Electrostatic Ion Beam Trap Research Articles

Ultraslow isomerization in photoexcited gas-phase carbon cluster {{rm C}}_{10}^ -

Isomerization and carbon chemistry in the gas phase are key processes in many scientific studies. Here we report on the isomerization process from linear {{rm C}}_{10}^ - to its monocyclic isomer. {{rm C}}_{10}^ - ions were trapped in an electrostatic ion beam trap and then excited with a laser pulse of precise energy. The neutral products formed upon photoexcitation were measured as a function of time after the laser pulse. It was found using a statistical model that, although the system is excited above its isomerization barrier energy, the actual isomerization from linear to monocyclic conformation takes place on a very long time scale of up to hundreds of microseconds. This finding may indicate a general phenomenon that can affect the interstellar medium chemistry of large molecule formation as well as other gas phase processes.

Radiative lifetime measurements of 2P3/2 and 2P1/2 metastable levels in triply charged xenon using electrostatic ion beam trap

Abstract The radiative lifetimes of Xe3+ ions in the metastable 5s25p3 2P3/2 and 2P1/2 states were measured by using an electrostatic ion beam trap. The lifetimes were obtained by measuring the number of photons emitted during the 2P3/2 → 2D3/2 (447 nm) and 2P1/2 → 4S3/2 (357 nm) forbidden transitions of Xe3+, as a function of the storage time. The storage lifetime of the Xe3+ was simultaneously measured by detecting the Xe ions with changed charge escaping from the trap, which yielded information pertaining to the correction of the collision-induced loss of Xe3+ in the trap. The obtained lifetimes of 7.0 ± 0.2 ms for the 2P3/2 state and 16.6 ± 0.8 ms for the 2P1/2 state were compared with previously reported theoretical and experimental values.

Autoresonance Cooling of Ions in an Electrostatic Ion Beam Trap.

Autoresonance (AR) cooling of a bunch of ions oscillating inside an electrostatic ion beam trap is demonstrated for the first time. The relatively wide initial longitudinal velocity distribution is reduced by at least an order of magnitude using AR acceleration and ramping forces. The hot ions escaping the bunch are not lost from the system but continue to oscillate in the trap outside of the bunch and may be further cooled by successive AR processes. Ion-ion collisions inside the bunch close to the turning points in the trap's mirrors contribute to the thermalization of the ions. This cooling method can be applied to any mass and any charge.

Radiative lifetime of metastable Xe3+ measured using an electrostatic ion beam trap

SynopsisWe have measured the radiative lifetime of the 2P3/2 metastable level in Xe3+ using an electrostatic ion beam trap. The lifetime was obtained by measuring the number of photons emitted during the 2P3/2→2D3/2 transition of Xe3+ as a function of the storage time. The lifetime is compared with previously reported theoretical and experimental values.

Protein and peptide cross sections and mass spectra in an electrostatic ion beam trap

Among the advantages of an electrostatic ion beam trap (EIBT), which is based on purely electrostatic fields, are mass-unlimited trapping and ease of operation. We have developed a new system that couples an electrospray ion source to an EIBT. Between the source and EIBT there is a Paul trap in which the ions are accumulated before being extracted and accelerated. After the ion bunch has entered the EIBT, the ions are trapped by rapidly raising the voltages on the entrance mirror. The oscillations of the bunch are detected by amplifying the charge induced on a pickup ring in the center of the trap, the ion mass being directly proportional to the square of the oscillation period. The trapping of biomolecules in the RF-bunching mode of the EIBT is used for measurement of mass spectra and collision cross sections. Coalescence of bunches of ions of nearby mass in the self-bunching mode is also demonstrated.

An experimental setup to study delayed electron emission upon photoexcitation of trapped polyatomic anions.

A Velocity Map Imaging (VMI) spectrometer has been designed and integrated with an electrostatic ion beam trap to study delayed electron emission from trapped polyatomic anions upon photodetachment. The VMI spectrometer is small in size and can record a wide range of photoelectron energies, with variable magnification. Delayed electron emission can be recorded in our experimental setup for any time duration after the photoexcitation of the polyatomic anions. Experiments were carried out with trapped O- and C5- ions to demonstrate the capability of the spectrometer. Delayed electron emissions from C5- as well as prompt photoelectrons from O- were detected by the VMI spectrometer upon photoexcitation. The design and performance of the spectrometer are presented in detail.

Radiative lifetime measurement of 1S0 metastable state of Ar2+ using electrostatic ion beam trap

The radiative lifetime of the 3s23p41S0 metastable state of Ar2+ was measured using an electrostatic ion beam trap. The lifetime was obtained by measuring the number of photons emitted during the 1S0→3P1 magnetic dipole transition of Ar2+ as a function of the storage time. The wavelength of the photons was 311nm. To correct for the collision-induced loss of Ar2+ ions in the trap, the storage lifetime of the Ar2+ beam was measured simultaneously by detecting Ar neutrals escaping from the trap. The obtained radiative lifetime was 157±19ms, which was comparable to previously reported theoretical and experimental values.

