Isotope enrichment in neon clusters grown in helium nanodroplets
| Autor: | Michael Gatchell, Olof Echt, Paul Scheier, Lukas Tiefenthaler, Klavs Hansen, Siegfried Kollotzek |
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| Jazyk: | angličtina |
| Rok vydání: | 2022 |
| Předmět: |
Materials science
FOS: Physical sciences General Physics and Astronomy chemistry.chemical_element 010402 general chemistry 01 natural sciences Molecular physics Dissociation (chemistry) Ion Neon symbols.namesake Ionization 0103 physical sciences Physics::Atomic and Molecular Clusters Cluster (physics) Physics::Atomic Physics Physics - Atomic and Molecular Clusters Physical and Theoretical Chemistry Helium Debye model 010304 chemical physics Isotope 0104 chemical sciences chemistry symbols Atomic and Molecular Clusters (physics.atm-clus) |
| Popis: | Neon cluster ions Ne$_s^+$ grown in pre-ionized, mass-to-charge selected helium nanodroplets (HNDs) reveal a strong enrichment of the heavy isotope $^{22}$Ne that depends on cluster size s and the experimental conditions. For small sizes the enrichment is much larger than previously reported for bare neon clusters grown in nozzle expansions and subsequently ionized. The enrichment is traced to the massive evaporation of neon atoms in a collision cell that is used to strip helium from the HNDs. We derive a relation between the enrichment of $^{22}$Ne in the cluster ion and its corresponding depletion factor $F$ in the vapor phase. The value thus found for $F$ is in excellent agreement with a theoretical expression that relates isotopic fractionation in two-phase equilibria of atomic gases to the Debye temperature. Furthermore, the difference in zero-point energies between the two isotopes computed from F agrees reasonably well with theoretical studies of neon cluster ions that include nuclear quantum effects in the harmonic approximation. Another fitting parameter provides an estimate for the size s$_i$ of the precursor of the observed Ne$_s^+$. The value is in satisfactory agreement with the size estimated by modeling the growth of Ne$_s^+$, and with lower and upper limits deduced from other experimental data. On the other hand, neon clusters grown in neutral HNDs that are subsequently ionized by electron bombardment exhibit no statistically significant isotope enrichment at all. The finding suggests that the extent of ionization-induced dissociation of clusters embedded in HNDs is considerably smaller than for bare clusters. 14 pages, 5 figures, supplementary material |
| Databáze: | OpenAIRE |
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