A state-selected study of the H2+ (X,v+=0-17,N+=1)+Ne proton transfer reaction using the pulsed-field ionization-photoelectron-secondary ion coincidence scheme

The endothermic proton transfer reaction, H-2(+)(v(+),N+=1)+Ne-->NeH++H(DeltaH=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(+)=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-T=0.7 eV, absolute state-selected reaction cross sections are measured for all reactant vibrational levels v(+)=0-17. For levels v(+)=0-6, the cross sections grow rapidly with vibrational quantum, above which the cross sections saturate at a value of similar to13+/-4 Angstrom(2). At levels v(+)>13, the cross sections decline, probably due to competition with the dissociation channel. At a translational energy, E-T=1.7 eV, absolute state-selected reaction cross sections are measured for reactant vibrational levels spanning the range between v(+)=0 and 14. Cross section growth is observed from v(+)=0-7, above which the cross sections no longer exhibit a steady trend. At E-T=4.5 eV, cross sections are reported for vibrational levels covering the range between v(+)=0 and 12. The cross sections are substantially lower at this high translational energy, however, they still exhibit a substantial vibrational enhancement below v(+)=8. The present measurements are compared with quasiclassical trajectory (QCT) calculations. The comparison can be categorized by three distinct total energy (E-tot=E-T+E-vib) regimes. For E-tot<1 eV, the experimental cross sections exceed the QCT results, consistent with important quantum effects at low energies. For 1<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. (C) 2003 American Institute of Physics.