Second-order Saddle Dynamics in Isomerization Reaction

• Published in: Regular & chaotic dynamics Vol. 26; no. 2; pp. 119 - 130
• Main Authors: Rashmi, Richa, Yadav, Komal, Lourderaj, Upakarasamy, Paranjothy, Manikandan
• Format: Journal Article
• Language: English
• Published: Moscow Pleiades Publishing 01-03-2021; Springer Nature B.V
• Subjects: Dynamical Systems and Ergodic Theory; Dynamics; Isomerization; Mathematics; Mathematics and Statistics; Potential energy; Saddle points; Time-frequency analysis; Trajectories; Wave functions; Wavelet analysis; RRKM; time-frequency analysis; wavelet transform; reaction dynamics; transition state; second-order saddle; potential energy surface
• ISSN: 1560-3547; 1560-3547; 1468-4845
• DOI: 10.1134/S1560354721020027

The role of second-order saddle in the isomerization dynamics was investigated by considering the
isomerization of guanidine. The potential energy profile for the reaction was mapped using the
ab initio
wavefunction method. The isomerization path involved a torsional motion about the imine (C-N) bond in a clockwise or an anticlockwise fashion resulting in two degenerate transition states corresponding to a barrier of 23.67 kcal/mol. An alternative energetically favorable path (
1 kcal/mol higher than the transition states) by an in-plane motion of the imine (N-H) bond via a second-order saddle point on the potential energy surface was also obtained. The dynamics of the isomerization was investigated by
ab initio
classical trajectory simulations. The trajectories reveal that isomerization happens via the transition states as well as the second-order saddle. The dynamics was found to be nonstatistical with trajectories exhibiting recrossing and the higher energy second-order saddle pathway preferred over the traditional transition state pathway. Wavelet based time-frequency analysis of internal coordinates indicate regular dynamics and existence of long-lived quasi-periodic trajectories in the phase space.