Two-Dimensional Infrared Spectroscopy of Isolated Molecular Ions

Abstract

Two-dimensional infrared (2D IR) spectroscopy of mass-selected, cryogenically cooled molecular ions is presented. Nonlinear response pathways, encoded in the time-domain photodissociation action response of weakly bound N2 messenger tags, were isolated using pulse shaping techniques following excitation with four collinear ultrafast IR pulses. 2D IR spectra of Re­(CO)3(CH3CN)3 + ions capture off-diagonal cross-peak bleach signals between the asymmetric and symmetric carbonyl stretching transitions. These cross peaks display intensity variations as a function of pump–probe delay time due to coherent coupling between the vibrational modes. Well-resolved 2D IR features in the congested fingerprint region of protonated caffeine (C8H10N4O2H+) are also reported. Importantly, intense cross-peak signals were observed at 3 ps waiting time, indicating that tag-loss dynamics are not competing with the measured nonlinear signals. These demonstrations pave the way for more precise studies of molecular interactions and dynamics that are not easily obtainable with current condensed-phase methodologies.

Vibrational wave-packet dynamics of the silver pentamer probed by femtosecond NeNePo spectroscopy

“…This observation of strong difference frequency band suggests the presence of coherent coupling between the ν 1 and ν 3 mode pair, yielding a relatively strong vibrational coherence from the superposition of the 1 1 , 3 1 and 0 levels, as was observed previously for trapped ions. 61–63 Excitation of the non-totally symmetric modes 5 1 and 6 1 at 26 cm −1 and 31 cm −1 , respectively, is only possible from vibrationally hot anions, in which low-frequency modes are populated at non-zero temperatures (see Fig. 3c and Fig.…”

Infrared spectra and fragmentation dynamics of isotopologue-selective mixed-ligand complexes

“…22,23 Recently, time-resolved 2D-IR spectroscopy has been applied to watch energy flow and frustrated intramolecular vibrational redistribution (IVR) in Re(CO) n (CH 3 CN) m + complexes. 24…”