Radiative cooling of ${\rm C}_7^-$C7−

Abstract

The spontaneous and photo-induced neutralization of C₇⁻ produced in a laser ablation source was measured in an electrostatic storage ring. The measurements provide three independent determinations of the radiative cooling of the ions, based on the short time spontaneous decay and on the integrated amplitude and the shape of the photo-induced neutralization signal. The amplitude of the photo-induced signal was measured between 0.5 ms and 35 ms and found to depend on photon wavelength and ion storage time. All three signals can be reproduced with identical thermal IR radiative cooling rates with oscillator strengths equal to theoretical predictions. In addition, the measurements provide the excitation energy distribution.

Long-Term Monitoring of the Internal Energy Distribution of Isolated Cluster Systems

“…A prompt spike comprizes neutralization within ∼T /4 after illumination. Then, similar to earlier experiments [9,10], spikes delayed by τ = nT /2 (integer n) follow from anions performing n half-roundtrips before electron emission. The spikes of R(τ ) integrate delayed electron emission events that clusters undergo during τ ± T /4.…”

“…Recently, ion-trap experiments could access internal energy relaxation through studies of delayed electron emission from molecular and cluster anions. Timeresolved measurements indirectly demonstrated Stefan-Boltzmann-like relaxation [8] and sampled shifts of internal energy distributions for up to ∼100 ms [9,10]. Yet, basic uncertainties remain: Without direct scanning of the internal energy distribution (IED) in a cluster ensemble it is unclear how closely the IEDs follow a canonical shape.…”

Thermal radiation of gold clusters on microsecond time scales

“…The precise time dependence is determined by the energy of the emitted photons relative to an energy scale determined by the (microcanonical) temperature, the heat capacity, and the evaporative activation energy [9,23]. For the energy of the photons expected to describe the behavior observed here, a single rate constant, k p , gives the suppression directly (the continuous cooling approximation requires photon energies below 220 meV for n = 15; see [23]). The decay rate relevant here is then…”

Cooling dynamics of photo-excited negative carbon cluster ions stored in an ion storage ring

“…Conversely, if the population of the anions with a specific rate constant is determined, the energy distribution is obtained from the function of k d ðEÞ. On the basis of this assumption, we have measured the radiative cooling rates of C À 5 and C À 7 [4,5]. Relevant experiments were conducted using an electrostatic ion storage ring at Tokyo Metropolitan University (TMU E-ring).…”

“…The fast cooling originates in the presence of low-lying electronically excited states. It is considered to be a common feature of the small even-numbered carbon cluster anions, whereas the cooling of odd-numbered clusters (C À 5 and C À 7 ) is as slow as polyyne anions [4,5].…”