rather than the ones we saw following the tragic events of Sept. 11, 2001."