A pulsed-field ionization photoelectron secondary ion coincidence study of the H2+(X,υ+=–15,N+=1)+He proton transfer reaction

Abstract

The endothermic proton transfer reaction, H2+(upsilon+)+He-->HeH+ + H(DeltaE=0.806 eV), is investigated over a broad range of reactant vibrational levels using high-resolution vacuum ultraviolet to prepare reactant ions either through excitation of autoionization resonances, or using the pulsed-field ionization-photoelectron-secondary ion coincidence (PFI-PESICO) approach. In the former case, the translational energy dependence of the integral reaction cross sections are measured for upsilon+=0-3 with high signal-to-noise using the guided-ion beam technique. PFI-PESICO cross sections are reported for upsilon+=1-15 and upsilon+=0-12 at center-of-mass collision energies of 0.6 and 3.1 eV, respectively. All ion reactant states selected by the PFI-PESICO scheme are in the N+=1 rotational level. The experimental cross sections are complemented with quasiclassical trajectory (QCT) calculations performed on the ab initio potential energy surface provided by Palmieri et al. [Mol. Phys. 98, 1839 (2000)]. The QCT cross sections are significantly lower than the experimental results near threshold, consistent with important contributions due to resonances observed in quantum scattering studies. At total energies above 2 eV, the QCT calculations are in excellent agreement with the present results. PFI-PESICO time-of-flight (TOF) measurements are also reported for upsilon+=3 and 4 at a collision energy of 0.6 eV. The velocity inverted TOF spectra are consistent with the prevalence of a spectator-stripping mechanism.

A time-dependent wave-packet quantum scattering study of the reaction H2+(v=–2,4,6;j=1)+He→HeH++H

“…It can be seen that the present j = 1 calculation yields almost the same thresholds as the deconvoluted LOC fit to the experimental cross sections. If we consider that the experimental total absolute cross sections have an error of 25%, 41 we can conclude that a reasonable agreement has been achieved between the experimental and the theoretical cross sections. For v = 0 cross sections ͓Fig.…”

“…All these three studies achieved the vibrational state preparation of H 2 + by vuv photoionization at selected autoionization lines of H 2 . As pointed out recently by Tang et al, 41 41 Again, the more gradual rise of the experimental cross sections near the reaction threshold results from the broadening effect of the reactant H 2 + ion-beam kinetic-energy resolution. Some minor structures attributable to reactive resonances can be seen in the theoretical cross-section curves.…”

“…Recently, Palmieri et al 9 have constructed a new ab initio PES, which is currently recognized to be the most accurate PES for the H 2 + + He reaction system. This, along with the most recent experimental efforts by Tang et al, 41 has stimulated new theoretical interest for quantum scattering studies of this model ion-molecule reaction system.…”

“…7, the present theoretical total cross sections with v = 2 and j = 1 plotted as a function of total energy are compared to those of the recent CS time-dependent calculation for j = 0 by Panda et al 33 and the time-independent calculation by Palmieri et al 9 This comparison with the two quantum theoretical calculations using the same potential-energy surface of Palmieri et al 9 clearly shows that the present results are much closer to the results of the exact calculation by Palmieri et al 9 The resonances and trend in the cross sections are quite different between the CS results of Panda et al 33 and the present CC results. A detailed comparison of available experimental and theoretical cross sections for the H 2 + ͑v = 0-3͒ + He proton transfer reaction in the collision energy range of 0.0-2.0 eV has been made recently by Tang et al 41 Here, we have included in Fig. 7 the experimental cross sections obtained by Tang et al 41 and Turner et al 37 using a vacuum ultraviolet ͑vuv͒ photoionization guide ion-beam ion-molecule reaction apparatus, together with those derived by the measurements of Chupka et al…”

“…A detailed comparison of available experimental and theoretical cross sections for the H 2 + ͑v = 0-3͒ + He proton transfer reaction in the collision energy range of 0.0-2.0 eV has been made recently by Tang et al 41 Here, we have included in Fig. 7 the experimental cross sections obtained by Tang et al 41 and Turner et al 37 using a vacuum ultraviolet ͑vuv͒ photoionization guide ion-beam ion-molecule reaction apparatus, together with those derived by the measurements of Chupka et al…”