Decays of excited silver-cluster anions Agn , n=4 to 7, in the Double ElectroStatic Ion Ring ExpEriment

Abstract

Spontaneous decays of small, hot silver cluster anions Ag − n n = 4 − 7 have been studied using one of the rings of the Double ElectroStatic Ion Ring ExpEriment (DESIREE). Observation of these decays over very long time scales is possible due to the very low residual gas pressure (∼ 10 −14 ) and cryogenic (13 K) operation of DESIREE. The yield of neutral particles from stored beams of Ag − 6 and Ag − 7 anions were measured for 100 milliseconds and were found to follow single power law behaviour with millisecond time scale exponential cut-offs. The Ag − 4 and Ag − 5 anions were stored for 60 seconds and the observed decays show two-component power law behaviors. We present calculations of the rate constants for electron detachment from, and fragmentation of Ag − 4 and Ag − 5 . In these calculations, we assume that the internal energy distribution of the clusters are flat and with this we reproduce the early steep parts of the experimentally measured decay curves for Ag − 4 and Ag − 5 , which extends to tens and hundreds of milliseconds, respectively. The fact that the calculations reproduce the early slopes of Ag − 4 and Ag − 5 , which differ for the two cases, suggests that it is the changes in fragmentation rates with internal cluster energies of Ag − 4 and Ag − 5 rather than conditions in the ion source that determines this behavior. Comparisons with the measurements strongly suggest that the neutral particles detected in these time domains originate from Ag − 4 →Ag − 3 + Ag and Ag − 5 →Ag − 3 + Ag2 fragmentation processes. arXiv:1805.12437v1 [physics.atm-clus] 31 May 2018

Radiative cooling of carbon cluster anions C2n+1− (n = 3–5)

“…Transport from the source to the ring takes ≈80−100 µs and the 1/e beam storage lifetimes are typically >100 s, limited by loss of ions through collisions with background gas of ∼10 4 H 2 molecules per cm 3 [28,31]. The ions initially stored in the ring have a broad distribution of internal excitations, similar to thermal distributions with temperatures exceeding 1000 K [26]. Ions with internal energies exceeding the adiabatic detachment energy may spontaneously neutralize via thermionic emission.…”

“…emission due to decay of thermally populated electronically exicted states. The advent of a new generation of cryogenically cooled electrostatic storage devices has extended the time range for observations of spontaneous neutralization to several seconds [24][25][26][27].…”

Radiative cooling of size-selected gas phase clusters

“…Storage ring experiments on radiative cooling of metal clusters have focused on anions. At present aluminium [56,64,112,113], copper [114][115][116], and silver [56,117] have been studied. The clusters tend to be small, due to the characteristics of the frequently used cesium sputter sources.…”

Ultraslow radiative cooling of Cn− (n = 3–5)

“…19,27 Cooling dynamics in this regime have been explored for only a few small anions due to technical challenges associated with isolating ions for durations extending to minutes and maintaining low background temperatures. [28][29][30][31][32][33] While the target anions have been intensively studied by several groups in recent years, all studies used room-temperature electrostatic ion storage rings or beam traps and were limited to characterizing cooling dynamics occurring on sub-second timescales. 23,25,[34][35][36][37] In the present study, we have used the DESIREE infrastructure to investigate the cooling dynamics of the target anions on the ultraslow, t > ∼ 1 s timescale.…”