Recent works on compounds of persilyl-substituted π-electron systems are summarized and reviewed. π-Electron systems include. acetyl, ene, ethylene, allene, butatriene, trimethylenemethane, methylenecyclopropene, cyGlobutadiene, fulvene, benzene, and benzene valence isomers. Some transition-metal complexes of these compounds are included as well.
Since silyl groups perturb π-electron systenis strongly by both steric and electronic effect, these compounds exhibit qui, te unusual and interesting physical and chemical properties. For example, tetrakis(trimethylsilyl)ethylene and hexakis(trimethylsilyl)benzene show reversible thermochromism. The latter undergoes facile valence isomerism to the corresponding Dewar benzene and prismane. Facile transition-metal complex-induced 1, 2-silyl shift is also notable for bissily-substituted acetylene systems. As a result, novel transition-metal complexes of fulvene, trimethylenemethane, and methylenecyclopropene were obtained. The latter has been unprecedented so far. X-Ray crystallographic analyses of these compounds revealed interesting features on the structures.

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Synthesis of optically active silaorphenadrine, silicon analogue of orphenadrine [N, N-dimethyl2-[phenyl(o-tolyl)methoxy]ethanamine] was investigated. (Methylphenyl-o-tolylsilyl)methanamine, which wa s obtained by four steps reactions starting from dichlorodimethylsilane, was resolved by using 2-phenylpropionic acid as a resolving agent. The conversion of optically active (methylphenyl-o-tolylsilyl)methanamine to optically active methylphenyl-o-tolylsilane, a precursor for the synthesis of optically active sila456orphenadrine, was carried out successfully. Each of (+)-and (-)-isomer of silaorphenadrine was obtained by treating. (-)- and (+)-methylphenyl-o-tolylsilane with 2-(dimethylamino)ethanol in the presence of palladium/carbon, respectively. Configurations of silaorphenadrine and the intermediates were determined by the derivatization of methylphenyl-o-tolylsilane to methyl (1-naphthyl)phenylsilane system, of which configuration was already established.

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Although alkali metal salts of hexamethyldisilazane (HMDS) are well-known to be hindered bases for organic synthesis, only a few reports concerning synthetic utilities of disilazane itself can be found in the literature. In this paper, we examined the reactions of acid anhydrides (( 1), (6), (12)-(14)) and an acid chloride (5) with HMDS and N-phenylhexamethyldisilazane (PhHMDS). While the reaction of phthalic anhydride (1) with HMDS in refluxed CH2Cl2 gave phthalamic acid ( 3), the similar reaction in acetonitrile or chlorobenzene gave phthalimide (2). With PhHMDS, (1) was converted into N-phenylphthalimide-( 4) in chlorobenzene. Phthaloyl dichloride (5) reacted with HMDS o(r PhHMDS to give 2) or (4), respectively. From the mechanistic study, (2) was postulated to be obtain (ed from trimethylsilyl o-(N-trimethylsilylcarbamoyl)benzoate, which was converted into (3) by hydrolytic desilylation, via an intramolecular elimination of hexamethyldisiloxane. Maleic anhydride (6 ) was transformed into maleamic acid (8), (9), together with only a trace amount of maleimide (10), under the employed conditions. As for the cyclization, an intermediate obtained from (5) was less reactive than the one obtained from (1). The reaction of benzoic anhydride (12)-(14) with HMDS gave benzamides (15), (17), (19) or dibenzamides (16), (18), depending upon the quantity of HMDS and the substituent. Dibenzamide was found to be obtained not via an intermolecular elimination of disiloxane but via a nucleophilic attack of N-silylbenzamide toward benzoic anhydride.

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The reaction of cyclododeey1 acetates derived from secondary alcohol, cyclododecanol, with 4 equivalents of diphenylsilane in the presence of 0.5 equivalent of di-t-butyl peroxide (DTBP) as a radical initiator gave cyclododecane. The reaction did not proceed without DTBP. The best results were obtained in the case of acetate as ester compared w ith the other esters such as isobutyrate, pivarate, or benzoate. Acetates derived from primary and tertiary alcohols were also deoxygenated, although the yields were relatively low. In the case of the deoxygenation of acetylated sugars, the yields were poor and a large amount of by-products were produced. It seems that the major factor is related to the fact that diphenylsilane has two reaction site and readily disproportionate to the other silanes.

