A LOW-PRESSURE STUDY OF C2N2 ION CHEMISTRY

Ion-molecule reactions of C2N2+ and C2N2 With several ions and neutrals observed or predicted to be present in the atmosphere of Titan have been examined in an ion cyclotron resonance spectrometer at room temperature and low pressures. Rate coefficients and branching ratios are reported for N+, N-2(+), HCN+, C2H2+, C2H4+, C3H5+, C4H2+, and C4H3+ With C2N2 and for C2N2+ With N-2 and C2H2. The association reaction between C2N2+ and C2N2 forming C4N4+ was examined in some detail. No evidence was found for radiative (bimolecular) association, but rapid collisional stabilization was observed. The termolecular association rate coefficient is k(3) = 1.7 x 10(-23) cm(6) s(-1)(M = C2N2), and the relative collisional stabilization efficiencies for cm the bath gases M = He, Ne, Ar, and N-2 were also measured. The mean lifetime of the (C4N4+)* complex that exhibited collisional stabilization was tau beta = 104 mu s where beta is the relative efficiency of collisional stabilization. A possible form of the C4N4+ product of association is the ion NCCNNCCN+ resulting from unrearranged addition. A mechanism is also presented showing how pressure saturation can occur when the rate coefficient for association is much less that the collision rate.