Protonated silanoic acid HSi(OH)2+ and its neutral counterpart: a tandem mass spectrometric and CBS‐QB3 computational study Journal Articles uri icon

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abstract

  • AbstractProtonated silanoic acid, HSi(OH)2+, 1a+, is cleanly generated by the dissociative electron ionization of triethoxysilane, HSi(OC2H5)3, and tetraethoxysilane, Si(OC2H5)4. This follows from tandem mass spectrometric experiments and CBS‐QB3 model chemistry calculations. The calculations predict that 1a+ (ΔHf(298 K) = 205 kJ mol−1) is separated by high barriers from its isomers HOSiOH2+, 1b+ and HSi(O)OH2+, 1c+. Low‐energy (metastable) ions 1a+ dissociate by loss of H2O via the pathway 1a+ → 1b+ → SiOH+ + H2O. Analysis of the metastable peak for this process confirms that the isomerization step 1a+ → 1b+ is rate determining. The calculations further predict that the incipient ions 1b+ communicate via a low barrier with the proton‐bound dimer SiO···H···OH2+, 1d+. This dimer ion is much lower in energy than its counterpart OSi···H···OH2+, 1e+, which is calculated to be only marginally stable. A comparison of the potential energy diagram for the silicon‐containing ions 1a+–1e+ with that of their carbon analogues reveals that the dissociation chemistries of HSi(OH)2+ and HC(OH)2+ are only superficially similar. Neutralization–reionization experiments confirm the theoretical prediction that the HSi(OH)2• radical (ΔHf(298 K) = −455 kJ mol−1) is a stable species in the rarefied gas phase. However, owing to a mismatch of Franck–Condon factors a large fraction of the neutralized ions dissociates by loss of H• yielding Si(OH)2. Copyright © 2004 John Wiley & Sons, Ltd.

authors

  • Srikanth, R
  • Bhanuprakash, K
  • Srinivas, R
  • Wong, Cathy Y
  • Terlouw, Johan

publication date

  • March 2004