Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

The Journal of Chemical Physics

Measurements of the lifetimes of electron bubbles in large size selected HeN−4 droplets

Michal Fárnı́k, B. Samelin, Jan Peter Toennies

Published May 8, 1999• 49 citations
Publisher

Abstract

The lifetimes of electron bubbles in large size selected HeN−4 droplets have been measured in a molecular beam experiment to lie between 2⋅10−3 and 0.2 s in droplets with sizes between N≈105 and 107 atoms, respectively. The dependence of the lifetimes on the electric fields used to size select the droplets, on the energies of the incident electrons, and on the infrared radiation emitted from the apparatus walls were investigated and taken into account. The experimental lifetimes are many orders of magnitude smaller than predicted by earlier theories but consistent with a recent theory published by the authors in Phys. Rev. Lett. 81, 3892 (1998).

DOI
10.1063/1.478842

Related papers

The influence of embedded atoms, molecules, and clusters on the lifetimes of electron bubbles in large He4 droplets

Michal Fárnı́k, Jan Peter Toennies

The lifetimes of electrons injected into large (≈106 atoms) superfluid He4 droplets have been measured in the presence of different prior embedded rare gas atoms, their clusters, and the molecules O2, H2O, and SF6. For the light rare gas atoms Ne and Ar the lifetimes of about 6⋅10−2 s, found previously for pure droplets, are reduced to between 1–2⋅10−2 s. Single molecules with large electron affinities, such as SF6 and O2 and small clusters of H2O lead to a significant increase in the lifetimes. In the case of Kr and Xe, larger clusters with n̄>14 are needed before the lifetimes increase. A simple model, which takes account of the energy levels occupied by the electrons in the corresponding molecules or the clusters, assumed to be solid, can qualitatively explain the observations.

The Journal of Chemical Physics•Feb 14, 2003•25 citations

Differences in the Detachment of Electron Bubbles from Superfluid 4He Droplets versus Nonsuperfluid 3He Droplets

Michal Fárnı́k, Ulrich Henne, B. Samelin +1 more

The rate of detachment of electron bubbles inside size-selected ${}^{4}\mathrm{He}$ and ${}^{3}\mathrm{He}$ droplets ( ${10}^{5}--{10}^{7}$ atoms) has been measured. At zero electric field the lifetimes of ${}^{4}\mathrm{He}$ droplets increase with size from ${10}^{\ensuremath{-}3}$ to 0.2 s, orders of magnitude smaller than previously predicted. With increasing fields the detachment gradually increases for ${}^{4}\mathrm{He}$ droplets, whereas a sharp threshold was found at 1.45 kV/cm for ${}^{3}\mathrm{He}$ droplets, independent of size. A simple dynamical model which accounts for superfluidity in the ${}^{4}\mathrm{He}$ droplets versus a viscous dynamics in ${}^{3}\mathrm{He}$ can explain the observations.

Physical Review Letters•Nov 2, 1998•40 citations

Experimental and theoretical study of the radial density distributions of large 3He droplets

Jan Harms, Jan Peter Toennies, M. Barranco +1 more

The integral cross sections of large ${}^{3}\mathrm{He}$ droplets and the number of atoms in the corresponding droplets $(\overline{N}=2\ifmmode\times\else\texttimes\fi{}{10}^{3}--2\ifmmode\times\else\texttimes\fi{}{10}^{4}\mathrm{atoms})$ have been measured in molecular-beam scattering experiments. The experimental results are in very good agreement with integral cross sections calculated from the radial density distributions predicted from density-functional theory calculations. The experimentally confirmed theoretical 10--90% surface thicknesses vary between 8.0 \AA{} $(\overline{N}{=10}^{3})$ and 7.6 \AA{} $(\overline{N}=4\ifmmode\times\else\texttimes\fi{}{10}^{4})$ and are about 30% larger than calculated for ${}^{4}\mathrm{He}$ droplets of similar sizes.

