Comparison of computed IR absorption spectrum of protonated diglycine (top), with experimental IRMPD (gray shaded) and cryogenic (black line) IR spectra of the same molecule (bottom). Adapted with permission from Kamrath, M.Z., Garand, E., Jordan, P.A., Leavitt, C.M., Wolk, A.B., Stipdonk, M.J.V., et al.: Vibrational Characterization of Simple Peptides Using Cryogenic Infrared Photodissociation of H2-Tagged, Mass-Selected Ions. J Am Chem Soc. 133, 6440–6448 (2011). Copyright 2011 American Chemical Society.