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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Vibrational Spectral Diffusion in Supercritical D2O from First Principles:An Interplay between the Dynamics of Hydrogen Bonds,Dangling OD Groups,and Inertial Rotation
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Vibrational Spectral Diffusion in Supercritical D2O from First Principles:An Interplay between the Dynamics of Hydrogen Bonds,Dangling OD Groups,and Inertial Rotation

机译：从第一原理到超临界D2O的振动光谱扩散：氢键动力学，悬空OD群和惯性旋转之间的相互作用

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We have presented a first principles theoretical study of vibrational spectral diffusion and underlying molecular dynamics in supercritical heavy water at three different densities ranging from 1.1 to 0.39 g cm~(-3).Our calculations are based on ab initio molecular dynamics simulations for trajectory generation and wavelet analysis for frequency calculations,and no empirical potential parameters are involved in the present study.Calculations of OD frequency-distance(D…O)conditional probabilities reveal that the rate of increase of OD frequency with D…O distance gradually decreases with lowering of density.Also,the maximum probability moves to a higher frequency-larger D…O distance region with decreasing density due to weakening of hydrogen bonds and increased number of dangling OD bonds in these systems.The correlations between the stretch frequencies and the electric fields on D atoms(along OD bonds)are also calculated,and the magnitude of such correlations is found to be similar to those of frequency-distance(D…O)correlations for the present supercritical systems.The vibrational spectral diffusion in supercritical water shows two time scales:one around 100 fs or less and the other in the region of 150-600 fs with the shorter time scale carrying the larger weight.It is found that,unlike ambient water,for supercritical water the slower component of the spectral diffusion does not necessarily capture the hydrogen bond dynamics at all densities.Rather,an interplay between the dynamics of hydrogen bonds,dangling OD groups,and the inertial rotation of OD bonds determines the times scales of spectral diffusion in a rather subtle manner.While the slower component of spectral diffusion at high density is determined by the lifetimes of hydrogen bonds,it is the lifetime of dangling OD groups that decides the slower component at low density,and the reverse holds for the faster components.The fast inertial rotation also shows up as the faster component of spectral diffusion.Dynamical correlations between the relaxation of frequency fluctuations and that of electric field fluctuations are also explored.Our calculations of rotational dynamics show,unlike ambient water,no frequency dependence of the rotational relaxation of OD bonds because of faster interconversion of different hydrogen bonding states and a reduced role of the hydrogen bond strength as a significant determinant of rotational motion caused by higher thermal energy of supercritical states.
机译：我们已经提出了从1.1到0.39 g cm〜（-3）的三种不同密度下的超临界重水中振动光谱扩散和潜在分子动力学的第一原理理论研究。我们的计算基于从头算分子动力学模拟来产生轨迹OD频率距离（D…O）条件概率的计算表明，OD频率随D…O距离的增加率随着降低而逐渐减小。此外，由于这些系统中氢键的弱化和悬空的OD键数量的增加，最大的概率随着密度的减小而移动到了更高的频率更大的D…O距离区域。拉伸频率与电场之间的相关性还计算了D原子上的OD键（以及OD键）的相关性，其大小与t相似。对于当前的超临界系统，其频率-距离（D…O）相关性的软管。在超临界水中的振动频谱扩散表现出两个时间尺度：一个约为100 fs或更小，另一个约为150-600 fs且时间更短。研究发现，与环境水不同，对于超临界水，光谱扩散的较慢成分并不一定能在所有密度下都能捕捉到氢键动力学。相反，氢键动力学之间存在相互作用，使OD悬空。 OD键的惯性旋转以相当微妙的方式确定了光谱扩散的时间尺度。虽然高密度下光谱扩散的较慢成分取决于氢键的寿命，但悬挂的OD基团的寿命决定了决定低密度下较慢的分量，反之则代表较快的分量。快速惯性旋转也表现为光谱扩散的更快分量。我们还研究了频率波动的弛豫与电场波动之间的数学相关性。我们对旋转动力学的计算表明，与环境水不同，OD键旋转弛豫与频率没有关系，因为不同氢键态的快速相互转换和氢键强度作为由超临界态的较高热能引起的旋转运动的重要决定因素的作用降低。

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