Correlations of intra- and intermolecular dynamics and structure in liquid para-hydrogen

Abstract

Although hydrogen is the simplest of all molecular species, its nuclear quantum effects dominate the structure and thermodynamical properties of the condensed phases. With a recently developed nonempirical quantum molecular dynamics simulation method, we present intuitive understandings of real-time dynamics of each para-hydrogen(p−H[2]) molecule in the liquid phase including its H-H bond vibrations, molecular orientations, and librational motions. The short- and long-living memories of angular dynamics we found suggest that p−H[2] should be described as a librating nonspherical diatomic molecule and can be characterized by two typical dynamics: kinetic motions inside a solvation shell and diffusive dynamics out of the shell. The real-time trajectory reveals that structural rearrangements of a p−H[2] molecule such as breakout from a solvation shell significantly correlate with its intramolecular structure and fluctuations. The H-H bond power spectra completely fitted by two functions also indicate that liquid p−H[2] has two typical structures. The condensed-phase effects on shifts and broadening of H-H bond stretching frequencies, intrinsic librational dynamics, and molecular orientational distributions are computationally demonstrated and physically rationalized.