Coherent Fifth-Order Visible–Infrared Spectroscopies: Ultrafast Nonequilibrium Vibrational Dynamics in Solution

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 116; no. 26; pp. 7023 - 7032
• Main Authors: Lynch, Michael S, Slenkamp, Karla M, Cheng, Mark, Khalil, Munira
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 05.07.2012
• Subjects: Coherence; Couplings; Dispersion; Dynamics; Electronics; Nonlinear dynamics; Spectroscopy; Time
• DOI: 10.1021/jp303701b
• ISSN: 1089-5639

Obtaining a detailed description of photochemical reactions in solution requires measuring time-evolving structural dynamics of transient chemical species on ultrafast time scales. Time-resolved vibrational spectroscopies are sensitive probes of molecular structure and dynamics in solution. In this work, we develop doubly resonant fifth-order nonlinear visible–infrared spectroscopies to probe nonequilibrium vibrational dynamics among coupled high-frequency vibrations during an ultrafast charge transfer process using a heterodyne detection scheme. The method enables the simultaneous collection of third- and fifth-order signals, which respectively measure vibrational dynamics occurring on electronic ground and excited states on a femtosecond time scale. Our data collection and analysis strategy allows transient dispersed vibrational echo (t-DVE) and dispersed pump–probe (t-DPP) spectra to be extracted as a function of electronic and vibrational population periods with high signal-to-noise ratio (S/N > 25). We discuss how fifth-order experiments can measure (i) time-dependent anharmonic vibrational couplings, (ii) nonequilibrium frequency–frequency correlation functions, (iii) incoherent and coherent vibrational relaxation and transfer dynamics, and (iv) coherent vibrational and electronic (vibronic) coupling as a function of a photochemical reaction.