Infrared spectrum of the silicon hydride cation SiH7+

Abstract

Silanium ions are an important class of hypervalent molecules, and the determination of their structure will yield insights into the nature of nonclassical bonding and provide a contrast to the bonding in carbonium ions. We report the infrared spectrum of the mass-selected silicon hydride cluster ion 28SiH7, detected by vibrational predissociation spectroscopy. Silanium ions were foimed in a pulsed high pressure glow discharge and cooled by the subsequent supersonic expansion. Photodissociation spectra were obtained using a tandem time-of-flight mass spectrometer: SiH7 ions were mass-selected and excited by a tunable infrared laser. The resulting photofragments were detected using a reflectron as a mass analyzer. We observed a vibrational band at 3865 cm1, which was the only one observed from 3500 cm1 to 4200 cm1. This result suggests that the molecule might form a symmetric complex with the structure H2 SiH3H2, in contrast to the species CH7, which has the structure CH5H2.

Infrared spectrum of the disilane cation (Si2H6+) from Ar-tagging spectroscopy

“…40,41 The 12 vibrational fundamentals of Si 2 H 6 , n [1][2][3][4][5][6][7][8][9][10][11][12] , transform in D 3d as G vib = 3a 1g + a 1u + 2a 2u + 3e u + 3e g . We follow the notation of vibrational modes given previously in ref.…”

Silicenium Ions: Quantum Chemical Computations

“…This viewpoint was challenged by Olah and coworkers, who regard such species as halonium ions 74,89 . The infrared (IR) spectrum of SiH 7 C (22), formally a complex of H 3 Si C and two molecules of H 2 , was reported in 1993 by Okumura and coworkers 93 . The IR spectrum displayed a single band centred around 3866 cm 1 , which was red-shifted by 295 cm 1 with respect to free molecular hydrogen 93 .…”

“…The infrared (IR) spectrum of SiH 7 C (22), formally a complex of H 3 Si C and two molecules of H 2 , was reported in 1993 by Okumura and coworkers 93 . The IR spectrum displayed a single band centred around 3866 cm 1 , which was red-shifted by 295 cm 1 with respect to free molecular hydrogen 93 . The absence of a second band in the 3500 to 4200 cm 1 region suggested a symmetric complex with the structure H 2 SiH 3 C H 2 , i.e.…”

“…The absence of a second band in the 3500 to 4200 cm 1 region suggested a symmetric complex with the structure H 2 SiH 3 C H 2 , i.e. a planar SiH 3 C species with two equidistant H 2 ligands bound to opposite faces of the silicenium ion 93 . Moreover, the authors suggested a preferred side-on ligation of the H 2 moieties, since such an arrangement would maximize the electron donation from the H H bonds into the empty 3p-orbital on silicon 93 .…”

“…a planar SiH 3 C species with two equidistant H 2 ligands bound to opposite faces of the silicenium ion 93 . Moreover, the authors suggested a preferred side-on ligation of the H 2 moieties, since such an arrangement would maximize the electron donation from the H H bonds into the empty 3p-orbital on silicon 93 . Based on an empirical correlation between the lowering of the H H stretching mode and the binding energy of molecular hydrogen ion cluster complexes, a crude binding energy estimate of 7 9 kcal mol 1 was obtained 93 .…”