Universidade do Algarve, FCT, DQF, and CIQA, P8005-139 Faro, Portugal.
We studied photodecomposition dynamics of (SO2⋯XH) Van der Waals' (VdW) complexes and clusters in gas phase, with X = C2H, C2H3, and C2H5. SO2 was excited by frequency-doubled radiation of a tunable dye laser and resonance-enhanced multiphoton ionization was used to detect the C2H (m/z 25), C2H3 (m/z 27), and C2H5 (m/z 29) ions by time-of-flight mass spectroscopy. Spectra obtained at higher nozzle pressures (P0 > 2.5 atm) indicate formation of clusters. Detailed studies of the VdW complex structure were carried out by analyzing the rotational structure of the respective action spectra. We also performed ab initio theoretical analysis of structures of the VdW complexes and transitional states leading to photodecomposition. We find that the structure of the transition state is significantly different as compared to the equilibrium ground-state structure of the respective complex. The photodecomposition mechanism depends on the hydrocarbon molecule bound to SO2.