TIME-DEPENDENT MASS-SPECTRA AND BREAKDOWN GRAPHS .18. PYRENE

Unimolecular fragmentations of the pyrene radical cation were studied by time-resolved photo-ionization in the VUV, RRKM/QET calculations an d MS/MS with electron ionization, The major reactions observed are par allel H-. and H-2 losses, as well as consecutive H-. losses. Activatio n parameters were deduced for the reactions. Appearance energies were determined for the microsecond and millisecond time ranges, The reacti ons demonstrate large conventional and intrinsic shifts, The H-. loss reactions are characterized by loose transition states and have no rev erse activation energies, This has enabled the determination of new th ermochemical data, The C-H bond energy in the pyrene radical cation wa s deduced to be 4.6 eV and the heat of formation of the pyrenyl cation , Delta H-f0(0)(C16H9+)(C16H9+)= 1190 kJ mol(-1). The results are disc ussed in light of the possible role of pyrene-like ions in interstella r space.