title: Theory vs. experiment for molecular clusters: Spectra of OCS trimers and tetramers.
abstract: All singly substituted (13)C, (18)O, and (34)S isotopomers of the previously known OCS trimer are observed in natural abundance in a broad-band spectrum measured with a chirped-pulse Fourier transform microwave spectrometer. The complete substitution structure thus obtained critically tests (and confirms) the common assumption that monomers tend to retain their free structure in a weakly bound cluster. A new OCS trimer isomer is also observed, and its structure is determined to be barrel-shaped but with the monomers all approximately aligned, in contrast to the original trimer which is barrel-shaped with two monomers aligned and one anti-aligned. An OCS tetramer spectrum is assigned for the first time, and the tetramer structure resembles an original trimer with an OCS monomer added at the end with two sulfur atoms. Infrared spectra observed in the region of the OCS ν1 fundamental (≈2060 cm(-1)) are assigned to the same OCS tetramer, and another infrared band is tentatively assigned to a different tetramer isomer. The experimental results are compared and contrasted with theoretical predictions from the literature and from new cluster calculations which use an accurate OCS pair potential and assume pairwise additivity.
authors.affiliation: Department of Chemistry, University of Virginia, McCormick Road, Charlottesville, Virginia 22904, USA.
authors.forename: Luca
authors.initials: L
authors.lastname: Evangelisti
authors.affiliation: Department of Chemistry, University of Virginia, McCormick Road, Charlottesville, Virginia 22904, USA.
authors.forename: Cristobal
authors.initials: C
authors.lastname: Perez
authors.affiliation: Department of Chemistry, University of Virginia, McCormick Road, Charlottesville, Virginia 22904, USA.
authors.forename: Nathan A
authors.initials: NA
authors.lastname: Seifert
authors.affiliation: Department of Chemistry, University of Virginia, McCormick Road, Charlottesville, Virginia 22904, USA.
authors.forename: Brooks H
authors.initials: BH
authors.lastname: Pate
authors.affiliation: Department of Physics and Astronomy, University of Calgary, 2500 University Drive North West, Calgary, Alberta T2N 1N4, Canada.
authors.forename: M
authors.initials: M
authors.lastname: Dehghany
authors.affiliation: Department of Physics and Astronomy, University of Calgary, 2500 University Drive North West, Calgary, Alberta T2N 1N4, Canada.
authors.forename: N
authors.initials: N
authors.lastname: Moazzen-Ahmadi
authors.affiliation: National Research Council of Canada, Ottawa, Ontario K1A 0R6, Canada.
authors.forename: A R W
authors.initials: AR
authors.lastname: McKellar