Time‐dependent mass spectra and breakdown graphs. 16–The methylnaphthalenes

Time‐resolved photoionization efficiency (PIE) curves were measured for [C 11 H 10 ] + and [C 11 H 9 ] + for 1‐ and 2‐methylnaphthalene and for the ion–molecule reaction product [C 12 H 11 ] + . PIE curves were modelled by k ( E ) dependences via RRKM/QET calculations based on a model by Huang and Dunbar, with a critical energy E 0 = 2.41 eV and a 1000 K activation entropy Δ S ‡ = −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 μs 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 [C 11 H 9 ] + is deduced to be Δ H f 298(C 11 H 9 + ) ≤ 890 ± 20 kJ mol −1 . The [C 11 H 9 ] + population contains at least 20% of methylnaphthylium, the rest being benzotropylium.