TIME-DEPENDENT MASS-SPECTRA AND BREAKDOWN GRAPHS .16. THE METHYLNAPHTHALENES

Time-resolved photoionization efficiency (PIE) curves were measured for [C11H10]+ and [C11H9]+ for 1- and 2-methylanphthalene and for the ion-molecule reaction product [C12H11]+. PIE curves were modelled by k(E) dependences via RRKM/QET calculations based on a model by Huang and Dunbar, with a critical energy E0 = 2.41 eV and a 1000 K activation entropy DELTAS(double dagger) = - 13.3 eu. Kinetic shifts are much higher than for the analogous H. loss reaction in toluene. The crossover shift in the breakdown graphs between 24 mus and 40 ms is 1.45 eV; the conventional shift is 2.05 eV and the intrinsic shift, due to radiative decay in the infrared, is 1.1 eV. The heat of formation of [C11H9]+ is deduced to be DELTAH(f 298)(C11H9+) less-than-or-equal-to 890 +/- 20 kJ mol-1. The [C11H9]+ population contains at least 20% of methylnaphthylium, the rest being benzotropylium.