Photodissociation Dynamics and Collision Energy Transfer of Highly Excited SO2

Abstract

As one of the simplest tri-atomic molecules, SO2 is extremely important in various fields in chemistry. SO2 is released by volcanoes and various industrial processes including combustion of sulfur containing fuel, and is well known to be the key chemical that causes the acid rain on earth. Therefore, SO2 has been studied intensively in both atmospheric chemistry as well as combustion chemistry. SO2 has also been discovered in extraterrestrial environment. For example, it is reported to be the most abundant gas observed in the atmosphere of Jupiter's moon, Io[1]. It has therefore generated great interests in the planetary chemistry as well. Even though understanding the structure, spectroscopy and reaction dynamics of SO2 has been of great and fundamental interests for more than 50 years, there are yet some very interesting topics, particularly those related to highly excited SO2, that require further investigations. In this thesis, we combine time-resolved Fourier transform infrared emission spectroscopy with theoretical modeling to study selected interesting problems relevant to highly excited SO2. First, the photodissociation of SO2 molecule by 193 nm photons is investigated. The role of different predissociation channels of electronically excited SO2 is carefully defined. Secondly, the excitation of SO2 by hot H atoms, a topic important in combustion and atmospheric chemistry, is examined. The energy transfer mechanism is identified and discussed. This newly discovered energy transfer mechanism involves the formation of the reactive intermediate species, which will greatly enhance the energy transfer efficiency on top of the classical impulsive type of collision mechanisms. In addition, the collision quenching of highly vibrationally excited SO2 with about 32,000 cm-1 energy is studied. It is found that the long range interactions contribute significantly to vibration to vibration (V-V) energy transfer. The contributions from both long range and impulsive mechanisms are discussed in detail. The studies presented in this thesis have provided important insight on the collision energy transfer and reaction dynamics of highly excited SO2 that would be useful in assessing the behavior of this important molecule in atmospheric, planetary, and combustive environments.