Energy relaxation path of excited free hydrogen oxide vibrational energy at the air/water interface
Energy relaxation path of excited free hydrogen oxide vibrational energy at the air/water interface lead image
Energy relaxation of a locally excited water molecule is a ubiquitous physical phenomenon on earth. The relaxation path at the air/water interface provides researchers with key information to understand chemical reaction dynamics at aqueous surfaces related to various atmospheric and biological chemical reactions.
Tatsuya Ishiyama explains how the completely different relaxation paths between the surfaces of pure water and isotopically treated water can produce the similar relaxation rates.
“The fact that the relaxation time scales of free OH at the surface of pure water and isotopically diluted water are very similar to each other is surprising, because the vibrational couplings of H2O and HOD in D2O are usually considered to be quite different from each other,” said Ishiyama.
The study used a first principle molecular dynamics (AIMD) simulation, which reproduced the experimental relaxation time scales of the excited free OH vibration at both surfaces. The simulation also revealed detailed relaxation paths of excess free OH vibrational energy.
This work introduced a constrained method for the bond and angles of the water molecules relevant to specific vibrational modes in the AIMD simulations to determine the relaxation rate of each complex relaxation path uniquely.
This methodology was particularly important for assessing the relaxation paths at an air/water interface, which is in a heterogeneous environment that is difficult to be treated by a previous method based on perturbation theory.
“The present methodologies can be applied for any other vibrationally excited molecular systems observed in the pump-probe spectroscopy to elucidate those relaxations paths,” said Ishiyama.
Source: “Energy relaxation path of excited free OH vibration at an air/water interface revealed by nonequilibrium Ab initio molecular dynamics simulation,” by Tatsuya Ishiyama, Journal of Chemical Physics (2021). The article can be accessed at https://doi.org/10.1063/5.0038709 .
