Reactions of Ar+with H2, N2, O2, and CO at 20, 30, and 70 K

摘要

Reactions of Ar+(2P3/2) ions with H2, N2, O2, and CO have been studied with the CRESU apparatus at 30 K in argon buffer gas and with the newly developed masshyphen;selected ion injector (CRESUS configuration) at 20 and 70 K in helium buffer gas. The atom exchange reaction with H2is rather fast, with a rate coefficientkshowing a small energy dependence well represented byk=1.5times;10minus;9E0.16cm3thinsp;sminus;1with the collision energy in the centerhyphen;ofhyphen;mass frame,E, in the range 2.5times;10minus;3minus;0.65 eV. This result is more compatible with a frozenhyphen;rotor capture model rather than with a threshold model for endoergic reactions. Concerning the reaction with N2, a competition between the two exit channels involving the two first vibrational levels of the N+2product ion explains the minimum of the rate constant suggested at about 140 K by previous SIFT experiments lsqb;D. Smith and N. G. Adams, Phys. Rev. A23, 2327 (1981)rsqb; and presently confirmed. The rate coefficients for the charge transfer reactions with O2and CO increase with decreasing energy, i.e.,k=9.6times;10minus;12Eminus;0.51andk=1.1times;10minus;11Eminus;0.47cm3thinsp;sminus;1, respectively, forEin the range 2.5times;10minus;3minus;0.3 eV. Both these reactions proceed via an intimate collision mechanism.