Electron impact ionization of size selected hydrogen clusters (H{sub 2}){sub N}: Ion fragment and neutral size distributions
- Max-Planck-Institut fuer Dynamik und Selbstorganisation Bunsenstrasse 10, D-37073 Goettingen (Germany)
Clusters consisting of normal H{sub 2} molecules, produced in a free jet expansion, are size selected by diffraction from a transmission nanograting prior to electron impact ionization. For each neutral cluster (H{sub 2}){sub N} (N=2-40), the relative intensities of the ion fragments H{sub n}{sup +} are measured with a mass spectrometer. H{sub 3}{sup +} is found to be the most abundant fragment up to N=17. With a further increase in N, the abundances of H{sub 3}{sup +}, H{sub 5}{sup +}, H{sub 7}{sup +}, and H{sub 9}{sup +} first increase and, after passing through a maximum, approach each other. At N=40, they are about the same and more than a factor of 2 and 3 larger than for H{sub 11}{sup +} and H{sub 13}{sup +}, respectively. For a given neutral cluster size, the intensities of the ion fragments follow a Poisson distribution. The fragmentation probabilities are used to determine the neutral cluster size distribution produced in the expansion at a source temperature of 30.1 K and a source pressure of 1.50 bar. The distribution shows no clear evidence of a magic number N=13 as predicted by theory and found in experiments with pure para-H{sub 2} clusters. The ion fragment distributions are also used to extract information on the internal energy distribution of the H{sub 3}{sup +} ions produced in the reaction H{sub 2}{sup +}+H{sub 2}{yields}H{sub 3}{sup +}+H, which is initiated upon ionization of the cluster. The internal energy is assumed to be rapidly equilibrated and to determine the number of molecules subsequently evaporated. The internal energy distribution found in this way is in good agreement with data obtained in an earlier independent merged beam scattering experiment.
- OSTI ID:
- 21104049
- Journal Information:
- Journal of Chemical Physics, Vol. 128, Issue 19; Other Information: DOI: 10.1063/1.2903451; (c) 2008 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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