Electric Field Effects on Amine Regeneration in Post-Combustion Carbon Capture—Part II: Mode-Selective Infrared Laser Excitation Probed by Nonequilibrium Ehrenfest Electron-Nuclear Dynamics

Amine regeneration is the most energy-intensive step in amine-based post-combustion carbon capture (PCCC), and reducing its energy demand is essential for improving the overall efficiency of the capture process. In Part I of this series, static electric fields were shown to stabilize CO2 absorption products and increase the energy requirements for amine regeneration. In Part II, we investigate whether the fundamentally different response to time-dependent infrared laser excitation could provide molecular mechanisms for reducing the energy demand of amine regeneration. Nonequilibrium Ehrenfest electron–nuclear dynamics simulations were performed for aqueous zwitterion, carbamate, and bicarbonate systems representative of CO2 capture by monoethanolamine (MEA) and triethanolamine (TEA), using a benchmarked density functional tight-binding framework. Pulsed and continuous-wave infrared laser excitation was applied at frequencies corresponding to selected molecular vibrational modes. Laser-induced heating was strongly mode selective, with the CCO2–OCO2–CCO2 bending mode consistently producing the largest overall temperature increase across all three systems. However, the modes producing the strongest total-system heating were not necessarily those that preferentially deposited vibrational kinetic energy into the CO2–amine species rather than the surrounding water. Preferential energy deposition was strongly system dependent, being greatest for the symmetric CCO2–OCO2 stretch in the zwitterion, the CCO2–NMEA stretch in the carbamate, and the CCO2–OOH stretch in the bicarbonate. Infrared laser excitation also produced pronounced mode-dependent structural and energetic perturbations of the regeneration-relevant CCO2–NMEA and CCO2–OOH bonds, including increases in their mean lengths and energies, broadening of their bond-length and bond-energy distributions, and increased probabilities of sampling transient elongated-bond configurations. Importantly, the strongest bond perturbations did not always result from direct excitation of the monitored bond, consistent with vibrational coupling and energy redistribution. These results identify three complementary effects that may contribute to infrared-assisted amine regeneration: efficient total-system heating, preferential energy deposition into the CO2–amine species, and mode-selective structural and energetic perturbations of bonds involved in CO2 retention. Because no single vibrational mode maximizes all three effects across the investigated systems, selecting an excitation frequency is inherently a multi-objective problem. The findings provide a molecular-level basis for investigating infrared-assisted regeneration strategies, although their potential to reduce process-level energy consumption remains to be established.