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 Title: THE CO2–(N2)2 AND CO2–Ar2 TRIMERS: INFRARED SPECTRA, STRUCTURAL CALCULATIONS AND INTERMOLECULAR BEND Author(s): Moazzen-Ahmadi, Nasser Contributor(s): McKellar, Bob ; Pietropolli Charmet, Andrea ; Barclay, A. J. Subject(s): Atmospheric science Abstract: The weakly-bound CO$_2$–(N$_2$)$_2$ and CO$_2$-Ar$_2$ trimers have been studied in the carbon dioxide $\nu_3$ asymmetric stretch region ($\sim$2350 cm$^{-1}$). The van der Waals complexes are generated in a supersonic slit-jet apparatus and probed using an optical parametric oscillator. The interaction of N$_2$, the most abundant molecule in the Earth's atmosphere, and CO$_2$ is relevant from the stand point of the overlap of frequencies of the stretching modes of CO$_2$ with the Earth’s emission and its effect on greenhouse. Here, we have observed the fundamental for the CO$_2$–(N$_2$)$_2$ trimer. It is composed of c-type transitions establishing that the trimer has C$_{2v}$ point group symmetry with the CO$_2$ monomer in the ac inertial plane and parallel to the c-axis and the equivalent equatorial N$_2$ monomers in the ab-plane with molecular axes passing through the center of mass of CO$_2$ and making an angle of $64^{\circ}$. Theoretical calculations were performed in support of our observations. Several minima on the PES were found. For the most stable isomer, the vibrational corrections to the equilibrium rotational constants were obtained. The rotational parameters at CCSD(T*)-F12c level of theory gives results in very good agreement with those obtained from the observed vibrational fundamental. Using a dilute mixture of CO$_2$ and Ar in He, we observed a weak b-type combination band involving an intermolecular mode around 2380 cm$^{-1}$. This band is assigned to CO$_2$-Ar$_2$ trimer which also has C$_{2v}$ point group symmetry and a structure similar to CO$_2$–(N$_2$)$_2$ trimer. As such, four of the five combination bands are infrared active. From these only one has b-type transitions which uniquely identifies the intermolecular mode as CO$_2$ bend with an observed frequency of 32.24 cm$^{-1}$. Issue Date: 26-Jun-20 Publisher: International Symposium on Molecular Spectroscopy Citation Info: APS Genre: CONFERENCE PAPER/PRESENTATION Type: Text Language: English URI: http://hdl.handle.net/2142/107496 Date Available in IDEALS: 2020-06-26
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