From Ultrafast Structure Determination to Steering Reactions: Mixed IR/Non‐IR Multidimensional Vibrational Spectroscopies

Abstract

Ultrafast multidimensional infrared spectroscopy is a powerful method for resolving features of molecular structure and dynamics that are difficult or impossible to address with linear spectroscopy. Augmenting the IR pulse sequences by resonant or nonresonant UV, Vis, or NIR pulses considerably extends the range of application and creates techniques with possibilities far beyond a pure multidimensional IR experiment. These include surface-specific 2D-IR spectroscopy with sub-monolayer sensitivity, ultrafast structure determination in non-equilibrium systems, triggered exchange spectroscopy to correlate reactant and product bands, exploring the interplay of electronic and nuclear degrees of freedom, investigation of interactions between Raman- and IR-active modes, imaging with chemical contrast, sub-ensemble-selective photochemistry, and even steering a reaction by selective IR excitation. We give an overview of useful mixed IR/non-IR pulse sequences, discuss their differences, and illustrate their application potential.

Vibrationally resolved electronic spectra including vibrational pre-excitation: Theory and application to VIPER spectroscopy

“…The VIPER pulse sequence as such is more complex, and includes selection of the pre-excited species by an off-resonant UV/Vis pulse and final detection by an IR probe pulse. 1,2 In our approach, which is restricted to first-order spectroscopic quantities, we cannot quantitatively calculate VIPER signals, but we are able to predict which modes are most suitable for preexcitation within the VIPER scheme.…”

“…Combined electronic-vibrational spectroscopies pave the way for new strategies of probing and controlling molecular systems. 1 This is exemplified by the recently introduced Vibrationally Promoted Electronic Resonance (VIPER) experiment 1,2 where selective infrared (IR) excitation in the electronic ground state precedes visible (VIS) excitation, as sketched in Fig. 1.…”

“…We aim to establish a general understanding of which properties favor large spectral shifts that permit effective VIPER excitation. While we do not simulate the complete VIPER pump-probe sequence 1,2 , our analysis of the vibronic spectra resulting from the combined IR-pump/VIS-pump steps, is suitable for the prediction of the relevant VIPER shifts.…”

Computational spectroscopy of complex systems

“…150 A wide range of other non-linear spectroscopic techniques is available providing insight into different sample properties. 7,14,[151][152][153][154][155][156][157][158][159][160][161] A significant effort has been invested in the efficient calculation of two-dimensional spectroscopic signals. 46,89,162,163…”

Ultrafast Vibrational Energy Transfer through the Covalent Bond and Intra- and Intermolecular Hydrogen Bonds in a Supramolecular Dimer by Two-Dimensional Infrared Spectroscopy

“…It is well known that a specific chemical group, such as CO, is an infrared-active vibrator that can be used to characterize molecular structures at the chemical bond level through its vibrational frequency and intensity observed using the conventional steady-state infrared absorption method (i.e., FTIR), which is classically known to be sensitive to chemical bonds (i.e., IR chromophores) and their structural and local solvent environment conditions. Further, molecular structural changes and associated structural dynamics, as well as the vibrational energy relaxation pathways, can be revealed by the transient nonlinear infrared method, such as pump-probe and two-dimensional infrared (2D IR) spectroscopies. − Particularly, time-dependent 2D IR spectroscopy has been used to study a number of fundamental structural and chemical phenomena of molecules, including vibrational population and anisotropic relaxations, − intramolecular vibrational energy redistribution (IVR), − intermolecular vibrational energy transfer (VET), ,− anharmonic vibrational coupling, , and equilibrium structural dynamics − including hydrogen-bonding dynamics − and structural fluctuation correlations. − Here, one of the advantages of the 2D IR method in studying these dynamical processes is that multiple IR chromophores can be utilized selectively and simultaneously in a relatively narrow-band fashion (single or double frequency) or in a broadband fashion.…”