Physical review. B, Condensed matter•Apr 20, 2001•42 citations

Formation of He4+ via electron impact of helium droplets

J. Fine, Deepak Verma, Curtis F. Jones +2 more

Electron impact ionization of superfluid helium droplets containing several thousand atoms produces a broad distribution of Hen+ ions that peaks at n = 2 and decreases monotonically toward larger n. In larger droplets (say 105 or more atoms), however, the He4+ signal intensity is anomalously large. We have studied the mechanism for the formation of He4+ ions in large helium droplets by varying the duration of the electron impact excitation pulse. Droplets of different average sizes were generated using the expansion of helium at 20 bars and 9-20 K through a pulsed valve nozzle. The resulting ions were analyzed by time-of-flight mass spectroscopy (TOFMS) and quadrupole mass spectroscopy (QMS). The intensity distributions obtained with the TOFMS technique initially showed much smaller He4+ signals than those obtained using QMS. However, we discovered that the intensity anomaly is associated with the duration of the electron bombardment pulse in the TOFMS instrument. Measurements with different electron bombardment pulse durations enabled us to discern a characteristic time of ∼10 μs for enhanced He4+ production in large droplets under our experimental conditions. A qualitative model is presented in which metastables interact on droplet surfaces, yielding two He2+ cores that share a Rydberg electron while minimizing repulsion between the cores. This is the He4+(4A2) state suggested by Knowles and Murrell.

The Journal of Chemical Physics•Jan 23, 2018•11 citations

Electron Ionization of Size-Selected Positively and Negatively Charged Helium Droplets

Felix Laimer, Fábio Zappa, Elisabeth Gruber +1 more

A beam of size-selected charged helium droplets was crossed with an electron beam, and the ion efficiency curves for the product droplets in all different charge states were recorded. We estimate that the selected helium droplets on their passage through the electron beam are hit by several hundred electrons which can interact with the individual He atoms of the droplets. Reaction channels corresponding to the removal or capture of up to eight electrons were identified, and in all cases, inelastic scattering and the formation of metastable helium played a significant role.

Atoms•Oct 5, 2021•5 citations

Sizes of large He droplets

Luis F. Gomez, Evgeny Loginov, Russell Sliter +1 more

Helium droplets spanning a wide size range, N(He) = 10(3)-10(10), were formed in a continuous-nozzle beam expansion at different nozzle temperatures and a constant stagnation pressure of 20 bars. The average sizes of the droplets have been obtained by attenuation of the droplet beam through collisions with argon and helium gases at room temperature. The results obtained are in good agreement with previous measurements in the size range N(He) = 10(5)-10(7). Moreover, the measurements give the average sizes in the previously uncharacterized range of very large droplets of 10(7)-10(10) atoms. The droplet sizes and beam flux increase rapidly at nozzle temperatures below 6 K, which is ascribed to the formation of droplets within the nozzle interior. The mass spectra of the droplet beam upon electron impact ionization have also been obtained. The spectra show a large increase in the intensity of the He(4) (+) signal upon increase of the droplet size, an effect which can be used as a secondary size standard in the droplet size range N(He) = 10(4)-10(9) atoms.

