Radiative cooling of size-selected gas phase clusters

Abstract

Predicted almost forty years ago, the radiation from thermally populated excited electronic states has recently been recognized as an important cooling mechanism in free molecules and clusters. It has presently been observed from both inorganic clusters and carbon-based molecules in molecular beams and ion storage devices. Experiments have demonstrated that many of these systems radiate at rates approaching microsecond time scales, and often with a distinct dependence on the precise number of atoms in the system. The radiation acts as a strongly stabilizing factor against both unimolecular decay and thermal electron emission. In astrophysical context, radiative cooling provides a mechanism to dissipate internal energy in star-forming processes, and stabilizes molecules selectively in the circumstellar medium. The consequences of an active radiative cooling channel for nanoparticle production will likewise favor special sizes in nonequilibrium formation processes. In this review, the radiative cooling of clusters is presented and illustrated with examples of experiments performed on small carbon, metal, and semiconductor clusters, and on PAH molecules. The experimental and theoretical techniques used are discussed, together with the consequences of radiative cooling on size-to-size stability patterns of clusters.

Roadmap on dynamics of molecules and clusters in the gas phase

“…Another channel for which the power law has provided a very powerful diagnostic tool is the thermal photon emission [229,230]. Radiative cooling will modify the power law decay by suppressing it at long times with an exponential factor.…”

Gas-phase studies of the retinal protonated Schiff base chromophore

“…As this process is statistical in nature, it can be use to study statistical properties of isolated ions. Indeed, statistical dissociation has been used as a temperature gauge when studying radiative cooling of various ions [51,52]. In a 2012 work, Toker et al [53] have measured the heat capacity of the RPSB using delayed dissociation.…”

Decay Dynamics in Molecular Beams

“…The details of the description of this suppression depend on the magnitude of the emitted photons. The systematics of this behavior is summarized in a recent review article (Ferrari et al, 2019), and only a few points concerning the influence of thermal radiation on decay rates will be taken up here. For sufficiently small photon energies, emission of a single photon is insufficient to cause a major change in the unimolecular rate constant.…”

“…Here only the small photon energy limit will be discussed. The large photon limit is treated in (Ferrari et al, 2019).…”