REACTIONS OF ATMOSPHERIC IONS WITH SELECTED HYDROFLUOROCARBONS

Selected atmospheric ions have been studied for reactivity with the hy drofluorocarbons (HFC's) CF3CH2F, CF3CHFCF3, and CF3CHFCHF2 and with C HBrF2; the reactant ions chosen for study are O+, O-2(+), O-, O-2(-), H3O+, H3O+. H2O, H3O+.(H3O)(2), NO3-, and NO3-. HNO3. Rate constants a nd product branching fractions for these ion-molecule reactions were m easured using a selected ion flow tube (SIFT) instrument operated at 3 00 K. The ions O+ and O- reacted at the collisional rates, forming a n umber of ionic products in most cases. Most of the other reactions stu died were found to be inefficient. The ions H3O+ and NO3- reacted inef ficiently by association in all cases. The solvated ions H3O+. H2O, H3 O+.(H2O)(2), and NO3-. HNO3, which are representative of the abundant ionic species in the lower atmosphere, were unreactive with the compou nds investigated; we conclude from this that atmospheric ion chemistry is not a significant sink for these HFC's. The observation of proton transfer from CF3CHFCF3 and CF3CHFCHF2 to O- allows a lower bound to t he gas-phase acidities of these HFC's to be assigned: Delta H-acid(CF3 CHFCF3) and Delta H-acid(CF3CHFCHF2) < 1599 kJ mol(-1).