Spectroscopy of free radicals and radical containing entrance-channel complexes in superfluid helium nanodroplets

Abstract

The spectroscopy of free radicals and radical containing entrance-channel complexes embedded in superfluid helium nano-droplets is reviewed. The collection of dopants inside individual droplets in the beam represents a micro-canonical ensemble, and as such each droplet may be considered an isolated cryo-reactor. The unique properties of the droplets, namely their low temperature (0.4 K) and fast cooling rates (∼ 10 16 K s −1 ) provides novel opportunities for the formation and high-resolution studies of molecular complexes containing one or more free radicals. The production methods of radicals are discussed in light of their applicability for embedding the radicals in helium droplets. The spectroscopic studies performed to date on molecular radicals and on entrance / exitchannel complexes of radicals with stable molecules are detailed. The observed complexes provide new information on the potential energy surfaces of several fundamental chemical reactions and on the intermolecular interactions present in open-shell systems. Prospects of further experiments of radicals embedded in helium droplets are discussed, especially the possibilities to prepare and study high-energy structures and their controlled manipulation, as well as the possibility of fundamental physics experiments.

IR Spectroscopic Characterization of the Thermally Induced Isomerization in Carbon Disulfide Dimer Anions

“…The present results demonstrate how vibrational spectroscopy can be used to track a thermally induced intramolecular reaction from the entrance channel complex to a covalently bound product in order to ultimately gain a better understanding of the influence of long-range dispersion forces on molecular reactions dynamics. [19][20][21] The (CS 2 ) 2 system is particularly intriguing in that the barrier toward isomerization lies below the energy of the reactants, and thus, it represents an interesting model system for timeresolved studies aimed at unraveling the dynamics of internal conversion.…”

Chemistry and physics of dopants embedded in helium droplets

“…This shrinking of the droplets leads to a reduction of the ionization cross‐section and a depletion of the ion yield of low‐mass ions that serve as a messenger for the absorption of a photon by the dopant. Several reviews are specially dedicated to spectroscopy of neutral and radical dopants in HNDs (Callegari et al, 2001; Choi et al, 2006; Higgins et al, 2000; Kuyanov‐Prozument et al, 2011; Küpper & Merritt, 2007; Stienkemeier & Lehmann, 2006; Verma et al, 2019) to which we refer here the interested reader.…”

Reactions of Photoionization-Induced CO–H2O Cluster: Direct Ab Initio Molecular Dynamics Study

“…Therefore, it is possible to perform high-resolution spectroscopy of molecules in helium droplets. 7 − 10 …”