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An N-silyl-1-azaallyl anion [3 a], generated from an α-silyl carbanion [1a] of 3-methy1-5(trimethylsilylmethypisoxazole and benzonitrile [2 a], reacted with an excess amount of perfluoro(2-methyl-2-pentene) [5 ] in the presence of various kinds tertiary amines i n tetrahydrofuran to give 4-fluoro-5-(3-methy1-5-isoxazoly1)-2-pentafluoroethyl-6-phenyl-3(trifluoromethyppyridine [6 a]. Under the reaction conditions determined as optimum, the corresponding five pyridines [6 a]-[6 e] were prepared from the anion [1 a] and p-substituted benzonitriles [2 a] -[2 e] [Ar=C₆H₅, p-CH₃, C₆, H₄, p-CH₃OC₆H₄, p-C1C₆H₄, p-(CH₃)2NC₆H₄]in good yields (67, 48, 70, 51 and 56%, respectively). The reaction was extremely accelerated by the trimethylsilyl group of the anions [3]. However, an analogous reaction of the anion [1 b], derived from 2-(trimethylsilylmethyl)pyridine, did not give the 4-fluoropyridine derivative [6 f], but gave the corresponding 4-pyridone [8 f] in poor yield (22%).

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Composite precursor powders with cordierite-mullite composition were prepared by copolymerization of metal alkoxides. Cordierite (2 MgO.2 Al₂O₃.5 SiO₂) precursor solution was prepared by copolymerization between partially hydrolyzed tetraethyl silicate (TEOS) and Mg-Al double alkoxide. On the other hand, alminium iso-propoxide was refluxed in isobutyl alcohol followed by copolymerization with partially hydrolyzed TEOS so as to prepare homogeneous mullite (3Al₂O₃.2SiO₂) precursor solution. By mixing cordierite and mullite precursor solutions, composite precursor solutions were obtained. Excess amount of water was added to the composite precursor solutions to precipitate homogeneous composite precursor powders. The precursor powders were heat-treated up to 1400°C. Mullite phase was identified at temperature as low as 900°C. α-cordierite phase was formed at 1200°C through a reaction between sapphirine (4 MgO.5 Al₂O₃. 2SiO₂) and amorphous silica. The calcined composite precursor compacts could be sintered into dense bodies by 1300°C firing. From the results, the chemical processing of the composite precursor was considered to be effective to prepare homogeneous cordierite-mullite composite at low temperature.

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Poly[(3-sulfopropyl)siloxane]s [4] were synthesized by sulfonating in aqueous solution of Na₂S0₃ the corresponding poly[(3-bromopropyl)siloxan14]s [3], which were obtained b y copolymerizing (C₂H₅0)₃Si(CH₂)₃Br [1 ] and (C₂H₅SO)₄Si [2] with molar ratio, n(=[1]/[1]+[2]), of 0.1-0.5. Among the polysiloxanes [4 ], those with n=0.2 and 0.3 were solids with acidity of 1.0 and 1.3 mmol. g-1, respectively. The catalytic activities of the two polysiloxanes [4] for an acid-catalyzed reaction and their thermal stabilities were examined.
In the vapor-phase conversion of ethanol, dehydration reaction proceeded to yie ld mainly diethyl ether at 453 K; the ethanol conversion was 87% (n=0.2) or 70% (n=0.3), and the activities were stable for 1-4 h of on-stream time. Thermal treatment of the polysiloxanes 4] at 543 K for 12 h under a nitrogen stream had little effect on the catalytic [acitivity for the dehydration of C2H5OH; the thermal stability of [4] is higher than an anion-exchange resin, Amberlyst-15. The p olysiloxanes [4] showed a catalytic activity also for the liquid-phase esterification of acetic acid with isobutyl alcohol. During the esterification, catalytically active components of [4] were little eliminated from the polysiloxane linkage.

