Photoionization mass spectrometric studies of SiHn (n=1–4)

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Abstract
A photoionization mass spectrometric study of SiH4 at T=150 K reveals the presence of SiH+4 with an adiabatic threshold at 11.00±0.02 eV. The implications for the structure of this Jahn–Teller split state are discussed. The appearance potentials of SiH+2 and SiH+3 are 11.54±0.01 eV and ≤12.086 eV, respectively. The reaction of F atoms with SiH4 generates SiH3 (X 2A1), SiH2 (X 1A1 and a 3B1), and SiH (X 2Π) in sufficient abundance for photoionization studies. The measured adiabatic ionization potentials (eV) are: SiH3, 8.01±0.02; SiH2 (X 1A1), 9.15±0.02 or 9.02±0.02; SiH2 (a 3B1), 8.244±0.025; SiH, 7.91±0.01. The singlet–triplet splitting in SiH2 is either 0.78±0.03 or 0.91±0.03 eV. The dissociation energy of SiH is 2.98±0.03 eV. A Rydberg series is observed, converging to SiH+ (a 3Π) at 10.21±0.01 eV. Heats of formation of the various neutral and ionic species are presented, as are the stepwise bond energies of SiH4.