Showing papers by "Tilmann D. Märk published in 1989"
TL;DR: In this article, a double focussing sector field mass spectrometer (reversed geometry) with an improved ion transmission characteristic was used to measure the electron impact ionization cross-sections.
35 citations
TL;DR: In this article, the Coulomb explosion of doubly charged cluster ions Ar n 2+ (with sizes below the appearance size n 2 ) was shown to occur within 1 μs after ion formation.
33 citations
TL;DR: In this article, the appearance of multiply charged cluster ions was determined and the electron energy dependence of singly and doubly charged cluster ion was studied in view of various theoretical considerations and previous results.
Abstract: Kr clusters produced in a supersonic nozzle expansion have been studied by electron impact ionization mass spectrometry. Mass resolved spectra (with n up to 180) show two homologous series consisting of Kr+n and Kr2+n ions. The distribution of Kr+n ions shows distinct magic number effects, the observed abundance anomalies being very similar to the ones observed in Ar and Xe. This confirms the superior stability of closed‐shell and ‐subshell icosahedral structures. Moreover, we have found evidence for the occurrence of Kr3+n and Kr4+n ions. It was possible to determine appearance sizes of these multiply charged cluster ions (yielding n2=69, n3=156, and n4=264), and to study the electron energy dependence of singly and doubly charged cluster ions (yielding a linear threshold law). These results are discussed in view of various theoretical considerations and previous results where available.
28 citations
13 citations
TL;DR: In this article, the decomposition of metastable (N 2 ) n + *, ((N 2 ] n O 2 ) + * and (0 2 )n + * ions (n up to 10) has been studied quantit a double-focusing sector field mass spectrometer as a function of cluster size n, and the number of evaporated neutral monomers p (with p up to n -1 for each cluster ion series).
13 citations
TL;DR: In this paper, the appearance energy of doubly charged van der Waals cluster ions with sizes down to n2=47 at lifetimes of ∼400 μs was observed.
Abstract: In previous experiments on doubly charged Xe clusters, no Xe2+n cluster ions were observed for n less than 53 atoms and no Xe3+n for n less than 114 atoms. From recent computer simulations it was inferred that Xe2+51 ions have lifetimes ∼100 ps while Xe2+55 ions have lifetimes ∼10 μs in agreement with these previous experimental results. Using a high performance mass spectrometer we have repeated these experiments. In contrast to these earlier findings, we are here able to observe doubly charged Xe cluster ions with sizes down to n2=47 (at lifetimes of ∼400 μs). The critical appearance size for triply charged Xe clusters is n3=108. In accordance with a recently suggested sequential ionization mechanism for the production of stable doubly charged van der Waals cluster ions, the appearance energy of Xe2+n was found to lie well below the appearance energy of Xe2+ from Xe.
13 citations
TL;DR: In this paper, the first well resolved SO2 cluster ion spectrum showing doubly charged parent and fragment ions was reported, and the critical appearance size for doublycharged SO2 clusters is n2=21 and for triply charged SO 2 clusters n3=49.
Abstract: We report the first well resolved SO2 cluster ion spectrum showing doubly charged parent and fragment ions. The critical appearance size deduced for doubly charged SO2 clusters is n2=21 and for triply charged SO2 clusters n3=49. This result is compared with theoretical predictions.
6 citations
TL;DR: In this article, the appearance sizes of multiply charged cluster ions were determined and the appearance energies of multiplycharged cluster ions determined are shifted way below the appearance energy of the respective monomer ions.
Abstract: Clusters of Ar, Kr, Xe, N2, O2, CO2, SO2 and NH3 formed by supersonic nozzle expansion have been studied by electron impact ionization mass spectrometry (up to 15000 amu). Besides mass spectra of singly charged ions showing the characteristic anomalous distributions, we have in particular investigated the properties of multiply charged cluster ions. Critical appearance sizes of doubly and triply charged cluster ions, n2 and n3 respectively, found in the present study confirm recent theoretical predictions about n3/n2 and their dependence on the properties of the cluster constituents. The appearance energies of multiply charged cluster ions determined are shifted way below the appearance energies of the respective monomer ions. These huge red shifts together with the observed linear threshold laws and large maximum ionization efficiencies indicate that multiply charged cluster ions are produced by sequential single ionization events of one incoming electron at different cluster sites. Furthermore, we have also obtained for the first time clear evidence that (for electron energies above the appearance energy of doubly charged ions) an appreciable amount of singly charged (also fragment) ions is produced via Coulomb explosion of unstable doubly charged ions in the ion source.