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Hydrolysis of 3', 5'-0-(di-t-butylsilanediyl)deoxyribonucleosides and ribonucleosides was investigated in the presence of tetrabutylammonium fluoride in THF. The ribonucleoside derivatives were more smoothly converted to the parent nucleosides than the corresponding deoxyribonucleoside derivatives regardless of the kind of the base. A close ex amination of the desilylation reaction of the thymidine derivative revealed that the desilylation proceeded in two stages and partially hydrolyzed compounds, 5'- and 3'-O-(di-t-butylhydroxysilyl)thymidine, were found as by-products in the second stage. The masking of the 3'-hydroxyl function of 5'-O-(di-t-butylhydroxysilyl)thymidine by an acetyl group markedly facilitated the cleavage of the silyl group. This indicates that a hydrogen bonding between a fluoride anion and the 3'-hydroxyl group interferes with the fluoride attack at the 5'-silyl po sition. In the case of the ribonucleoside derivatives, 2'-O-hydroxysilyl derivatives were also found as well as 5'- and 3'-O-hydroxysilyl derivatives. The occurrence of the 2'-silyl compound suggests the existence of a 2', 3'-cyclic silyl intermediate which contains reactive 1, 3, 2dioxasilacyclopentane structure. The mechanism of desilylation via the 2', 3'-cyclic silanediyl intermediate has been proposed for the ribonucleoside derivatives.

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Methylsilazanes prepared by the methods reported previously have multifunctional amino groups in a molecule, and show self-condensing character, and were possible to give several forms. Methylsilazane oligomers undergo polymerization and change their states gradually from oily liquid to gelous solid and finally transform into insoluble and infusible solid. Methylsilazane oligomers are easily polymerizable, and therefore it is very difficult to find optimum conditions for preparation of specific forms. In order to resolve these problems, thermal conversions of methylsilazane oligomers were, r investigated. From the resulting diagrams, the thermally converted methylpolysilazanes were divided into three stages according to their heat treatment temperature. In the first stage, heat-treatment temperature was lower and therefore thermally converted methylsilazanes showed only increasing their viscosity, but yet fluid. In the second stage, the converted methylpolysilazanes became gelous solid at room temperature, and showed various softening temperatures. Thermoplasticity of them were controllable by heat treatment. In the third stage, the converted methylpolysilazanes became rigid mass, and they are no longer soluble and fusible. Among three stages, the most applicable one seems to be the second, in wnicn tnermaily converted methylsilazanes, so-called thermoplastic methylpolysilazanes are involved, which have characters defined by the softening temperature. Such a defined thermoplastic methylpolysilazane as a precusor can be useful following preparation of ceramic fibers and films as well as binders. PassibilityasPrecursorstoCeramic.IV.

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Microcrystalline hydrogenated silicon (μc-Si: H) which consists of very small silicon microcrystals surrounded by hydrogen atoms can be fabricated by RF sputtering in pure hydrogen onto a low temperature (about 100 K) substrate. We propose the growth model for such Si: H material, in which the inicrocrystals have been partially formed in the gas phase by the reaction of SiH₃ radicals, and then rearranged and reacted each other on the substrate by the light irradiation effect from the hydrogen plasma. This model can well explain our experimental results as well as the estimation from other fabrication methods such as plasma chemical vapor deposition.

