THE CHEMICAL-REACTION MOLECULAR-DYNAMICS METHOD AND THE DYNAMIC TRANSITION-STATE - PROTON-TRANSFER REACTION IN THE FORMAMIDINE AND WATER SOLVENT SYSTEM

The chemical reaction mechanism in solution is analyzed by using the chemical reaction molecular dynamics (CRMD) method where a solute molecule and a few solvent molecules are regarded as a supermolecule and the chemical reaction dynamics can be analyzed in a time-dependent way on the intrasupermolecular potential surface. We have examined a proton transfer reaction, the formamidine-water system, and focused on the dynamic effect in the chemical reaction after considering the static "electronic" solvent effect. Two schemes, the constant-temperature scheme (CTS) and the constant-energy scheme (CES), have been employed, and a new type of critical state, named the dynamic transition state (DTS), was found by the appearance of a cusp in the hydrogen-bonding correlation function (HBCF). The cusp is due to the stopping of change in the O-H bond length, which produces a water molecule in the product region. In the CES, alternately modulated oscillation appeared, which is a characteristic in triatomic systems and should play an important role in energy flow in solution. It is emphasized that chemical reaction dynamics should be studied in the phase space by taking the kinetic energy or momentum into consideration.