Josef Pola

The equilibrium structure of silene H2C=SiH2 from millimeter wave spectra and from ab initio calculations

Silene, H2CSiH2, has been efficiently produced by pyrolysis of 5,6-bis(trifluoromethyl)- 2-silabicyclo[2.2.2]octa-5,7-diene (SBO). Seven isotopomers have been observed by millimeter- and 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: re(Si=C)=1.7039(18) A, re(C–H)=1.0819(12) A, re(Si–H)=1.4671(9) A, ∠HCSi=122.00(4)°, and ∠HSiC=122.39(3)°. This experimental structure is in excellent agreement with the equilibrium geometry calculated at the CCSD(T) level of theory with a cc-pV(Q,T)Z basis set. This is the first experimental determination without any constraint of the Si=C 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.

Laser photolysis of liquid benzene and hexafluorobenzene: Graphitic and polymeric carbon formation at ambient temperature

Abstract ArF laser-induced liquid-phase photolysis of benzene and hexafluorobenzene afford similar products which are polyaromatic hydrocarbons or fluorocarbons with the preponderance of biphenyl or decafluorobiphenyl, graphite, and polymeric H-containing or F-containing carbon. The remarkable feature is that the graphite formation occurs at ambient temperature of the irradiated liquids; photolytic graphitization modes must therefore be different from those occurring in thermally-induced graphitization at temperatures above 2500 °C.

Si/C phases from the IR laser-induced decomposition of silacyclobutane and 1,3-disilacyclobutane

CO 2 laser-induced infrared multiphoton decomposition (IRMPD) and SF 6 photosensitized decomposition (LPD) of silacyclobutane (SCB) and 1,3-disilacyclobutane (DSCB) in the gas phase results in the very efficient deposition of Si/C/H and SiC materials, and it is inferred that the process is dominated by formation of transient silene ; silene rearrangement to methylsilylene ; silene and methylsilylene dehydrogenation ; and polymerization of SiCH n (n < 4) species. The deposits are sensitive to oxygen. Decomposition and SiC formation are favoured with IRMPD experiments conducted with high-energy fluxes. The laser technique is promising for low-temperature chemical vapour deposition of amorphous SiC.

Laser-generated silenes and their gas-phase polymerization

Abstract Infrared and excimer laser-powered decompositions of silacyclobutanes (RH, CH 3 , CH 2 CH and HCC), 4-silaspiro[3,4]octane and 4-silaspiro[3,4]octane and 4-silaspiro[3,3]heptane in the gas phase are shown to be dominated by elimination of ethene to yield transient silenes which efficiently polymerize into solid polycarbosilane deposits, potential precursors to silicon carbide. IR laser powered decomposition of tetramethylcyclotetrasiloxane affords transient hydroxy(methyl)silylene. The organosilicon transients were identified by chemical trapping experiments.

Chemical vapour deposition of germanium films by laser-induced photolysis of ethylgermanes

Excimer laser photolysis of ethylgermanes EtnGeH4–n(n= 1–4) at 193 nm yields ethane, ethene and butane along with germanium deposited on the inner surface of the reactor. The distribution of gaseous products is remarkably different from that produced by thermolysis of ethylgermanes and it is attributed to intramolecular elimination of hydrocarbons. The amounts of hydrocarbons formed, as well as the infrared and energy-dispersive X-ray spectra of the solids, reveal that carbon and hydrogen of the ethylgermanes are contained in the volatile photolysis products, while germanium is the dominant element of the deposit. Ethylgermanes are much more prone to photolytic decomposition than germane, which makes them more suitable precursors for photolytic deposition of germanium. The form and morphology of the deposited layers have been investigated.

Laser-induced aerosol particle formation from a gaseous mixture of trimethyl(2-propynyloxy)silane and acrolein

Abstract Upon exposure to N2 laser light, a gaseous mixture of trimethyl(2-propynyloxy)silane (TMPSi) and acrolein (AC) produced sedimentary spherical aerosol particles with a mean diameter of ≈ 0.5 μm. The IR spectrum of the sedimentary aerosol particles showed bands characteristic of polyacrolein, and XPS showed two Si 2p bands assignable to elemental silicon and silicon bonded in an organosilicon polymer, indicating that TMPSi was incorporated into the parent aerosol particles of polyacrolein, and cleavage of Si-C and Si-O bonds took place in the aerosol particles. The nucleation process of the aerosol particles was investigated by measuring He-Ne laser light intensity scattered by the aerosol particles as formed under irradiation with N2 laser light.

Chemical vapour deposition of polycarbosilanes via ArF laser-induced photolysis of sila-, 1-methyl-1-sila- and 1,3-disila-cyclobutanes

Laser-induced photolysis of the title silacycles in the gas phase is dominated by cleavage of the four-membered ring and results in deposition of polycarbosilanes formed by polymerization of assumed transient silenes and silylenes. The polycarbosilane films are reactive towards oxygen.

CO2 laser-induced thermal chemical vapour deposition of polymers

Abstract Chemical reactions in the gas phase which are induced by CO 2 lasers and lead to the formation of organic or organometallic polymers are reviewed. The reactions involve the thermolysis of heterocycloalkanes, alkoxygermanes and acyclic organosilanes, the explosive decomposition of fluoromethylsilanes, and thermal chemistry in mixtures of silane with organic compounds. Attention is given to the mechanism of the gas-phase reactions as well as to the structure of the polymers.

Efficient laser-induced generation and polymerization of the highly unsaturated compound diethynylsilene in the gas phase

Abstract The CO 2 laser photosensitized (SF 6 ) decomposition of 1,1-diethynyl-1-silacyclobutane in the gas-phase involves a clean elimination of ethene to give a transient highly unsaturated diethynylsilene, which undergoes very efficient polymerization to yield saturated macromolecules with a cross-linked structure. The results reveal the very large enhancement of the ease of triple CC bond polymerization for molecules containing proximal CC and SiCH 2 bonds.

Laser-induced chemical vapour deposition of Si/C/H materials from monoorganylsilanes

Laser-induced photolysis of monoorganylsilanes RSiH3(R = H2CCH, HCC, ClHCCH and H2CCHCH2) produces thin Si/C/H films, thought to be saturated polycarbosilanes of low hydrogen content, and formed from unsaturated transients generated upon elimination of hydrogen and ethyne from the RSiH3 molecules. The films incorporate oxygen upon exposure to the atmosphere.