High-resolution pulsed field ionization photoelectron{endash}photoion coincidence study of CH{sub 4}: Accurate 0 K dissociation threshold for CH{sub 3}{sup +}
- Freie Universitaet Berlin, Institut fuer Chemie, Physikalische und Theoretische Chemie, Takustrasse 3, 14195 Berlin (Germany)
- Lawrence Berkeley National Laboratory, Chemical Science Division, Berkeley, California 94720 (United States)
- Department of Chemistry, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3290 (United States)
- Ames Laboratory, USDOE and Iowa State University, Department of Chemistry, Ames, Iowa 50011 (United States)
The formation of methyl cation (CH{sub 3}{sup +}) from methane (CH{sub 4}) has been investigated in high resolution using the newly perfected pulsed field ionization photoelectron{endash}photoion coincidence (PFI-PEPICO) scheme. The PFI-PEPICO data reveal that fragmentation of CH{sub 4} in high-{ital n} Rydberg states occurs at energies above the dissociation threshold prior to pulsed field ionization. The crossover point of the breakdown curves is found to depend strongly on the Stark field in the ion source and thus traditional simulation procedures based on such a feature for ion dissociation energy determination are not appropriate in PFI-PEPICO studies. We show that for a prompt dissociation process, the disappearance energy of the parent molecule provides an accurate measure of the 0 K ion dissociation threshold, as that for CH{sub 3}{sup +} from CH{sub 4} is 14.323{plus_minus}0.001 eV. {copyright} {ital 1999 American Institute of Physics.}
- OSTI ID:
- 687990
- Journal Information:
- Journal of Chemical Physics, Vol. 111, Issue 18; Other Information: PBD: Nov 1999
- Country of Publication:
- United States
- Language:
- English
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