Formation and stabilization of C6− by radiative electron attachment

Radiative electron attachment (REA) plays an important role in forming molecular anions in various astrophysical environments. In this work, we determined the rate coefficient for the formation of C6− by REA based on a detailed balance approach. C6− ions are stored in an electrostatic ion beam trap and are photoexcited above their adiabatic detachment energy (4.18 eV). Due to fast internal conversion and intramolecular vibrational redistribution, photoexcitation leads to the formation of temporary negative ions (TNIs), the same as those one formed by the electron attachment. Absolute vibrational autodetachment and recurrent (or Poincaré) fluorescence (RF) rate coefficients have already been reported [V. Chandrasekaran et al., J. Phys. Chem. Lett. 5, 4078 (2014)]. Knowing the branching ratios of the various competing rate coefficients is decisive to the understanding of the formation probability of anions via REA. The radiative stabilization rate of C6−, shown to be dominated by RF, was determined to be 5 × 104 s−1 at the electron detachment energy, i.e., at least a factor of 100 faster than the stabilization by infrared transitions. The RF is found to very effectively stabilize the TNI formed by electron attachment. Using detailed balance to link the measured delayed detachment rate to the rate of electron attachment, we estimate the REA rate leading to the formation of C6− to be 3 × 10−7 cm3 s−1 at 300 K in agreement with theory (1.7 × 10−7 cm3 s−1 [R. Terzieva and E. Herbst, Int. J. Mass Spectrom. 201, 135 (2000)]). Such a high rate for REA to C6 indicates that REA may play a prominent role in the formation of anions in the interstellar medium.

Effect of a localized charge on the stability of Van der Waals clusters

The stability of anionic (SF 6)- N clusters (in the range of N< 23), generated in a supersonic expansion ion source with electron impact ionization, was investigated by measuring their blackbody induced radiative dissociation (BIRD) rates in an electrostatic ion beam trap (EIBT) at room temperature. The lifetime traces of EIBT-stored clusters were subjected to “master equation analysis” and the activation energies, E a , for the evaporation of a S F 6 monomer were extracted. We find that the decay rates of (SF 6)- N anionic clusters are larger than those of cationic SF + 5(SF 6)N-1 measured previously by the same method, and their corresponding activation energies to be smaller. These observations provide further insight into the effect of localized charge on cluster stability.

Observation of longitudinal quadrupole ion bunch oscillations in an electrostatic ion beam trap.

Ions in an ion bunch trapped inside an Electrostatic Ion Beam Trap (EIBT) exhibit collective oscillations within the bunch under the influence of an external driving force. These internal oscillations have been measured explicitly using a new method with a particle detector outside the EIBT. In this approach, the evolving ion bunch is monitored along the entire trap length, in contrast to the localized single point measurements that are often carried out in other techniques. In the present study, quadrupole oscillations have been measured for the first time in an EIBT along with the dipole oscillations that were measured previously. The frequency of the quadrupole oscillation is found to be about twice the dipole oscillation frequency. This is in agreement with the prediction of a theoretical model.

Decay processes and radiative cooling of small anionic copper clusters

The decay of copper clusters ${\mathrm{Cu}}_{n}^{\ensuremath{-}}$ with size $n=4\ensuremath{-}7$, produced in a metal ion sputter source, was studied in an electrostatic ion-beam trap. The neutral products after electron emission and fragmentation were monitored for ion storage times of up to a second. The observations indicated the presence of radiative cooling. The energy distributions of the remaining clusters were probed by laser irradiation up to several further seconds of storage time. This defined excitation lead to photoinduced decay signals which, again, showed signs of radiative cooling for ${\mathrm{Cu}}_{6,7}^{\ensuremath{-}}$, not, however, for ${\mathrm{Cu}}_{4,5}^{\ensuremath{-}}$.

Near-Threshold Photodetachment Cross Section of (SF6)(n)(-) Cluster Anions: The Ion Core Structure.

Photodetachment cross sections as a function of photon energy are measured for cold (SF6)n(-) cluster anions stored in an electrostatic ion beam trap. Absolute photodetachment cross sections near the adiabatic limit are reported. The strong dependence of the SF6(-) absolute photodetachment cross section on the anion equilibrium bond length leads to the conclusion that the excess charge is localized on a SF6(-) ion core that is only subtly perturbed by the neighboring cluster units.

