PHOTODISSOCIATION OF ROVIBRATIONALLY EXCITED C2H2 - OBSERVATION OF 2 PATHWAYS

C2H2 is prepared in the 2030(0)0(0) (five quanta of C-H stretch) vibra tional state and photodissociated by 243.135 nm photons that also prob e the H photofragments via (2+1) resonance-enhanced multiphoton ioniza tion (REMPI) in a time-of-flight mass spectrometer. The production of H atoms is greatly enhanced upon rovibrational excitation. The REMPI a ction spectrum shows the characteristic features of a Sigma(u)(+)-Sigm a(g)(+) 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 a toms obtained from dissociation of the regularly distributed rotationa l states is 0.67+/-0.10, whereas for R(13) it is 1.34+/-0.10 eV. The o bserved intensities and linewidths indicate the existence of two photo dissociation pathways following the preparation oi C2H2, where the C H fragment is produced in two different states. In the R(13) pathway an additional bent state is prepared, or an accidental coincidence reson ance is involved. (C) 1997 American Institute of Physics.