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Despite of homologous elements, the bond nature and reactivity of silicon compound are different from those of carbon compound. In order to clarify the difference, theoretical studies of silane as a prototype of silicon compound were reviewed. Silane is a key compound for CVD. It has been believed that the important process of CVD is a silane decomposition reaction to form silylene (1) SiH₄ → SiH₂+H₂, followed by silylene insertion to σ bond (2) SiH₂+R-X→R-SiH₂X. There are some theoretical results for reaction (1) and (2 ), respectively. However, there has never been considered the reaction of ( 3 ) SiH₄+R-X→R-SiH₂X+H₂, as a two-step reaction composed of reaction (1 ) and ( 2 ). Therefore, our recent studies of the one-step reaction of ( 3 ) (R-X=SiH₄ NH₃ H₂O and SiH₃OH) without silylene formation were compared with those of the two-step reaction of ( 3 ). As a result, for R-X=NH₃, H₂O and SiH₃OH, the one-step reaction has an advantage over the two-step reaction under kinetic control. This may predict that there exists some milder synthetic condition of silicon compound than that of silylene formation. The specific bond nature and reactivity of silicon compound was examined by using the Bader-Pearson's perturbation theory.

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We have previously reported that the silicon-carbon bonds in silafunctional compounds are cleaved by hydrogen peroxide in the presence of a fluoride ion to form the corresponding alcohols. We have proposed a plausible mechanism which involves penta-coordinate silicon species as intermediates and hexa-coordinate silicon species in the transition state. Thus, tetra-coordinate silicon compounds are converted into penta-coordinate silicon species via the interaction with a fluoride ion, which are attacked by hydrogen peroxide as the sixth ligand in the rate-determining step: In the hexa-coordinate species, the organic group may migrate with a carbanionic character from silicon to the adjacent oxygen of the hydroperoxy ligand. The supporting evidence includes [1] activation by a fluoride ion and high reactivity of penta-coordinate diorganotrifluorosilicates, [2] rate-dependence on the concentration of hydrogen peroxide, [ 3] retention of configuration of the carbon center, (4) acceleration by an electron-withdrawing substituent on the organic group, [5] dual steric effects, steric acceleration and steric hindrance effects. Based on the last steric effects and X-ray structures of pertinent penta-coordinate silicon compounds, attempts have been made to analyze the lines of attack by hydrogen peroxide on penta-coordinate silicon species.

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Photochemical and photophysical processes of organosilicon compounds have been studied. Dual (local and CT) emission has been found in aromatic disilanes. The intramolecular CT fluorescence has a broad and structureless band with a large Stokes shift. The CT emission originates from the 1(2 pπ, 3 dπ) state having an in-plane long-axis polarization, which is produced by the 2 pπ* (aromatic ring) → vacant 3 deπ (Si-Si bond) intramolecular charge transfer. The CT state plays an important role in the photochemical and photophysical properties of phenyldisilanes. The intramolecular CT occurs very rapidly (< 10 ps) both in nonpolar media at 293 K and in a polar rigid matrix at 77 K. At room temperature a longlived 425 nm transient (silene) is produced with a time constant of 30 ps from the CT state. The photolysis of cyclotetrasilanes is remarkably dependent on their molecular structures: two molecules of the corresponding disilene are produced from the Si state of planar cyclotetrasilanes, while silylene is generated by ring contraction in the S, state of bent cyclotetrasilanes. Remarkably large Stokes shifts are observed in these cyclotetrasilanes. Dimethylsilylene with a transient peak at 470 nm is observed by laser photolysis of cyclohexasilane. The dynamic behaviors of the intermediates have been studied by nanosecond laser photolysis. The phenylsilyl radical is generated by photolysis of phenylsilanes in rigid glass at 77 K, which gives a structured emission similar to that of benzyl radical.

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The correlation between the plasma reactivity and the electronic state at excited states of vinylsilane is examined. A quantum chemical analysis is based on the two-center bond energy and the localized orbital energy obtained by using MNDO molecular orbital method. As shown in Table 1, the two-center bond energy of the C=C bond at the lowest excited state is more positive than that of the ground state. The π bond character disappears at the lowest excited triplet state (T₁) as shown in Table 2. Thus, the vinyl π bond is expected, to be activated at the lowest excited state. On the other hand, the Si-C bond is calculated to be weak at the second lowest excited state as shown in Tables 1 and 2. This tendency is more pronounced at the triplet state than at the singlet state. The excitation energy to the T, state is much lower than that to the other excited states (Fig.1). Thus, the reaction via T₁ state is expected to be predominant when the excitation energy is low. The experimenta l results of the rf plasma reaction of vinylsilane is consistent with this prediction. XPS and IR spectra of the film produced by the plasma reaction of vinylsilane (Fig.4 and 5) sh ow that a carbon-carbon skeletal network is formed via the cleavage of the vinyl π bond when the supplied power is low. The excitation with a higher power facilitates the cleavage of Si-C bond. Thus, the C/Si ratio of the film produced can be controlled by the supplied power. The quantum chemical calculation can be a powerful tool for designing the reaction mode of such a complex reaction as the plasma chemical decomposition of vinylsilane.

