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Articles you may be interested inPhotodissociation of (SO2XH) Van der Waals complexes and clusters (XH = C2H2, C2H4, C2H6) excited at 32 040-32090 cm−1 with formation of HSO2 and X Competitive fragmentation pathways of acetic acid dimer explored by synchrotron VUV photoionization mass spectrometry and electronic structure calculations C 2 H 2 is prepared in the 2030 0 0 0 ͑five quanta of C-H stretch͒ vibrational state and photodissociated by 243.135 nm photons that also probe the H photofragments via ͑2ϩ1͒ resonance-enhanced multiphoton ionization ͑REMPI͒ in a time-of-flight mass spectrometer. The production of H atoms is greatly enhanced upon rovibrational excitation. The REMPI action spectrum shows the characteristic features of a ⌺ u ϩ -⌺ g ϩ band and mimics the absorption spectrum, except that the R(13) line intensity is an order of magnitude higher than that expected for a Boltzmann distribution. The maximum translational energy of the H atoms obtained from dissociation of the regularly distributed rotational states is 0.67Ϯ0.10, whereas for R(13) it is 1.34Ϯ0.10 eV. The observed intensities and linewidths indicate the existence of two photodissociation pathways following the preparation of C 2 H 2 , where the C 2 H fragment is produced in two different states. In the R(13) pathway an additional bent state is prepared, or an accidental coincidence resonance is involved.