The vibrational energy relaxation dynamics of the excited free OH bond on the ice surface are investigated using ab initio molecular dynamics (AIMD) simulations. The present AIMD study reproduces experimental results obtained via pump-probe sum-frequency generation spectroscopy. Simulations were conducted at 100 and 200 K for ice surfaces and compared with previous results at 300 K for water surfaces. The relaxation mechanisms were analyzed by selectively constraining specific vibrational modes, revealing distinct pathways: intramolecular stretch coupling, bend coupling, and intermolecular stretch coupling via reorientation or dipole-dipole interactions. At higher temperatures, intramolecular stretch coupling dominates, while at lower temperatures, the reorientation of the free OH is restricted; alternatively, intermolecular dipole-dipole coupling becomes more significant due to the vibrational delocalization of ice. For isotopically diluted systems (HOD in D2O), relaxation occurs primarily through stretch-bend combination coupling.
Tatsuya Ishiyama (Sat,) studied this question.