High energy vibrational excitations of nitromethane in liquid water

The pathways and timescales of vibrational energy flow in nitromethane are investigated in both gas and condensed phases using classical molecular mechanics, with a particular focus on relaxation in liquid water. We monitor the flow of excess energy deposited in vibrational modes of nitromethane into the surrounding solvent. A marked energy flux anisotropy is found when nitromethane is immersed in liquid water, with a preferential flow to those water molecules in contact to the nitro group. The factors that permit such anisotropic energy relaxation are discussed, along with the potential implications on the molecule's non-equilibrium dynamics. In addition, the energy flux analysis allows us to identify the solvent motions responsible for the uptake of solute energy, confirming the crucial role of water librations. Finally, we also show that no anisotropic vibrational energy relaxation occurs when nitromethane is surrounded by argon gas.A.J.R. acknowledges the financial support from the Departament de Recerca i Universitats de la Generalitat de Catalunya. C.C. acknowledges support from Spanish Grant No. PID2021-124297NB-C31, funded by MCIN/AEI/10.13039/501100011033 and “ERDF A way of making Europe.” E.L.S. gratefully acknowledges support from the NSF via Grant No. CHE-1900095. A.J.R. and R.R. acknowledge support from Grant No. PID2021-124297NB-C32, funded by MCIN/AEI/10.13039/501100011033 and FEDER, and from the Generalitat de Catalunya (Grant No. 2021 SGR 01411).Peer ReviewedPostprint (published version