4 citations
TL;DR: In this article, the mass spectral peaks attributed to doubly charged NH 3 clusters (produced by electron impact ionization) are each composed of seven individual peaks and two smaller peaks to the left of the parent peak (NH 3 n 2+ were explained as being due to unimolecular fragmentation processes within such parent ions.
3 citations
TL;DR: In this paper, it was found that the individual metastable reaction rates k depend strongly on cluster size and cluster ion production pathways and that there exists experimental evidence (k = k(t)) and a theoretical prediction that a given mass selected cluster ion generated by electron impact ionization of a nozzle expansion beam will comprise a range of metastable decay rates.
Abstract: Metastable decay of cluster ions has been discovered only recently. It was noted that one has to take this metastable decay into account when using mass spectrometry to probe neutral clusters, because ion abundance anomalies in mass spectra of rare gas and molecular clusters are caused by delayed metastable evaporation of monomers following ion production. Moreover, it was found that (i) the individual metastable reaction rates k depend strongly on cluster size and cluster ion production pathways and that (ii) there exists experimental evidence (k = k(t)) and a theoretical prediction that a given mass selected cluster ion generated by electron impact ionization of a nozzle expansion beam will comprise a range of metastable decay rates. In addition, it was discovered that metastable Ar cluster ions which lose two monomers in the μs time regime decay via sequential decay series Ar+* n → Ar+* n−1 → Ar+* n−2 with cluster sizes 7 ≤ n ≤ 10 and n = 3 (similar results were obtained recently in case of N2 cluster ions). Conversely, the dominant metastable decay channel of Ar+* 4 into Ar+ 2 was found to proceed predominantly via a single step fissioning process.
3 citations
TL;DR: In this paper, the authors have observed photodissociation of neutral van der Waals clusters induced by visible laser light using coaxial interaction between the beams and suggest that excitation via Raman scattering is the origin of this phenomenon.
Abstract: Recently we have observed [1–4] photodissociation of neutral van der Waals clusters induced by visible laser light using coaxial interaction between the beams. Because of possible artifacts we have repeated here this experiment in a crossed beam configuration. The present results confirm the occurrence of this photodissociation effect. We suggest tentatively that excitation via Raman scattering is the origin of this phenomenon.
TL;DR: In this article, it was shown that metastable N2 cluster ions lose more than one N2 molecule in the μs time regime and decay predominantly via sequential series (N2)+* n → (N 2 ) → n−1 → N−2 → N+2, evaporating a single monomer in each successive decay steps.
Abstract: N2 cluster ions are produced by electron impact ionization of a supersonic N2 cluster beam and analyzed with a double focussing sector field mass spectrometer. It is found that metastable N2 cluster ions lose more than one N2 molecule in the μs time regime and decay predominantly via sequential series (N2)+* n → (N2)+* n−1 → … → N+ 2, evaporating a single monomer in each of these successive decay steps. The metastable decay rates determined in detail for cluster sizes 2 ≤ n ≤ 6 and n = 20 lie between 1 and 106 s−1. These rates (i) depend strongly on the time elapsed after ion formation and on the respective parent cluster ion size, and (ii) exhibit a quasiperiodic pattern in magnitude.
TL;DR: In this paper, an apparent photodestruction (using visible laser light) of a neutral Ar n cluster beam produced in a supersonic expansion was observed, and the clusters were detected by electron ionization/mass spectrometry.
TL;DR: In this paper, electron attachment and electron impact ionization of SF6 clusters were investigated quantitatively in a molecular beam/electron ion source/mass spectrometer system as a function of electron energy E (0≤E≤180 eV).
Abstract: Electron attachment and electron impact ionization of SF6 clusters have been investigated quantitatively in a molecular beam/electron ion source/mass spectrometer system as a function of electron energy E (0≤E≤180 eV) and as a function of cluster size.
TL;DR: In this article, strong photodissociation (using visible laser light) of neutral van der Waals clusters (Ar, N2, O2, CO2, SO2, NH3) was observed by supersonic expansion and detected by electron ionization/mass spectrometer.
Abstract: We have observed strong photodissociation (using visible laser light) of neutral van der Waals clusters (Ar, N2, O2, CO2, SO2, NH3) produced by supersonic expansion and detected by electron ionization/mass spectrometer. Several tests were performed, all of them supporting this surprising discovery. We suggest that Raman induced photodissociation (RIP) is responsible for this phenomenon. This first observation of Raman induced photodissociation provides a new technique for the study of neutral van der Waals clusters.