title: Thermochemical stabilities and structures of the cluster ions OCS+, S2+, H+(OCS), and C2H5+ with OCS molecules in the gas phase.
abstract: The gas-phase clustering reactions of OCS+, S2+, H+(OCS), and C2H5+ ions with carbonyl sulfide (OCS) molecules were studied using a pulsed electron-beam high-pressure mass spectrometer and applying density functional theory (DFT) calculations. In the cluster ions OCS+(OCS)(n) and H+(OCS)(OCS)(n), a moderately strong, here referred to as "semi-covalent", bond was formed with n = 1. However, the nature of bonding changed from semi-covalent to electrostatic with n = 1 --> 2. The bond energy of S2(+)(OCS) was determined experimentally to be 12.9 +/- 1 kcal/mol, which is significantly smaller than that of the isovalent S2(+)(CS2) complex (30.9 +/- 1.5 kcal/mol). DFT based calculations predicted the presence of several isomeric structures for H+(OCS)(OCS)(n) complexes. The bond energies in the C2H5+(OCS)(n) clusters showed an irregular decrease for n = 1 --> 2 and 7 --> 8. The nonclassical bridge structure for the free C2H5+ isomerized to form a semi-covalent bond with one OCS ligand, [H3CCH2...SCO]+, i.e., reverted to classical structure. However, the nonclassical bridge structure of C2H5+ was preserved in the cluster ions C2H5+(OCS)(n) below 140 K attributable to the lack of thermal energy for the isomerization. DFT calculations revealed that stability orders of the geometric isomers of H+(OCS)(OCS)(n) and C2H5+(OCS)(n) changed with increasing n values.
authors.affiliation: Clean Energy Research Center, University of Yamanashi, Takeda 4-3-11, Kofu 400-8511, Japan. hiraoka@ab11.yamanashi.ac.jp
authors.forename: K
authors.initials: K
authors.lastname: Hiraoka
authors.forename: K
authors.initials: K
authors.lastname: Fujita
authors.forename: M
authors.initials: M
authors.lastname: Ishida
authors.forename: K
authors.initials: K
authors.lastname: Hiizumi
authors.forename: F
authors.initials: F
authors.lastname: Nakagawa
authors.forename: A
authors.initials: A
authors.lastname: Wada
authors.forename: S
authors.initials: S
authors.lastname: Yamabe
authors.forename: N
authors.initials: N
authors.lastname: Tsuchida
mesh_terms: D005740:Gases / Q000032:analysis / Q000737:chemistry*; D006859:Hydrogen / Q000032:analysis / Q000737:chemistry; D007477:Ions; D044367:Phase Transition; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D013455:Sulfur / Q000032:analysis / Q000737:chemistry; D013461:Sulfur Oxides / Q000032:analysis* / Q000737:chemistry*; D013696:Temperature
chemical_list: D005740:Gases; D007477:Ions; D013461:Sulfur Oxides; D013455:Sulfur; D006859:Hydrogen; C010063:carbonyl sulfide