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 Title: Chirped-pulse Broadband Microwave Spectra And Structures Of The Ocs Trimer And Tetramer Author(s): Seifert, Nathan A Contributor(s): McKellar, Bob; Moazzen-Ahmadi, Nasser; Dehghany, Mehdi; Pate, Brooks; Perez, Cristobal; Evangelisti, Luca Subject(s): Clusters/Complexes Abstract: Structure determination of weakly bound OCS clusters is a challenging problem due to many low energy isomers on the potential energy surface. The premier tool for studying these clusters is high-resolution infrared spectroscopy, as it can be used to analyze non-polar clusters. Following the analysis of high-resolution IR spectra of clusters formed in a molecular beam expansion of OCS there were some outstanding questions about the structures of the observed clusters. The chirped-pulse Fourier transform microwave spectrum in the 3-9 GHz frequency range was measured for a pulsed molecular beam of OCS in neon (1\%). All $^{13}$C, $^{18}$O and $^{34}$S isotopologues of the previously detected OCS trimer have been observed in natural abundance in the 3-9 GHz band using chirped-pulse Fourier transform microwave spectroscopy. The structure of this trimer features a barrel-shaped structure with two aligned and one anti-aligned OCS monomers. A new OCS trimer is also observed for the first time, and its structure is consistent with a barrel-shaped structure with 3 aligned monomers. Using the infrared spectrum for guidance, a spectrum corresponding to a polar OCS tetramer has been assigned. This cluster has a similar barrel-like structure but with an additional tilted OCS monomer added to the top of the barrel. All $^{13}$C and $^{34}$S isotopologues have been assigned for the tetramer. However, due to sign ambiguities in Kraitchman's equations, and small rotational constant differences between aligned and anti-aligned combinations of OCS molecules in the trimer barrel, absolute structural assignment is indeterminate without additional constraints. Therefore a combinatoric approach was used to compute the most reasonable tetramer structure using distance and sign constraints between pairs of carbon and sulfur coordinates, assuming the experimental OCS monomer structure. Results of this approach will be presented, as well as a comparison of the experimental results with the most recent ab initio structures for the OCS tetramer. Issue Date: 2014-06-20 Publisher: International Symposium on Molecular Spectroscopy Citation Info: Seifert, N.A.; McKellar, B.; Moazzen-Ahmadi, N.; Dehghany, M.; Pate, B.; Perez, C.; Evangelisti, L. CHIRPED-PULSE BROADBAND MICROWAVE SPECTRA AND STRUCTURES OF THE OCS TRIMER AND TETRAMER. Proceedings of the International Symposium on Molecular Spectroscopy, Urbana, IL, June 16-21, 2014. DOI: 10.15278/isms.2014.FB10 Genre: CONFERENCE PAPER/PRESENTATION Type: Text Language: English URI: http://hdl.handle.net/2142/51072 DOI: 10.15278/isms.2014.FB10 Rights Information: Copyright 2014 by the authors. Licensed under a Creative Commons Attribution 4.0 International License. http://creativecommons.org/licenses/by/4.0/ Date Available in IDEALS: 2014-09-172015-04-14
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