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A Mass Spectrometry Study of XCO + , X=Si, Ge: Is SiCO + a Main Group Carbonyl? Comments on the Bonding in Ground State SiCO and the [Si,C,O] + Potential Energy Surface
Author(s) -
Jackson Phillip,
Srinivas Ragampeta,
Blanksby Stephen J.,
Schröder Detlef,
Schwarz Helmut
Publication year - 2000
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/(sici)1521-3765(20000403)6:7<1236::aid-chem1236>3.0.co;2-3
Subject(s) - chemistry , ionization , ion , silane , ground state , ionization energy , analytical chemistry (journal) , basis set , mass spectrometry , binding energy , bond energy , carbon monoxide , molecule , crystallography , atomic physics , computational chemistry , density functional theory , physics , biochemistry , organic chemistry , chromatography , catalysis
The cation [Si,C,O] + has been generated by 1) the electron ionisation (EI) of tetramethoxysilane and 2) chemical ionisation (CI) of a mixture of silane and carbon monoxide. Collisional activation (CA) experiments performed for mass‐selected [Si,C,O] + , generated by using both methods, indicate that the structure is not inserted OSiC + ; however, a definitive structural assignment as Si + ‐CO, Si + ‐OC or some cyclic variant is impossible based on these results alone. Neutralisation‐reionisation ( + NR + ) experiments for EI‐generated [Si,C,O] + reveal a small peak corresponding to SiC + , but no detectable SiO + signal, and thus establishes the existence of the Si + ‐CO isomer. CCSD(T)//B3LYP calculations employing a triple‐zeta basis set have been used to explore the doublet and quartet potential‐energy surfaces of the cation, as well as some important neutral states. The results suggest that both Si + ‐CO and Si + ‐OC isomers are feasible; however, the global minimum is 2 Π SiCO + . Isomeric 2 Π SiOC + is 12.1 kcal mol −1 less stable than 2 Π SiCO + , and all quartet isomers are much higher in energy. The corresponding neutrals Si‐CO and Si‐OC are also feasible, but the lowest energy Si‐OC isomer ( 3 A″) is bound by only 1.5 kcal mol −1 . We attribute most, if not all, of the recovery signal in the + NR + experiment to SiCO + survivor ions. The nature of the bonding in the lowest energy isomers of Si + ‐(CO,OC) is interpreted with the aid of natural bond order analyses, and the ground state bonding of SiCO + is discussed in relation to classical analogues such as metal carbonyls and ketenes.