LOW-TEMPERATURE ASSOCIATION KINETICS OF CF2CH2+ WITH PARENT NEUTRAL

Association rates of 1,1-difluoroethylene ions with parent neutral molecules were measured at three temperatures. Collisional (termolecular) association had a rate constant of 2.2 x 10(-23) cm(6) molecule(-2) s(-1) at 300 K, rising to 8.6 x 10(-22) at 90 K. At 140 K, radiative association and collisional association rate constants were bath determined, giving values of 1.4 x 10(-12) cm(3) molecule(-1) s(-1) and 3.2 x 10(-22) cm(6) molecule(-2) s(-1), respectively. The rate of radiative association was lower than anticipated from analogy with other hydrocarbon systems. Kinetic analysis attributed this to a surprisingly low rate of infrared photon emission, which was estimated as 5.5 s(-1). The value and the temperature dependence of the collisional association rate constant were modeled with RRKM theory, using a loose transition state and a critical energy Eo of 1.85 eV. Rescaling of literature phase space theory calculations also gave reasonable agreement with the observed temperature dependence. Considering the range of reasonable theoretical models, the best estimate of the binding energy of the dimer complex was assigned as 1.85 +/- 0.2 eV.