Evaluation of the Lifetime of Gaseous Ion-Neutral Complexes. 1. A Chemical Activation Study
Massimiliano Aschi, Marina
Attina', Fulvio Cacace,* and Giuseppe D'Arcangelo
Contribution
from the Universita' di Roma "La Sapienza", Piazzale Aldo
Mora 5, I-00185, and Universita' di Roma "Tor Vergata",
V.le della Ricerca Scientifica 00133, Rome, Italy
Abstract:
The lifetime of typical ion-neutral complexes (INC) has been evaluated by a chemical activation approach whereby gaseous INC are formed by an exothermic process that imparts them excess internal energy, raising their temperature to T0, well above the temperature (T) of the bath gas. The hot INC can undergo either prompt reaction at T0 or thermal reaction at T following collisional deactivation, and the branching ratio of the two processes is deduced from the composition of the products. We have investigated aromatic tert-butylation promoted by addition of toluenium ions to RX neutrals (R = t-C4H9, X = Cl, OH), a reaction that displays a marked temperature dependence of the isomeric composition of the products and, in addition, is known to occur within genuine INC. Following a preliminary study by Fourier transform ion cyclotron resonance and triple quadrupole mass spectrometry, the pressure dependence of the meta/para ratio of the tert-butyltoluenes formed has been investigated by the radiolytic technique in the range from 50 to 4560 Torr in CH4, CH3F and C3H8 at temperatures from 0 to 42 C.