PHOTOABSORPTION AND PHOTOIONIZATION OF PROPYNE

This work measured the absolute photoabsorption cross section of propy ne (methylacetylene, CH3CCH) in the 6-30 eV energy range. The valence- shell oscillator strength of 16.97 and the static dipole polarizabilit y of 35.82 atomic units (5.31 Angstrom(3)) were also derived from the photoabsorption spectrum by the sum-rule method. In the photoionizatio n measurement, the first ionization energy 10.369+/-0.007 eV of propyn e and appearance energies for ion fragments were determined. In additi on, new vibrational nu(9) and nu(10) progressions associated with the X E-2 ion state of propyne and Rydberg transitions converged to the A E-2 ion state were identified. In addition to the main nu(3) progressi on with the vibrational interval of 1979+/-39 cm(-1), the nu(9) and nu (10) vibrational structures of the X E-2 ion state were resolved with vibrational frequencies of 586+/-74 cm(-1) and 289 +/- 65 cm(-1), resp ectively. Moreover, the absolute branching ratios, photoionization qua ntum yield, and partial photoionization cross sections for C3H4+, C3H2 +, and C3H+ production in the 10.3-21.4 eV region were determined. Fou r shape resonance states were tentatively assigned at 11.2, 12.7, 14.8 and 15.8, and 16.7 eV. Furthermore, a CD3CCH isotopic measurement was taken to examine the reaction pathways of I-I-dissociative photoioniz ation of propyne. According to the evolution of the C3D3+/C3D2H+ ratio , plausible decay mechanisms for H-dissociative photoionization of pro pyne were proposed. (C) 1998 American Institute of Physics.