Vibrational Spectral Signatures and Ultrafast Dynamics of Strong H-bonds Investigated with Cryogenic Ion and 2D IR Spectroscopies

Abstract: H-bonding interactions and proton transfer processes play central roles throughout chemistry and biology. Spectroscopic studies that directly probe strong H-bonds and proton transfer reactions, however, remain a formidable experimental challenge. We aim to characterize vibrational spectral signatures and dynamics of strong H-bonds by complementing high-resolution gas-phase techniques (cryogenic ion spectroscopy) with ultrafast time-resolved solution-phase experiments (transient absorption, 2D IR). First, we report gas-phase studies on a series of proton-coupled electron transfer (PCET) model systems, which exhibit extremely broad shared H atom stretch transitions. Computational modeling reveals a unique spectral broadening mechanism arising from significant anharmonic coupling of the H atom degrees of freedom to nearly three dozen normal mode coordinates. Next, solution-phase studies investigating the intramolecular H-bond in a series of β diketones reveals surprisingly long-lived and isotope-dependent orientational dynamics. The orientational dynamics are attributed to activated H atom transfer dynamics driven by internal structural rearrangements. Finally, exciting progress on a novel experimental platform that           combines ultrafast IR spectroscopies with cryogenic ion techniques for the acquisition of multidimensional and time-resolved spectra of isolated ion ensembles will be discussed.