Thermal radiation of gold clusters on microsecond time scales

Abstract

Small positively charged gold clusters have been found to emit thermal radiation at a very high rate, with time constants ranging from one to 35 μs for Au n + (n = 6-13,15). For sizes n = 14,16-20 the radiation occurs on much longer time scales. Strong thermal suppression of the population of higher-lying states puts constraints on the possible energies of excited states that can contribute to the radiation. Taking that into account, an evaluation of the experimentally determined rate constants shows that the strong radiation originates from thermally excited low-lying electronic states hitherto not observed. The origin of these states is discussed and two possibilities are suggested: one is related to electron correlation and electron pairing, and the other results from thermal shape fluctuations.

Radiative cooling of size-selected gas phase clusters

“…The rates of fragmentation and radiation are calculated using input parameters from Refs. [42,43]. The crossing point of the photon emission curve (k rad,RF ) with the dissociation rate constant for dimer emission (k f ) has been determined experimentally.…”

The structures of cationic gold clusters probed by far-infrared spectroscopy

“…Small gold clusters have for decades been a subject of intensive research [1,2,3]. Considering that bulk gold is one of the most unreactive metals in the periodic table, the selective reactivity of gold clusters has drawn particular attention: below a certain critical size, gold clusters are reactive towards CO [4,5] and propene [6], can co-adsorb O2 and CO to form CO2 [7], and can form covalent bonds with noble gases [8].…”

Effect of radiative cooling on the size-dependent stability of small boron clusters

“…Radiative cooling rates of B N + (N = 8 − 20) clusters can be inferred using variable ion extraction times, previously applied in the investigation of laser heated fullerenes [24], niobium [7], silicon [6], and gold [8] clusters. The method is based on the fact that, in the absence of radiation, clusters excited in a broad distribution of energies have fragmentation rates that follow a 1/t dependence in time, with t = 0 the moment of excitation.…”

“…There are two important conclusions about the extracted photon emission rates. First, the very high photon emission rates strongly suggest that decay proceeds via the recurrent fluorescence process, through a thermally populated electronic excited state [8,11]. This process requires the presence of electronically excited states with sufficient oscillator strength and in an appropriate energy window.…”

“…These types of experiments are often analyzed disregarding any cooling channel other than fragmentation. Recent experiments, however, have shown that small carbon and metal clusters can cool radiatively [5][6][7][8][9][10][11], in some cases at very high rates.…”