Theoretical exploration of astrochemical reactions: Leveraging ringpolymer molecular dynamics and machine-learning techniques
Murakami, T.,1,2* Takayanagi, T.112murakamit@mail.saitama-u.ac.jp, Saitama University, JapanSophia University, Japan

We have embarked on the research project entitled “Next Generation Astrochemistry”. Our
mission is to comprehend reaction mechanisms1-7 and furnish reliable thermal rate coefficientsto enhance the precision of the rate coefficients in the astrochemical database.
To understand chemical reactions, a potential energy surface spanning the 3N-6 dimensions,where N represents the number of atoms, is necessary. We have recently developed several fulldimensional potential energy surfaces (PESs) such as H- + C2H2 ® H2 + C2H-, NH3+ H2 ®
NH4+ + H, and (HCOOH)H+ ® CO + H3O+ / HCO+ + H2O reactions1-3. To develop these PESs,
we employed a machine-learning technique, utilizing polynomial fitting from preliminary
dynamics data and potential energies at various intrinsic reaction coordinates.4
In the cold environments typical of the interstellar medium, nuclear quantum effects canprofoundly impact chemical dynamics. Hence, we employed the ring-polymer moleculardynamics (RPMD) simulation method. Our investigations have revealed that nuclear quantum
effects and the quantum fluctuation of nuclei play a crucial role not only in the aforementioned
collision reactions1-3 but also in determining the H2 sticking probability on ice clusters.5
In this presentation, we will introduce our recent research on the branching dynamics of H3+ +C2H4 ® H2+ C2H5+ / 2H2+ C2H3+ and H3+ + HNCO ® H2+ HNCOH+ / H2+ H2NCO+ reactions.
Additionally, we delve into the transition state dynamics of CH3OH + OH• ® CH3O• + H2O
with the goal of comprehending the intricate reaction mechanism post-transition state from a
dynamical viewpoint, a perspective unattainable through the statistical transition state theory.
1

Murakami, T.; Iida, R.; Hashimoto, Y.; Takahashi, Y.; Takahashi. S.; Takayanagi. T. Ring-Polymer Molecular
Dynamics and Kinetics for the H- + C2H2 ® H2 + C2H- Reaction Using the Full-Dimensional Potential Energy
Surface. J. Phys. Chem. A 2022, 126, 9244-9258.
2Hashimoto, Y.; Takayanagi. T.; Murakami T. Theoretical Calculations of the Thermal Rate Coefficients for theInterstellar NH3+ H2 ® NH4+ + H Reaction on a New Δ-Machine Learning Potential Energy Surface. ACS EarthSpace Chem. 2023, 7, 623-631.
3
Murakami, T.; Ibuki, S.; Hashimoto, Y.; Kikuma, Y.; Takayanagi. T. Dynamics study of the post-transitionstate-bifurcation process of the (HCOOH)H+ ® CO + H3O+ / HCO+ + H2O dissociation: Application ofmachine-learning techniques. Phys. Chem. Chem. Phys. 2023, 25, 14016-14027.
4Takayanagi. T. Application of Reaction Path Search Calculations to Potential Energy Surface Fits. J. Phys.
Chem. A 2021, 125, 3994-4002.
5
Murakami, T.; Ogino, K.; Hashimoto, Y.; Takayanagi. T. Ring-polymer Molecular Dynamics Simulation for
the Adsorption of H2 on Ice Clusters (H2O)n (n=8, 10, and 12). ChemPhysChem. 2023, 24, e202200939.
6
Murakami, T.; Takayanagi. T. Interstellar Benzene Formation Mechanisms via Acetylene Cyclotrimerization
Catalyzed by Fe+ Attached to Water Ice Clusters: Quantum Chemical Calculation Study. Molecules. 2022, 27,7767.
7
Murakami, T.; Matsumoto, N.; Fujihara, T.; Takayanagi. T. Possible Roles of Transition Metal Cations in theFormation of Interstellar Benzene via Catalytic Acetylene Cyclotrimerization. Molecules. 2023, 28, 7454.