Multiphoton Ionization/Fragmentation of SO₂: Experimental and Computational Studies

Abstract

The ionic fragmentation pattern of SO₂ was measured as a function of laser power at the 223–220 nm wavelength range. The time of flight (TOF) mass spectrum shows essentially no parent ions. The principal ions observed were SO⁺ and mass 32. The fraction of S⁺ ions increases monotonically with increasing laser power while the fraction of SO⁺ which dominates at low powers reaches a maximum and falls below that of S⁺. The fraction of both ions changes nonlinearly with the laser intensity and tends to level off at the higher powers. The results are found consistent with a statistical (maximum entropy) computation of the fragmentation pattern. By comparing the observed (S⁺ + O2+)/SO⁺ branching ratio vs. laser power with the computed branching ratio vs. energy uptake per parent molecule one obtains an energy uptake vs. laser power curve. The results are discussed in terms of the possible dissociation/ionization pathways.