Multiphoton Ionization/Fragmentation of SO2: Experimental and Computational Studies

The ionic fragmentation pattern of SO 2 was measured as a function of laser power atthe 223–220 nm wavelength range. The time of flight (TOF) mass spectrum showsessentially no parent ions. The principal ions observed were SO + and mass 32. Thefraction of S + ions increases monotonically with increasing laser power while thefraction of SO + which dominates at low powers reaches a maximum and falls belowthat of S + . The fraction of both ions changes nonlinearly with the laser intensity andtends to level off at the higher powers. The results are found consistent with a statistical(maximum entropy) computation of the fragmentation pattern. By comparing theobserved (S + + O 2 + )/SO + branching ratio vs. laser power with the computed branchingratio vs. energy uptake per parent molecule one obtains an energy uptake vs. laserpower curve. The results are discussed in terms of the possible dissociation/ionizationpathways.