We have presented a successful demonstration of frequency-resolved ultrafast transient vibrational action spectroscopy on cryogenically cooled fac-Re(CO)3(CH3CN)3 + ions. Although the very intense carbonyl stretch features in the metal complex provided an ideal test system, the scheme is generally applicable. As another example, the transient absorption spectrum of protonated caffeine (C8H10N4O2-H + ) in the fingerprint region is presented in Fig. . The current demonstration also lays the foundations for acquisition of 2D IR and transient UV/Vis-IR spectra on dilute molecular ion ensembles, which could be highly impactful tools for the study of chemical structures and reaction dynamics. The general strategies presented here can also be applied to dilute neutral systems. For neutrals, an additional UV/Vis pulse is required to generate an action response, such as photofragmentation or ionization, that is modulated by the preceding IR pulse sequence.