MECHANISM OF THE MULTIPHOTON DISSOCIATION OF $SO_{2}$ VIA THE $\tilde{H}$ RYDBERG STATE

Abstract

We will present a study on the mechanism of multiphoton dissociation of the $SO_{2}$ molecule through the $\tilde{H}$ Rydberg state. For this study, a homemade Wiley-McLaren linear time-of-flight (TOF) spectrometer was constructed to characterize the fragments produced during irradiation of $SO_{2}$ with a laser beam in the $222 - 234$ nm region. Both $SO^{+}$ and $S^{+}$ fragment ions were detected but no parent $SO^{+}{2}$ appeared. The mass resolved excitation spectra (MRES) of both $SO^{+}$ and $S^{+}$ display the $SO{2} \tilde{C} B_{2} \leftarrow X^{1}A_{1}$ vibrational progressions. The first photon in the studied region pumps $SO_{2}$ to the $\tilde{C}^{1}B_{2}$ electronic state. The second photon further excites the molecule to the $\tilde{H}$ Rydberg state, where it dissociates into $SO + O$ and $S + O_{2}$ fragments. The third photon then ionizes the SO fragment. From the power dependence of the ion intensity and a kinetic model we developed, we conclude that $S^{+}$ is produced by a one-photon dissociation, $SO^{+} + h\nu \rightarrow S^{+} + O$. The internal energy distributions of the fragmentation products from dissociation of $SO_{2}$ via the $\tilde{H}$ Rydberg state were also obtained using an ion-imaging spectrometer. The following five dissociation channels are observed: $SO(B^{3}\Sigma^{-}) + O(^{3}P_{2}),SO(A^{3}\Pi) + O(^{3}P_{2})$, $S(^{1}D) + O_{2}(b^{1}\Sigma_{g}),S(^{1}D) + O_{2}(a^{1}\Delta_{g})$, and $S(^{1}D) + O_{2}(X^{3}\Sigma^{-})$.