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Photoreactions of octaphenylcyclotetrasilane and azobenzenes give 1-(1, 2-diarylhydrazo)1, 2, 2, 3, 3, 4, 4-heptaphenyl-1, 2, 3, 4-tetrasila-1, 2, 3, 4-tetrahydronaphthalenes (1) and (2) in good yields which were identified by NMR spectra and/or X-ray crystal analysis. In the reaction of azobenzene with octaphenylcyclotetragermane, 1, 2, 3, 3, 4, 4, 5, 5, 6, 6decaphenyl-1, 2-diaza-3, 4, 5, 6-tetragermacyclohexane (3) is obtained.

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The hydrosilylation by using metal-complex catalysts is the most useful reaction and especially platinum-catalyzed hydrosilylation is widely applied to commercial silicones, such as room-temperature vulcanization rubber (RTV) and release paper. From a practical point of view, however, retarders ha+e been used to control hydrosilylation effectively.
In this article, we made a study of the retarder of platinum-catalyzed hyd rosilylation reaction for the estimation of the retarder's capability. Differential scanning calorimetry (DSC) method was used in this study. In particular, acetylene derivatives were selected as the retarder, and exothermic curve of hydrosilylation was measured by DSC method.
As a result, DSC method was useful for evaluation of retarder's effectivenes s. Both the initial temperature of hydrosilylation and the shape of theexthermic curve depended up o n the structure of acetylene derivative (Fig.1). The hydrosilylation was controlled effectively by acetylene alcohols and their silylated derivatives, but not by alkynes with no functional group. The acetylene alcohols containing a bulky substituent on the a-carbon was the most effective.
The content of triple bond in the acetylene derivative was defined acetylene value (molfg). The peak temperature of the exothermic curve was related to the acetylene value. It was found that the effective retarder had the structure of C-C multiple b ond and oxygen atom or nitrogen atom on the carbon atom next to C-C multiple bond. The distance between the multiple bond and the functional group on the effective retarder was estimated to be 2.0Å.

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α-Silyl ester has been known to be specific silicon compound because of the easiness of the Si-C bond cleavage under mild conditions. In this investigation, various silyl esters were prepared and allowed to react with methanol.
Consequently, the following substituent effects of R¹, R² in R¹Me₂SiCH₂CO₂R² on the reactivity with methanol have been revealed:
(1) the Si-C bond cleavage are accelerated by electronwithdrawing substituents,
(2) methanolysis is inhibited by bulky substituents presumably due to the stereochemical effect,
(3) reactivity: R¹Me₂SiCH₂CO₂R²
R¹: H >C1CH ₂ > Ph >CH₂=CH > Me > n-Pr>n-C₃H₁₇ >i-Pr
R²: Ph>Me>Et>n-C₈H₁₇

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SiO₂-supported Cu catalysts were prepared by alkoxide method employing copper(II)nitrate, ethylene glycol and ethyl silicate, followed by calcination in a static atmosphere and reduction in a flow of hydrogen, and then applied to dehydrogenation of methanol leading to methyl formate. During the preparation of catalysts, it was found that the organic compounds containing Cu decompose on heating near 250°C, and the compounds related to Si decompose at about 320°C. Prior to the reaction, CuO and Cu₂O were completely reduced to Cu metal in and/or on SiO₂. These Cu/SiO₂ catalysts prepared by alkoxide method showed higher activities for the reaction than those prepared by ion exchange method.