The Journal of Chemical Physics•Oct 18, 2011•180 citations
The lifetimes of electron bubbles in large size selected HeN−4 droplets have been measured in a molecular beam experiment to lie between 2⋅10−3 and 0.2 s in droplets with sizes between N≈105 and 107 atoms, respectively. The dependence of the lifetimes on the electric fields used to size select the droplets, on the energies of the incident electrons, and on the infrared radiation emitted from the apparatus walls were investigated and taken into account. The experimental lifetimes are many orders of magnitude smaller than predicted by earlier theories but consistent with a recent theory published by the authors in Phys. Rev. Lett. 81, 3892 (1998).
The lifetimes of electrons injected into large (≈106 atoms) superfluid He4 droplets have been measured in the presence of different prior embedded rare gas atoms, their clusters, and the molecules O2, H2O, and SF6. For the light rare gas atoms Ne and Ar the lifetimes of about 6⋅10−2 s, found previously for pure droplets, are reduced to between 1–2⋅10−2 s. Single molecules with large electron affinities, such as SF6 and O2 and small clusters of H2O lead to a significant increase in the lifetimes. In the case of Kr and Xe, larger clusters with n̄>14 are needed before the lifetimes increase. A simple model, which takes account of the energy levels occupied by the electrons in the corresponding molecules or the clusters, assumed to be solid, can qualitatively explain the observations.
The rate of detachment of electron bubbles inside size-selected 4He{}^{4}\mathrm{He}4He and 3He{}^{3}\mathrm{He}3He droplets ( 105−−107{10}^{5}--{10}^{7}105−−107 atoms) has been measured. At zero electric field the lifetimes of 4He{}^{4}\mathrm{He}4He droplets increase with size from ${10}^{\ensuremath{-}3}$ to 0.2 s, orders of magnitude smaller than previously predicted. With increasing fields the detachment gradually increases for 4He{}^{4}\mathrm{He}4He droplets, whereas a sharp threshold was found at 1.45 kV/cm for 3He{}^{3}\mathrm{He}3He droplets, independent of size. A simple dynamical model which accounts for superfluidity in the 4He{}^{4}\mathrm{He}4He droplets versus a viscous dynamics in 3He{}^{3}\mathrm{He}3He can explain the observations.
The integral cross sections of large 3He{}^{3}\mathrm{He}3He droplets and the number of atoms in the corresponding droplets $(\overline{N}=2\ifmmode\times\else\texttimes\fi{}{10}^{3}--2\ifmmode\times\else\texttimes\fi{}{10}^{4}\mathrm{atoms})$ have been measured in molecular-beam scattering experiments. The experimental results are in very good agreement with integral cross sections calculated from the radial density distributions predicted from density-functional theory calculations. The experimentally confirmed theoretical 10--90% surface thicknesses vary between 8.0 \AA{} (N‾=103)(\overline{N}{=10}^{3})(N=103) and 7.6 \AA{} $(\overline{N}=4\ifmmode\times\else\texttimes\fi{}{10}^{4})$ and are about 30% larger than calculated for 4He{}^{4}\mathrm{He}4He droplets of similar sizes.
Electron impact ionization of superfluid helium droplets containing several thousand atoms produces a broad distribution of Hen+ ions that peaks at n = 2 and decreases monotonically toward larger n. In larger droplets (say 105 or more atoms), however, the He4+ signal intensity is anomalously large. We have studied the mechanism for the formation of He4+ ions in large helium droplets by varying the duration of the electron impact excitation pulse. Droplets of different average sizes were generated using the expansion of helium at 20 bars and 9-20 K through a pulsed valve nozzle. The resulting ions were analyzed by time-of-flight mass spectroscopy (TOFMS) and quadrupole mass spectroscopy (QMS). The intensity distributions obtained with the TOFMS technique initially showed much smaller He4+ signals than those obtained using QMS. However, we discovered that the intensity anomaly is associated with the duration of the electron bombardment pulse in the TOFMS instrument. Measurements with different electron bombardment pulse durations enabled us to discern a characteristic time of ∼10 μs for enhanced He4+ production in large droplets under our experimental conditions. A qualitative model is presented in which metastables interact on droplet surfaces, yielding two He2+ cores that share a Rydberg electron while minimizing repulsion between the cores. This is the He4+(4A2) state suggested by Knowles and Murrell.
A beam of size-selected charged helium droplets was crossed with an electron beam, and the ion efficiency curves for the product droplets in all different charge states were recorded. We estimate that the selected helium droplets on their passage through the electron beam are hit by several hundred electrons which can interact with the individual He atoms of the droplets. Reaction channels corresponding to the removal or capture of up to eight electrons were identified, and in all cases, inelastic scattering and the formation of metastable helium played a significant role.
Helium droplets spanning a wide size range, N(He) = 10(3)-10(10), were formed in a continuous-nozzle beam expansion at different nozzle temperatures and a constant stagnation pressure of 20 bars. The average sizes of the droplets have been obtained by attenuation of the droplet beam through collisions with argon and helium gases at room temperature. The results obtained are in good agreement with previous measurements in the size range N(He) = 10(5)-10(7). Moreover, the measurements give the average sizes in the previously uncharacterized range of very large droplets of 10(7)-10(10) atoms. The droplet sizes and beam flux increase rapidly at nozzle temperatures below 6 K, which is ascribed to the formation of droplets within the nozzle interior. The mass spectra of the droplet beam upon electron impact ionization have also been obtained. The spectra show a large increase in the intensity of the He(4) (+) signal upon increase of the droplet size, an effect which can be used as a secondary size standard in the droplet size range N(He) = 10(4)-10(9) atoms.