Structure, energetics and vibrational spectra of protonated chlortetracycline in the gas phase: An experimental and computational investigation

► IRMPD spectra of protonated chlortetracycline have been obtained. ► Electronic structure calculations of possible isomers and tautomers are presented. ► Computed vibrational spectra and experimental IRMPD spectra have been compared. ► Probable structure identification of protonated chlortetracycline has been made. ► Future experiments to aid in structural assignment have been proposed.