An Electrostatic Ion Beam Trap Technique and Its Application

An Electrostatic Ion Beam Trap Technique and Its Application

Spreading times of ion-bunches in the Cryogenic Trap for Fast ion beams

The decay of ion-bunches stored in the self-bunching mode of an electrostatic ion beam trap (EIBT) has been investigated as a function of the number of injected ions with the Cryogenic Trap for Fast ion beams (CTF) located at the Max Planck Institute for Nuclear Physics in Heidelberg. By use of the pickup-electrode signal the dependence of the characteristic bunch-spreading time τ, i.e. the time in which the bunch width increases by one third, on the number of injected ions is determined. For F− ions with an initial bunch length of 2.7μs the spreading times are observed to increase approximately linearly with the number of injected ions and to reach a constant value of ∼10s for ion numbers larger than 4×105.

Electron detachment and fragmentation of laser-excited rotationally hotAl4−

Absolute photoabsorption cross sections of negatively charged tetra-atomic aluminum clusters have been measured for photon energies between 1.8 and 2.7 eV. The experiment used the depletion technique in combination with an electrostatic ion-beam trap, in which ${{\mathrm{Al}}_{4}}^{\ensuremath{-}}$ ions produced in a sputter ion source were stored for 90 ms before being subjected to a short laser pulse. Moreover, the competition between one-atom fragmentation and electron emission of the laser-excited ${{\mathrm{Al}}_{4}}^{\ensuremath{-}}$ has been measured. These measurements show that fragmentation dominates electron emission at all photon energies below the electron attachment energy of $\ensuremath{\sim}2.2$ eV, even though the fragmentation energy is expected to be 10%--20% higher than the electron attachment energy. These findings, when taken together with the delayed-electron and fragmentation yields observed in a previous measurement [O. Aviv et al., Phys. Rev. A 83, 023201 (2011)], can be well explained within the statistical phase-space theory for unimolecular decays assuming the ${{\mathrm{Al}}_{4}}^{\ensuremath{-}}$ ions to be rotationally hot. The analysis permits the determination of the adiabatic electron detachment energy of ${{\mathrm{Al}}_{4}}^{\ensuremath{-}}$ to be ${E}_{\text{ad}}=(2.18\ifmmode\pm\else\textpm\fi{}0.02)$ eV and the one-atom fragmentation energy to be ${D}_{0}=(2.34\ifmmode\pm\else\textpm\fi{}0.05)$ eV. Moreover, two direct $s$-wave ionization channels are observed with threshold energies of $(2.18\ifmmode\pm\else\textpm\fi{}0.02)$ eV and $(2.45\ifmmode\pm\else\textpm\fi{}0.02)$ eV.

A VMI setup to study prompt and delayed electron emission from trapped cluster anions

SynopsisWe have designed a velocity map imaging (VMI) setup and integrated it with an Electrostatic Ion Beam Trap (EIBT) to study photon induced prompt and delayed electron emission from trapped cluster anions. The operational details are discussed here. The performance of the VMI is also reported for photoionization of trapped O− ions.

Measuring lifetimes of Polycyclic Aromatic Hydrocarbon fragments

SynopsisWe investigate collisions of Polycyclic Aromatic Hydrocarbon cations with noble gases at center-of- mass energies close to 100 eV and below. Charged fragments are stored in a new version of the electrostatic ion beam trap ConeTrap. After storage for different well-defined times we extract the ions and use a reflectron based time-of-flight mass spectrometer to analyse the ion mass distributions. This will give information on secondary decay channels and the lifetime of the initially trapped fragment.

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We determined absolute rate coefficients for the recurrent fluorescence (RF) process in C6– anions at excitation energies above the adiabatic electron attachment energy of 4.18 eV. The experiment was performed by extracting C6– ions from a sputter ion source and storing them in a bent electrostatic ion beam trap. After 1 s of storage, during which the anions cooled down to temperatures close to room temperature, they were excited by a short laser pulse and the neutralization rate due to vibrational autodetachment (VAD) was measured as a function of time at several wavelengths. Due to the different energy dependence of the two competing decays via the RF and the VAD process, their contributions to the measured total decay rate coefficients could be disentangled. For excitation energies ≲4.6 eV, the decay is found to be dominated by the RF process with decay rate coefficients on the order of 5 × 104 s–1. The result clearly demonstrates the presence of the RF process in C6– and illustrates the importance of ...

Sidebands from longitudinal bunch oscillations in an electrostatic ion beam trap

Sidebands are observed in the Fourier transform of the pickup signal of an RF-bunched beam oscillating in an electrostatic ion beam trap. We show that the sidebands are dominated by a collective longitudinal oscillation of the center of the bunch around the synchronous ion as the bunch travels within the storage device. We present evidence for a linear dependence of the sideband frequency and for a seemingly chaotic behavior of the amplitude of the sideband peaks on the number of stored ions.

Development of an Electrostatic Ion Beam Trap for the Study of Beta Decay Correlations

Development of an Electrostatic Ion Beam Trap for the Study of Beta Decay Correlations