Thermochemical stabilities and structures of the cluster ions OCS+, S2+, H+(OCS), and C2H5+ with OCS molecules in the gas phase

• Published in: Journal of the American Society for Mass Spectrometry 2005-11, Vol.16 (11), p.1760-1771
• Main Authors: Hiraoka, K, Fujita, K, Ishida, M, Hiizumi, K, Nakagawa, F, Wada, A, Yamabe, S, Tsuchida, N
• Format: Article
• Language: English
• Subjects: Bond energy; Carbonyls; Chemical bonds; Clustering; Clusters; Covalence; Density functional theory; Electron beams; Gases - analysis; Gases - chemistry; Hydrogen - analysis; Hydrogen - chemistry; Ions; Isomerization; Isomers; Mass spectrometry; Mathematical analysis; Phase Transition; Spectrometry, Mass, Electrospray Ionization - methods; Sulfur - analysis; Sulfur - chemistry; Sulfur Oxides - analysis; Sulfur Oxides - chemistry; Temperature; Thermal energy
• ISSN: 1044-0305; 1879-1123
• DOI: 10.1016/j.jasms.2005.07.007

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.