Theoretical Study of the Thermal Rate Coefficients of the H 3 + + C 2 H 4 Reaction: Dynamics Study on a Full-Dimensional Potential Energy Surface.

Ion-molecular reactions play a significant role in molecular evolution within the interstellar medium. In this study, the entrance channel reaction, H 3 + + C 2 H 4 → H 2 + C 2 H 5 + , was investigated using classical molecular dynamic (classical MD) and ring polymer molecular dynamic (RPMD) simulation techniques. We developed an analytical potential energy surface function with a permutationally invariant polynomial basis, specifically employing the monomial symmetrized approach. Our dynamic simulations reproduced the rate coefficient of 300 K for H 3 + + C 2 H 4 → H 2 + C 2 H 5 + , aligning reasonably well with the values in the kinetic database commonly utilized in astrochemistry. The thermal rate coefficients obtained using both the classical MD and RPMD techniques exhibited an increase from 100 K to 300 K as the temperature rose. Additionally, we analyzed the excess energy distribution of the C 2 H 5 + fragment with respect to temperature to investigate the indirect reaction pathway of C 2 H 5 + → H 2 + C 2 H 3 + . This result suggests that the indirect reaction pathway of C 2 H 5 + → H 2 + C 2 H 3 + holds minor significance, although the distribution highly depends on the collisional temperature.