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The behavior of radicals produced in polycarbosilane fiber by γ-ray and electron irradiations was investigated by ESR measurement. The produced radicals were Si and C radicals. At room temperature, most of the radicals reacted with each other, and polycarbosilane molecules were crosslinked under vacuum. Some of radicals, which didn't contribute to the crosslinking, were fairly stable under vacuum, but were well oxidized by the exposure in air. A lot of oxygen was introduced into polycarbosilane fiber with oxidation of the radicals. The radicals decreased by the heat treatment under vacuum. The radical concentration of polycarbosilane fiber heat-treated at 513 K for 10 min under vacuum was below 1% for that before the heat treatment.

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Electronic structures of polysilanes are calculated theoretically and are discussed in the light of such experimental data as UV absorption, photoluminescence, carrier mobility and so on. Conduction and valence bands are formed by the sigma conjugation along a silicon backbone chain. The band structures corresponds to those of direct allowed type semiconductors. Substitution by larger alkyl side chains decreases the band gap slightly. With aryl-side-chain substitution, skeleton-pendant group interaction by sigma-pai mixing results in a decrease in ionization potential and the appearance of efficient visible luminescene. Trans-type polysilanes are more stable and have narrower band gap energies and smaller effective masses compared with gauche-type polysilanes. The existence of a gauche link in a trans-conformation has little disturbance for the sigma conjugation along a backbone chain. Band structures of polysilanes with multiphases correspond to the one dimensional heterojunction structure. Electrons and holes localize in the smaller gap region by the potential barrier. The barrier height for electrons is much larger than that of holes, which is the origin of the large mobility difference between them. Silicon-based polymers form a dimensional hierarchy from oligosilane to crystal silicon, and through polysilanes, ladder polymers, plane polymers, polysilane alloys, clusters, and amorphous silicons. The increase in the network dimensions is accompanied by the increase in sigma conjugated area and result in the reduction of energy gap values. This idea was confirmed by the photo-luminescence spectrum measuremens for four kinds of silicon based polymers with different network dimensions between one and three.

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Fifty organo silicon compounds were screened as to their antitumor effect by using several animal transplantable tumors such as Ehrlich carcinoma (EHC), Sarcoma-180 (S-180), Lewis lung carcinoma (LLC), B-16 melanoma (B-16 M), L-1210 and P-388 leukemia. Among these compounds, 2-(2-trimethylsilylethyl)thioethylamine (SDK-12 A) was found to be effective by oral administration on solid tumors of EHC, S-180, LLC and B-16 M, but SDK-12 A was found to be ineffective on L-1210 and P-388 leukemia.
The effect on EHC, S-180 and B-16 M was superior to that of 5-FU administered intraperitoneally and the effect on LLC was equivalent to that of 5-FU. SDK-12 A was found to be low toxic and after the oral administration of 1/5 LD50/day to mice for 10 days, any toxic symptoms were not observed.
This compound showed an inhibitory effect on the metastasis of both of B-16 M and LLC. Furthermore, SDK-12 A showed activation of the delayed type hypersensitivity response of mice bearing B-16 M. From these findings, it may be suggested that SDK-12 A is a unique drug possessing a dual effect for inhibition of the tumor growth and activation of the delayed type cellular immunity.

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Dual-layered photoreceptors using τ-form metal-tree phthaiocyanine for charge generation material and poly(methylphenylsilylene) (PMPS) for charge-transport material were studied with the electrophotographic properties. We compared them with well-known poly(Nvinylcarbazole)(PVK) about sensitivities, surface voltages, residual voltages and fatigues for ultraviolet light. Both PMPS and PVK have been able to form the thin films for their own adhesiveness.
The photoreceptor using PMPS had high sensitivity (more than 0.5 μJ/cm²) for the light sources in the region of 600-800 nm. In addition, PMPS surpassed than PVK for surface voltages and residual voltages, however, the amount of dark decay was larger than PVK. Some effective values could be drawn on the basis of above data, especially capacitance, specific dielectric constant, time constant of dark decay and dark resistance. Their values were reasonable on the results of electrophotographic measurements, and we calculated the specific dielectric constant of 3.35 for PMPS and 3.87 for PVK, respectively.
The fatigues for ultraviolet light were studied by means of the comparison of electrophotographic values and irradiational time and intensity of light, and we measured the molecular weight distribution by GPC. As a result of these measurements, we found that PMPS were cleaved in lower molecular weight products and were polymerized simultaneously. It can therefore be presumed that the increase of surface voltage and residual voltage with PMPS because the cleavage and polymerization of PMPS by ultraviolet light.

