| Abstrakt: |
The endothermic proton transfer reaction, H[sub 2][sup +](v[sup +],N[sup +]=1)+Ne→NeH[sup +]+H(ΔH=0.54 eV), is investigated over a broad range of reactant vibrational energies using the pulsed-field ionization–photoelectron–secondary ion coincidence (PFI–PESICO) scheme. For the lowest vibrational levels, v[sup +]=0 and 1, a detailed translational energy dependence is also presented using a continuous approach for preparing reactant ions with monochromatic VUV. Sharp threshold onsets are observed, suggesting the importance of long-lived intermediates or resonances. At a translational energy, E[sub T]=0.7 eV, absolute state-selected reaction cross sections are measured for all reactant vibrational levels v[sup +]=0–17. For levels v[sup +]=0–6, the cross sections grow rapidly with vibrational quantum, above which the cross sections saturate at a value of ∼13±4 Å[sup 2]. At levels v[sup +]>13, the cross sections decline, probably due to competition with the dissociation channel. At a translational energy, E[sub T]=1.7 eV, absolute state-selected reaction cross sections are measured for reactant vibrational levels spanning the range between v[sup +]=0 and 14. Cross section growth is observed from v[sup +]=0–7, above which the cross sections no longer exhibit a steady trend. At E[sub T]=4.5 eV, cross sections are reported for vibrational levels covering the range between v[sup +]=0 and 12. The cross sections are substantially lower at this high translational energy, however, they still exhibit a substantial vibrational enhancement below v[sup +]=8. The present measurements are compared with quasiclassical trajectory (QCT) calculations. The comparison can be categorized by three distinct total energy (E[sub tot]=E[sub T]+E[sub vib]) regimes. For E[sub tot]<1 eV, the experimental cross sections exceed the QCT results, consistent with important quantum effects at low energies. For 1tot<3 eV, excellent agreement is observed between the PFI–PESICO cross sections and the QCT calculations. At total energies exceeding 3 eV, the experimental results are generally higher, probably because QCT overpredicts competition from the dissociation channel. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR] |
