15min:

YUXIU LEI, Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104; EDWIN QUI NONES, Department of Chemistry, University of Puerto Rico, San Juan, PR 00931; AMITAVIKRAM A. DIXIT, KEON WOO LEE, PAUL L. HOUSTON, Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853.

We will present a study on the mechanism of multiphoton dissociation of the SO₂ molecule through the 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 SO₂ with a laser beam in the 222 - 234 nm region. Both SO⁺ and S⁺ fragment ions were detected but no parent SO₂⁺ appeared. The mass resolved excitation spectra (MRES) of both SO⁺ and S⁺ display the \mathrmSO₂ C ¹\mathrmB₂ X ¹\mathrmA₁ vibrational progressions. The first photon in the studied region pumps SO₂ to the C ¹\mathrmB₂ electronic state. The second photon further excites the molecule to the H Rydberg state, where it dissociates into SO + O and S + O₂ 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, \mathrmSO⁺ + h \mathrmS⁺ + \mathrmO. The internal energy distributions of the fragmentation products from dissociation of SO₂ via the H Rydberg state were also obtained using an ion-imaging spectrometer. The following five dissociation channels are observed: SO(B ^{3 -}) + O(³\mathrmP₂), SO(A³ ) + O(³\mathrmP₂) , S(¹D) + O₂(b¹ _\mathrmg), S(¹D) + O₂(a¹ _\mathrmg), and S(¹D) + O₂(X^{3 -}).