Spectroscopy and dynamics of highly excited sulfur dioxide

The dynamics and spectroscopy of SO₂ in its Rydberg states and its highly vibrationally excited level of ground electronic state have been investigated. The dynamics and structure of SO₂(C˜)-Ar complex have also been studied. These investigations have involved the use of different laser detection techniques. Furthermore, because of understanding the role of phase in the light-molecule interaction, we have developed an unique way to demonstrate the manipulation of coherence in REMPI of SO ₂.; First, The triplet g˜ Rydberg state of the SO ₂ molecule has been studied by accessing the triplet-manifold, using two-color REMPI spectroscopy. The Rydberg G˜ state is assigned correctly to 4p through this study. The dynamics information are also extracted from the broadened ro-vibrational spectra and the change of the fragmentation pattern in the (1+2+1) and (2+1+1) ionization pathways. This provides a direct measure of the dissociation rate in the energy region of $\sim$52300 cm−1 (191 nm), which is on the order of 0.55 ps. Second, the measured collisional rate constant of a single, highly excited vibrational level SO₂ (X˜) at 44877.52 cm −1 is 3.5 × 107 Torr−1sec −1, based on the analysis of the fluorescence quantum beat resulting from the strong coupling of the C˜ and X˜ states. This value gives an effective distance for relaxation collisions of 8.3 Å, which is twice larger than the one defined by the van der Waals radii! Third, taking advantage of intramolecular phase created by coherent excitation of the C˜ ← X˜ ′ $110220300$, qR(6)_1,5 transition of SO ₂, we are able to manipulate of the ionization products from the C˜ state and the X˜ state through intermediate Rydberg states by the time-resolved two-color multiphoton ionization technique. With the wavelength of the probe laser at 229.17 nm and 220.75 nm, the ionization products are predominantly from the X˜ state and the C˜ state, respectively. This method has provided a new way to control of chemical reactions. Finally, fluorescence excitation spectra of SO₂-Ar generated in a supersonic expansion near the SO₂ C˜ ← X˜ $000,210$, and $320$ bands have been obtained. The structure of SO₂-Ar is determined, the electronic relaxation in the origin of SO₂(C˜)-Ar is examined.