Reactions of CO2 with H, H2 and deuterated analogues

Combining a temperature variable 22-pole ion trapwith a cold effusive beam of neutrals, rate coefficients k(T) have beenmeasured for reactions of CO2 ionswithH,H2 anddeuterated analogues. The neutral beam which is cooled in an accommodator to TACC, penetrates the trapped ion cloud with a well-characterized velocity distribution. The temperature of the ions, T22PT, has been set to values between 15 and 300K. Thermalization is accelerated by using helium buffer gas. For reference, some experiments have been performed with thermal target gas. For this purpose hydrogen is leaked directly into the box surrounding the trap. While collisions of CO2 with H2 lead exclusively to the protonated product HCO2, collisions with H atoms form mainly HCO+. The electron transfer channel H+ +CO2 could not be detected (<20%). Equivalent studies have been performed for deuterium. The rate coefficients for reactions with atoms are rather small. Within our relative errors of less than 15%, they do not depend on the temperature of the CO2 ions nor on the velocity of the atoms (k(T) lays between 4.5 and 4.7×10−10 cm3 s−1 with H as target, and 2.2×10−10 cm3 s−1 with D). For collisions with molecules, the reactivity increases significantly with falling temperature, reaching the Langevin values at 15K. These results are reported as k= ̨ (T/300K)ˇ with ̨=9.5×10−10 cm3 s−1 and ˇ =−0.15 for H2 and ̨=4.9×10−10 cm3 s−1 and ˇ =−0.30 for D2. © 2008 Elsevier B.V. All rights reserved.