We present a first principles molecular dynamics study of vibrational spectral diffusion andhydrogen bond dynamics in deuterated ammonia without using any empirical potential atambient and supercritical region. The calculations are based on ab initio molecular dynam-ics simulations for the generation of trajectories and for frequency calculations, time seriesanalysis is employed by using wavelet method. In ammonia although one-to-one relationdoes not exist between the instantaneous frequency of an ND bond and the distance ofits associated hydrogen bond but this relation hold on average. By frequency-time corre-lation and spectral hole dynamics calculations, the dynamics of the spectral diffusion hasbeen investigated at molecular level. We have also used the dispersion correction functional(BLYP-D) proposed by Grimme in our simulations and compared it with our results havingno dispersion corrections (BLYP) for both ambient as well as for supercritical ammonia.The details of the time constants of frequency correlations and spectral shifts are found tobe depend on the frequencies of chosen ND bonds and are analyzed in terms of the dynamicsof hydrogen bonds of varying strengths and also for free non-hydrogen bonded ND groups.In supercritical ammonia, there exists interplay between the dynamics of hydrogen bonds,dangling ND groups, and the inertial rotation of the ND bonds that determines the timescales of spectral diffusion in a subtle manner.

Weak, weaker, weakest ammonia: journey from ambient to supercritical region

247th National Meeting (2014)

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