The first spectroscopic evidence of a double-bridged silicon molecule is reported. The submillimeterwave rotational spectrum of the disilyne S12H2 has been observed in a low-power silane plasma cooled at liquid-nitrogen temperature, with argon as buffer gas. These measurements led to the determination of the ro structure, which is in good agreement with ab initio calculations. This nonclassical structure is confirmed by the observation of the 29 Si and 30 Si monosubstituted forms.PACS numbers: 33.10.Ev, 33.20.Bx, 35.20.Dp, 35.20.Pa There is presently a growing interest in the study of small unsaturated silicon compounds, related to the vapor deposition of amorphous silicon films. 1 " 3 Detection of some monosilicon intermediate species [SiH" (Ref. 4); SiH" + (Ref. 5), n<3] by high-resolution spectroscopy has already led to the development of nonintrusive diagnostic techniques of silane plasmas. 2,3,6 In contrast, experimental data on unsaturated disilicon hydrides are very scarce, although recent mass-spectrometry investigations 7 have shown that Si2H2 and Si2H4 can be abundant in SiH4 plasmas and therefore can play a key role in deposition processes (Refs. 1-3, and 8, and references therein).The study of these highly reactive species also has its own interest, for a fundamental comparison between carbon and silicon bonding properties. For example, ab initio calculations have shown that the simplest unsaturated hydrides SiiFh and Si2H4 exhibit geometries very different from the analogous C-containing molecules, and that the smaller basis sets are not adequate to properly describe the structures and the relative stabilities of the various isomers. 9 " 15 In particular, it has been shown that addition of Si d functions and of electron correlation makes the nonclassical bridged structure of the disilyne Si(H2)Si in its singlet ground state more stable than the silasilene F^SiSi classical structure, which is the minimum-energy structure at the HF/3-21G level. 14 The energy difference between the two structures is rather small, in the range of 7-13 kcal/mol. 9 " 12,14 In fact, bridged structures are well known in molecules involving electron-deficient atoms such as boron. 16 Nevertheless, very little is experimentally known regarding the existence of such three-center bonds in the group-IV compounds. Protonated acetylene, recently investigated by ir spectroscopy 17 and Coulomb-explosion experiments, 18 is the only example of such a situation. The nonclassical bridged form HC(H)CH + is calculated to be lower in energy than the classical form F^CCH* by about 4-7 kcal/mol, 19,20 which is consistent with the experiments. However, no complete structural information on C2H3 -1 " can be deduced from these experiments at the moment.In this Letter, we present the first spectroscopic evidence of the disilyne Si2H2, and the first determination of a bridged structure for a silicon-containing molecule.In the course of an investigation of a silane plasma by submillimeter-wave spectroscopy, some unidentified lines were observed a...

A monobridged isomer of the disilyne Si2H2, the planar bridged-2 form Si(H)SiH, has been detected through its millimeter- and submillimeter-wave rotational spectrum. The molecules are produced in a low pressure, low power plasma in a mixture of SiH4 and Ar cooled at liquid nitrogen temperature. From the analysis of a total of 148 lines, a set of accurate rotational constants have been derived. Using the geometry predicted by ab initio calculations (see the preceding paper), the spectrum of Si(D)SiD has been predicted, observed, and analyzed. From the two sets of rotational constants, a preliminary molecular structure has been derived by fixing the Si1–Si2–bridged H angle to the ab initio value of 52.5°: Si1–Si2=2.119 Å; Si2–bridged H=1.629 Å; Si2–terminal H=1.474 Å; Si1–Si2–terminal H=157.5°.

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The millimeter and submillimeter wave spectra of different HID isotopomers of ArH3+ were investigated. The ionic clusters were produced inside a negative glow extended by a magnetic field, in Ar/H2/D2 mixtures. Most of the observed rotational lines were split by internal motion and spin statistical weights as well as intensity ratios for the components were determined from symmetry considerations. The splittings were interpreted in terms of internal motion of the H3+ triangle. In a first step, the usual rigid top-rigid frame model was used to reproduce the order of magnitude of the splittings. In a second step, a more refined model, which accounts for the flexibility of the top and the frame, led to a better calculation of the observed splittings in ArH3+ and ArD3+ .

Articles you may be interested inDistortion of ethyne on coordination to silver acetylide, C2H2AgCCH, characterised by broadband rotational spectroscopy and ab initio calculations Distortion of ethyne on formation of a π complex with silver chloride: C2H2Ag-Cl characterised by rotational spectroscopy and ab initio calculations Millimeter-wave spectroscopy and coupled cluster calculations for a new phosphorus-carbon chain: HC 5 P Silene, H 2 CSiH 2 , has been efficiently produced by pyrolysis of 5,6-bis͑trifluoromethyl͒-2-silabicyclo͓2.2.2͔octa-5,7-diene ͑SBO͒. Seven isotopomers have been observed by millimeterand submillimeter-wave spectroscopy. From the different sets of experimental molecular parameters and from ab initio calculations of the rovibrational interaction parameters, the equilibrium structure has been obtained by a least squares analysis of the rotational constants. The results are: r e (SivC) ϭ 1.7039(18) Å, r e (C-H) ϭ 1.0819(12) Å, r e (Si-H) ϭ 1.4671(9) Å, ЄHCSi ϭ 122.00(4)°, and ЄHSiC ϭ 122.39(3)°. This experimental structure is in excellent agreement with the equilibrium geometry calculated at the CCSD͑T͒ level of theory with a cc-pV͑Q,T͒Z basis set. This is the first experimental determination without any constraint of the SivC double bond length in the parent compound of the silaalkene family. A lifetime of 30 ms has been observed for this molecule in the gas phase at low pressure.