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A series of Y-Si-A1-O-N glasses, of which cation composition was same, were prepared b y melting Y₂O₃, Al₂O₃, SiO₂, Si₃N₄ or A1N at high temperature. Densities of the oxynitride glasses increased with nitrogen content up to 7 at% and leveled off. On the other hand, mechanical properties, such as hardness, Young's moduli and fracture toughness, of the glasses increased with nitrogen content in the glasses. The results of a FT-IR measurement suggested_that the microstructures of the oxynitride glasses changed with nitrog en content in the glasses. In the case of the same nitrogen and silicon content, mechanical properties changed with Y/A1 ratio in the glasses.

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A time resolved optoacoustic technique was used to measure the vibrational relaxation times of SiH_nF_4-n, (n=4, 3, 2, and 0) diluted in Ar. Fundamental vibration-rotation bands of these molecules were excited by using a line tunable CO₂ laser. It was found that several vibration-rotation lines of SiH₄(v₄), SiH₃F(v₄), SiH₂F₂(v₂) and SiF₄(v₃) coincided with the CO₂ laser lines, as shown in Fig.1. The vibrational relaxation times obtained in the prese nt work are summarized in Table 1 together with the existing experimental data on CH₄, and its fluorine substituents. It is noted that the self-relaxation rate of SiH₂F₂ is slower than that of CH₂F₂ in spite of its lower frequency of the lowest vibrational normal mode. This observation is in conflict with the prediction of simple adiabatic theories for V-T energy transfer. A theory for V-R, T energy transfer proposed by Nikitin and Moore was applied to explain this anomaly. Predictions of this V-R, T theory were found to be consistent with experimentally observed variation of the relaxation rates along with the number of hydrogen atoms, n, in SiH_nF_4-n, and CH_nF_4-n, . Slower vibrational relaxation of SiH₂F₂ than that of CH₂F₂ is caused by its larger effective reduced mass which is defined by equation ( 4 ). Not only the amount of energy transfered but also the effective reduced mass have large effect on the vibrational relaxation rates of these molecules.

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The electronic structure of poly(dimethylsiloxane) was studied by UV photoelectron spectroscopy. The results using rare gas resonance lines (Fig.1) give an accurate ionization energy of 8.3 eV, while the spectrum by synchrotron radiation (Fig.2( a )) gives the whole valence electronic structure. From the comparison with the data of related compounds in Fig.2 and with the density of states of unsubstituted polysiloxane calculated by Takeda an d Shiraishi (Ref.7) (Fig.3), the features in Fig.2 a are assigned as follows: A is derived from 0 2p lone pairs, B from the Si-C bonds, C from the C-H bonds, D from the Si 3s leves, E from the C 2s levels, and F from the O2s levels. The comparison of the present results with those of poly(dimethylsilylene) shows that the σ conjugation in poly(dimethylsilylene), which leads to the low ionization threshold energy and high conductivity upon doping, is effectively broken in poly(dimethylsiloxane), resulting in good insulating property. The localized nature of the electronic states in the Si-O systems leads to the increase of the ionization threshold from poly(dimethylsiloxane) to SiO₂ by the removal of electron-donating methyl groups (Fig.4), in contrast to the decrease in the catenated silicon systems from poly(dimethylsilylene) to silicon due to more effective delocalization in the three-dimensional system than in the one-dimensional system.

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