Observing the Completion of the First Solvation Shell of Carbon Dioxide in Argon from Rotationally Resolved Spectra

Abstract

Widespread interest in weakly bound molecular clusters of medium size (5 ~ 50 molecules) is motivated by their complicated energy landscapes, which lead to hundreds or thousands of distinct isomers. But most studies are theoretical in nature, and there are no experimental results which provide definitive structural information on completion of the first solvation shell. Here we assign rotationally resolved mid-infrared spectra to argon clusters containing a single carbon dioxide molecule, CO2-Ar15 and CO2-Ar17. These mark completion of the first solvation shell for CO2 in argon. The assignments are confirmed by nuclear spin intensity alternation in the spectra, a marker of highly symmetric structures for these clusters. Precise values are determined for rotational parameters, and for shifts of the CO2 vibrational frequency induced by the argon atoms.The spectra indicate possible low frequency (2 cm -1 ) vibrational modes in these clusters, posing a challenge for future cluster theory.

Spectra of CO2‐Kr in the 4.3 μm region: Intermolecular Bend and Symmetry Breaking of the Intramolecular CO2 Bend

“…For an isolated CO 2 molecule the bend is doubly degenerate, but in the dimers it splits into in‐plane (i‐p) and out‐of‐plane (o‐p) components. We have previously reported spectra in the region of the CO 2 ( v 1 , v 2 l 2 , v 3 )=(01 1 1)←(01 1 0) hot band near 2337 cm −1 for CO 2 ‐Ar, [8] −Ne, [9] −Xe, [5] −N 2 [10] and −CO [11] . Transitions from this excited state (01 1 0) to the combination state (01 1 1) exhibit b‐type selection rules, like the ν 3 fundamental.…”