Short-time Fourier transform analysis of ab initio molecular dynamics simulation: collision reaction between CN and C4H6

Collision reactions between cyano radical (CN) and dimethylacetylene (C4H6) are thought to occur in the atmosphere of Saturn's moon Titan. However, it is difficult to reproduce reactions occurring in unique environments to study their dynamical processes. In this study, collision reactions between CN and C4H6 were investigated using ab initio molecular dynamics (AIMD) simulations. The simulation results were categorized into three kinds: nonreactive collision, incorporation, and substitution. Short-time Fourier transform analysis of velocity autocorrelation functions obtained by the AIMD simulations, which has been recently developed by our research group, was performed to examine the nonequilibrium condition of the vibrational states. Spectrograms, which correspond to the time evolution of power spectra, clarify the relationship between the three reaction channels and the dynamical changes of the vibrational states.