THE HYDROGEN-ATOM ABSTRACTION REACTION CO-]HCO++H - TRANSLATIONAL ANDINTERNAL ENERGY-DEPENDENCE OF THE INTEGRAL CROSS-SECTION(H2)

The widely accepted model descriptions of ion-molecule reactions sugge st identical rate constants for the title reaction and the analogous, isoelectronic system N-2(+)+H-2, which has been the topic of a previou s publication from this laboratory. A comparison of both data sets, ho wever, reveals substantial disagreement which we attribute to the abse nce of energetic resonances between the reagents which characterized t he N-2(+)/H-2 system. Resonantly enhanced photoionization was exploite d to accomplish the state-specific preparation of CO+ (X (2) Sigma(+), upsilon(+) = 0,1). A monoenergetic beam of vibrationally selected ion s, tuned within the range 0.01 eV less than or equal to E(cm)less than or equal to 10 eV, transits a scattering chamber which confines the n eutral, H-2. The title reaction was the only channel observed-no evide nce of charge transfer or dissociative ionization could be detected. T he hydrogen atom transfer turns out to proceed directly. The reactive cross section fails to show the E-1/2 dependence indicative of collisi on determined processes. The experimental data are perfectly mimicked by an expanded Langevin model which includes additional attractive pot ential terms. In contrast to the N-2(+)/H-2 case, vibrational excitati on does not affect the rate of the reaction. (C) 1998 American Institu te of Physics.