Influence of clustering and molecular orbital shapes on the ionization enhancement in ammonia

Scott G. Sayres, Matt W. Ross, A. W. Castleman

Research output: Contribution to journalArticlepeer-review

17 Scopus citations


The Coulomb explosion of clusters is known to be an efficient source for producing multiply charged ions through an enhanced ionization process. However, the factors responsible for obtaining these high charge states have not been previously explored in detail and remain poorly understood. By comparing intensity-resolved visible laser excitation experiments with semi-classical theory over a range spanning both multiphoton and tunneling ionization regimes, we reveal the mechanism in which extreme ionization proceeds. Under laser conditions that can only singly ionize individual molecules, ammonia clusters generate ions depleted of all valence electrons. The geometries of the molecular orbitals are revealed to be important in driving the ionization, and can be entirely emptied at the energy requirement for removal of the first electron in the orbital. The results are in accord with non-sequential ionization arising from electrons tunneling from three separate molecular orbitals aided through the ionization ignition mechanism.

Original languageEnglish (US)
Pages (from-to)12231-12239
Number of pages9
JournalPhysical Chemistry Chemical Physics
Issue number26
StatePublished - Jul 14 2011
Externally publishedYes

ASJC Scopus subject areas

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry


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