All collision-induced dissociation (CID) experiments were conducted using a Thermo Scientific LTQ XL ion trap mass spectrometer. Adipic acid clusters were generated by electrospray ionization (ESI) of a solution of 5 mM solution of adipic acid in water with 0.1 wt.% formic acid. Ammonia was presumably sourced from the atmosphere or trace contaminants in the solute or solvent. For CID experiments, the ammonium-adipic acid cluster was isolated and activated with enough Normalized Collision Energy (NCE, a nonstandard unit that provides a relative energy scale) to dissociate approximately 90% of the parent ion. For MS n experiments, this process was repeated for the specified number of CID cycles. Clusters containing deuterium were generated by ESI of a 5 mM adipic acid in deuterium oxide with 0.1% formic acid solution.