Vibrational dynamics of the OD stretch in an atomistic simulation of HDO in H2O

An all-atom molecular dynamics (MD) simulation of dilute HDO in H2O was used to obtain vibrational frequency spectra from the classical MD trajectories and a wavelet-based method was developed to obtain the frequency-frequency correlation functions (FFCFs) of the OD stretch vibrations. Time constants were obtained on the order of 30 fs, 150-260 fs and 3.2-3.6 ps. An OD covalent bond length correlation function was calculated and a long-timescale decay constant of 1.73 ps was obtained, similar to experimental values that range from 1.45 ps to 1.8 ps. An O-O hydrogen bond length correlation function was calculated and found to exhibit an oscillation at 150 fs and a long-timescale decay time of 3.47 ps, both in good agreement with the FFCFs. Such results suggest that the spectral diffusion observed in FFCFs can be primarily attributed to fluctuations in O-O distances. An OD stretch energy correlation function was calculated, which consists of exponential decay with a time constant of 1.13 ps. The energy correlation function also exhibits two oscillations that are indicative of resonant energy transfer processes involving the OD stretch. (C) 2022 Elsevier B.V. All rights reserved.

Automated summary

An all-atom molecular dynamics simulation was conducted to investigate the vibrational frequency spectra and frequency-frequency correlation functions of dilute HDO in H2O. The results revealed time constants for the OD stretch vibrations on the order of 30 fs, 150-260 fs, and 3.2-3.6 ps, consistent with experimental values. Additionally, resonant energy transfer processes involving the OD stretch were observed in the energy correlation function.