Time-dependent Vibrational Spectral Analysis of First Principles Trajectory of Methylamine with Wavelet Transform
The fluctuation dynamics of amine stretch frequencies, hydrogen bonds, dangling N-D bonds, and orientation profile of amine group of methylamine (MA) are investigated at ambient condition by means of dispersion corrected density functional theory based first principles molecular dynamics (FPMD) simulations. Along with the dynamical properties, various equilibrium properties such as radial distribution functions, spatial distribution function, combined radial and angular distribution functions and hydrogen bonding were also calculated. The instantaneous stretching frequencies of amine groups were obtained by wavelet transform of trajectory obtained from FPMD simulations. The frequency-structure correlation reveals that amine stretching frequency is weakly correlated with nearest nitrogen-deuterium distance. The frequency-frequency correlation function has short time scale of at around 110 fs, and a longer time scale of about 1.15 ps. It is found that, the short time scale originates from under damped motion of intact hydrogen bond of MA pairs. However, the long time scale of vibrational spectral diffusion of N-D modes are determined by the overall dynamics of hydrogen bonded as well as dangling ND groups, and the inertial rotation of amine group of the molecule.