TIME-RESOLVED DISSOCIATION OF BROMONAPHTHALENE ION STUDIED BY TPIMS AND TRPD - HEAT OF FORMATION OF NAPHTHYL ION

Dissociation of 1-bromonaphthalene and 2-bromonaphthalene molecular io ns was studied by time-resolved photodissociation (TRPD) in the ion cy clotron resonance spectrometer at ultraviolet wavelengths and by time- resolved photoionization mass spectrometry (TPIMS) in the vacuum ultra violet. TRPD of the 1-bromonaphthalene ion gave rate constants of 3.4 X 10(3) s-1 at 266 nm (4.93 eV ion internal energy) and 1.6 X 10(4) s- 1 at 252 nm (5.19 eV internal energy). The TRPD results, and the time- resolved PIE curves for the parent, C10H7Br+, and the daughter, C10H7, were modeled by RRKM calculations. The critical energies and 1000 K activation entropies obtained were E(o) = 3.23 +/- 0.07 eV and DELTAS( double dagger)1000K = 7.7 +/- 2.5 eu for 1-bromonaphthalene and E(o) = 3.08 +/- 0.07 eV and DELTAS(double dagger)1000K = 5.2 +/- 1.2 eu for 2-bromonaphthalene. The reactions demonstrate loose transition states characteristic of simple bond cleavages. Kinetic shifts are much highe r than for the analogous Br. loss reaction in the bromobenzene ion. Th e conventional kinetic shift is 1.6 eV and the intrinsic shift, due to infrared radiative decay, is 1.1 cV. The heat of formation of the alp ha-naphthyl cation is deduced to be DELTAH-degrees f,0(C10H7+) = 281 /- 3 kcal/mol. The correlation between bond energies for benzene and n aphthalene derivatives is discussed.