An experimental and quasiclassical trajectory study of the rovibrationally state-selected reactions: HD{sup +}(v=0-15,j=1)+He{yields}HeH{sup +}(HeD{sup +})+D(H)
- Department of Chemistry, University of California at Davis, One Shields Avenue, Davis, California 95616 (United States)
The absolute integral cross sections for the formation of HeH{sup +} and HeD{sup +} from the collisions of HD{sup +}(v,j=1)+He have been examined over a broad range of vibrational energy levels v=0-13 at the center-of-mass collision energies (E{sub T}) of 0.6 and 1.4 eV using the vacuum ultraviolet (VUV) pulsed field ionization photoelectron secondary ion coincidence method. The E{sub T} dependencies of the integral cross sections for products HeH{sup +} and HeD{sup +} from HD{sup +}(v=0-4)+He collisions in the E{sub T} range of 0-3 eV have also been measured using the VUV photoionization guided ion beam mass spectrometric technique, in which vibrationally selected HD{sup +}(v) reactant ions were prepared via excitation of selected autoionization resonances of HD. At low total energies, a pronounced isotope effect is observed in absolute integral cross sections for the HeH{sup +}+D and HeD{sup +}+H channels with significant favoring of the deuteron transfer channel. As v is increased in the range of v=0-9, the integral cross sections of the HeH{sup +}+D channel are found to approach those of HeD{sup +}+H. The observed velocity distributions of products HeD{sup +} and HeH{sup +} are consistent with an impulsive or spectator-stripping mechanism. Detailed quasiclassical trajectory (QCT) calculations are also presented for HD{sup +}(v,j=1)+He collisions at the same energies of the experiment. The QCT calculations were performed on the most accurate ab initio potential energy surface available. If the zero-point energy of the reaction products is taken into account, the QCT cross sections for products HeH{sup +} and HeD{sup +} from HD{sup +}(v)+He are found to be significantly lower than the experimental results at E{sub T} values near the reaction thresholds. The agreement between the experimental and QCT cross sections improves with translational energy. Except for prethreshold reactivity, QCT calculations ignoring the zero-point energy in the products are generally in good agreement with experimental absolute cross sections. The experimental HeH{sup +}/HeD{sup +} branching ratios for the HD{sup +}(v=0-9)+He collisions are generally consistent with QCT predictions. The observed isotope effects can be rationalized on the basis of differences in thermochemical thresholds and angular momentum conservation constraints.
- OSTI ID:
- 20991284
- Journal Information:
- Journal of Chemical Physics, Vol. 126, Issue 23; Other Information: DOI: 10.1063/1.2743027; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0021-9606
- Country of Publication:
- United States
- Language:
- English
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