Spectroscopic measurements of Si-O recombination process in laser-induced quartz vapor plumes
© The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS); The Seismological Society of Japan; The Volcanological Society of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sciences. 2007
Received: 20 September 2003
Accepted: 16 January 2007
Published: 8 June 2007
The thermal dissociation of SiO2 in impact-induced vapor is very important because it controls the redox state of the vapor. However, the thermal dissociation of SiO2 and its recombination are not well understood. The present study investigates experimentally the kinetics of the Si-O recombination process at high temperatures. Laser-induced quartz vapor is observed by means of time-resolved spectroscopy, and the atomic lines of Si and molecular bands of SiO are measured in order to estimate the temperature and the column densities of Si and SiO. The results of these experiments show that Si and O recombine as the vapor cools from 5000 to 3000 K. A comparison of the observed chemical composition and equilibrium calculations suggests that the recombination reaction between Si and O proceeds rather efficiently under a condition that differs significantly from the thermo-chemical equilibrium. This result is explained well if the rate constant of the Si-O recombination process does not depend strongly on the temperature; the activation energy is very small. These results suggest that the Si-O recombination process may not be approximated by a frequently-used ‘freeze-out’ model.