Sonochemical reaction of water under various noble gases, such as Xe, Kr, Ar, and He, has been investigated by the determination of decomposition products. In Xe-, Kr- and Arsaturated solution, decomposition products of water, H_2, H_2O?2 and O_2, are observed while in He-saturated solution, H_2O_2 is observed but H_2 and O_2 are not. It is considered that more effective chemical reaction is derived during the collapse of cavitation bubbles containing noble gases of lower thermal conductivity and higher solubility in water. The yield of decomposition products is highest under Xe, which has the lowest thermal conductivity and highest solubility in water. In the cases of sonolysis of t-BuOH, the pyrolysis temperatures within the cavitation bubble are estimated from the product ratio of ethylene plus acetylene to ethane. The yields of decomposition product, methane, ethane, ethylene, and acetylene, are increased in order Xe > Ar > He, while the temperatures estimated from the product ratio under He, Ar and Xe are almost same in the range from about 3400 to 3900K. It is supposed that the acceleration of sonochemical reaction to vary dissolved gases is responsible for the gaseous characteristics of solubility in water. The number of cavitation bubbles is increased with increasing solubility. As a result, the reaction sites are increased. It is reported that the rapid compression of gas during cavitational collapse leads to nearly adiabatic heating of the contents of the bubble because thermal transport is slower than the collapse.
