A bent electrostatic ion beam trap for simultaneous measurements of fragmentation and ionization of cluster ions

Abstract

We describe a bent electrostatic ion beam trap in which cluster ions of several keV kinetic energy can be stored on a V-shaped trajectory by means of an electrostatic deflector placed between two electrostatic mirrors. While maintaining all the advantages of its linear counterpart [Zajfman et al., Phys. Rev. A 55, R1577 (1997); Dahan et al., Rev. Sci. Instrum. 69, 76 (1998)], such as long storage times, straight segments, and a field-free region for merged or crossed beam experiments, the bent trap allows for simultaneous measurement of charged and neutral fragments and determination of the average kinetic energy released in the fragmentation. These unique properties of the bent trap are illustrated by first results concerning the competition between delayed fragmentation and ionization of Al(n) (-) clusters after irradiation by a short laser pulse.

Short pulse laser-induced dissociation of vibrationally cold, trapped molecular ions

“…These might include: installing a position sensitive detector to image the reaction products (Pavičić et al 2005, Wang et al 2006; studying ionic fragments by pulsing the trap potentials allowing them to remain trapped (Stochkel et al 2008) or ejecting them using a trap with a bent geometry (Aviv et al 2008); improving the ToF resolution by reducing the energy spread in the ions, either directly from the ion source or by phase space manipulation of the ions while trapped (Goldberg et al 2003).…”

Competition between delayed ionization and fragmentation of laser-excited Al4−

“…A detailed description of the experimental setup was recently published [13]. Briefly, negatively charged aluminum clusters are produced in a cesium sputter source and are accelerated to a kinetic energy of 4.2 keV.…”

“…[8] and the large calculated fragmentation thresholds, delayed monomer and, even more so, delayed dimer fragmentation were expected to be negligible at photon energies < ∼ 2 eV as compared to delayed electron emission. It therefore came as a surprise that in a follow-up experiment performed with a modified electrostatic ion beam trap (EIBT) [13], which allows to measure simultaneously delayed electron emission (a) and one-atom fragmentation (b), the branching ratio for monomer fragmentation was actually found to be ∼10%. Alerted by this unexpected observation, we have recently searched for the even less likely dimer (c) and trimer (d) emissions after laser excitation using the ELectrostatic Ion Storage ring in Aarhus (ELISA) [14]; under similar experimental conditions, however, the branching ratios of both channels were found to be less than 0.1% of the monomer channel.…”

“…To get more insight into the origin of the unexpected large fraction of delayed monomer emission, a systematic investigation of the competition between delayed fragmentation and electron emission of laser-excited Al − 4 clusters was performed using a bent EIBT [13]. Delayed electron emission and delayed monomer fragmentation have been measured simultaneously as a function of photon energy and cluster temperature for ∼200 µs after the laser pulse.…”

Dissociative recombination and mutual neutralization of heavier molecular ions: C10H8+, WF5+, and CnFm+

“…1 The upper mass limit in magnetic rings, however, is approximately 100 Da, due to the fact that heavier ions have lower velocities for stable orbits and then achieving velocity-matching conditions is extremely difficult. 8 The more recent electrostatic ion storage rings 1, [9][10][11] and traps [12][13][14] can overcome the mass limit because they do not fight the velocitydependent Lorentz force, but only a handful of DR (and no MN) measurements have been taken with these relatively new apparatuses. 9,15 Additional electrostatic storage rings and a) E-mail: afrl.rvborgmailbox@kirtland.af.mil traps are currently being developed.…”