Internal temperature concept for fast-transient dynamics of chemical species in solution

Taking into consideration the recent experimental development for the fast- transient dynamics of chemical species in solution, the feasibility to intr oduce the notion of internal molecular temperature is discussed examining c omparatively several traditional temperature definitions. Then,the kinetic temperature and heat flux, which are often used in the nonequilibrium molec ular dynamics (NEMD) simulation in bulk systems, are extended, for the firs t time, to define the internal spatially "local" (ISL) kinetic temperature and heat flux for chemically reacting species in condensed phase under the ISL equilibrium assumption. The notion, internal-spatial locality (ISL) thu s introduced, is an abstract locality in the internal molecular space. For a model chemically reacting system in condensed phase, expressed by a doubl e-well potential function coupled weakly with the external bath, these time -dependent reactive flows are calculated and analyzed via the instantaneous probability density distribution obtained by solving the Fokker-Planck (PP ) equation. Further, the "intrinsic" :molecular temperature (IMT) is define d as a coordinate-integrated quantity of the ISL kinetic temperature and wa s found to show a maximum at 620 K around 100 time units. Finally, the vali dity of local equilibrium assumption (LEA) is examined by comparing the hea t flux obtained under LEA to that without LEA. It is also shown that, if on e could assume internal spatially LEA, the kinetic definition of heat flux should reasonably coincide with the expression under LEA. It is concluded t hat both concepts of the ISL temperature and IMT should propose a reasonabl e basis for understanding such a nonequilibrium and nonstationary state as the fast-transient dynamics of chemical species in solution. (C) 2000 John Wiley & Sons, Inc.