- Research Field -
A. Miyoshi

Our Research Field

Chemical Kinetics

  Our research field is called Chemical Kinetics of free radicals.   For example, the catalytic behavior of the following ozone destruction reaction by chlorine atoms [1] (See the page of Free Radicals, for details), that one chlorine atom desroys 104 ozone molecules, cannot be explained either by the net reaction nor by the reaction (1) or (2) only.
Cl + O3 → ClO + O2   (1)
ClO + O → Cl + O2   (2)
O + O3 → 2 O2   (net reaction)
The purpose of our research is to elucidate what reactions [reactions (1) and (2) in the example shown above] are involved in the target phenomenon [the ozone destruction, here].   Obviously, for the atmospheric environmental problems, the accurate understanding of the phenomena is required to discuss the countermeasures.
  Also, the knowledge on the chemical kinetics of the combustion is inevitable for the development of highly efficient and low-emission combustion technologies and assessment of the combustion or explosion safely.   Below are the three major elementary reactions involved in the high-temperature combustion of hydrogen, which is the chamically simplest fuel.
H + O2 → OH + O   (3)
O + H2 → OH + H   (4)
OH + H2 → H2O + H   (5)
2H2 + O2 → H2O + H + OH   (net reaction??)
Contrary to the ozone destruction chain reaction, for which the chain carriers (chemical species that carry the chain reaction; Cl and ClO for the ozone destruction) disappear in the net reaction since their consumption and production is in balance, chain carriers (H, O, and OH) always remains in the right hand side of the net reaction irrespective of the ways of the summation for this chain reaction system of hydrogen.   This is because the reactions (3) or (4) produces two chain carriers from one chain carrier.   Such a chain reaction system is called branching chain reaction system, and it describes the essense of the explosive nature of the mixture of fuel such as hydrogen and oxygen (or air) that it results in the explosion with a small triggering by self-multiplication of the chain carriers.   For the combusion of hydrogen, it is possible to describe the combsution and explotion phenomena with totally 20 elementary steps includeing the three shown above.   However, for hydrocarbon molecules with large number of carbons, a huge number of elementary steps are necessary to describe the combustion phenomena; for example, to describe the combustion of heptane (C7H16), thousands of elementary reactions are needed.   The goal of one of our research projects is the construction of reliable reaction mechanisms for such huge reaction systems, via the development of a software tool which automatically estimates the reaction mechanisms and technique to find systematic change of the rate coefficients by the quantum chemical calculations.

[1]  M. J. Molina and F. S. Rowland, Nature, 249, 810 (1974).

Current Research Subjects

 A few of our current research subjects are introduced below.

Chemical Kinetics of Particulate Matters (Soot) Formation from Combustion

  The reduction of the particulate matter (soot) and polycyclic aromatic hydrocarbons (PAH) emitted from the internal combustion engines is one of the important missions for the combustion technology.   However, the chemical process of soot formation is very complicated, and our knowledge on it is far from the predictable modeling and thus the development of combustion technology still relies largely on the empirical knowledge.   Experimental measurements and quantum chemical calculations for key reactions are under way and our final goal is to establish a reliable chemical reaction model.

Low-Temperature Oxidation Mechanism of Hydrocarbons

  The dominant combustion oxidation process of hydrocarbon below about 900 K is called 'low-temperature oxidation process,' which is important to understand the ignition phenomena of fuel/air mixtures.   The knowledge on the process is required since it controls the 'knocking' in spark ignition engines, as well as to control and understand the HCCI combustion.   Our main purpose is to understand the mechanism of the reactions in the process, which include complex isomerization reactions of radicals by experimantal direct investigations of hydrocarbon radicals and peroxy radicals and quantum chemical calculations.

Construction of the Mechanism for New-Types of Oxidants

  Although, in recent semiconductor industry, use of the new types of oxidant gases (NF3, ClF3, ClF5, etc.) for etching and cleaning are increasing, the combustion safety regulations for this gases when they are made contact with hydrocarbons have not been well standarized.   We are constructing the reaction mechanisms for these new types of oxidant with hydrocarbons by using the quantum chemical calculations.