Time-Resolved Cavity Ringdown Measurements and Kinetic Modeling of the Pressure Dependences of the Recombination Reactions of SiH₂ with the Alkenes C₂H₄, C₃H₆, and t-C₄H₈

Abstract

Room-temperature rate constants for the pressure-dependent reactions SiH2 + ethene, propene, and t-butene have been determined at total pressures of 3.3 mbar < or = p < or = 300 mbar with Ar as buffer gas. SiH2 was detected by means of time-resolved cavity ringdown spectroscopy (CRDS), and the deconvolution of ringdown, kinetics, and laser bandwidth effect was accomplished with the extended simultaneous kinetics and ringdown model (eSKaR). In this way, pseudofirst-order rate constants could be extracted from nonexponential ringdown profiles. The recombination reactions, including the reaction SiH2 + i-butene, have been modeled based on the simplified statistical adiabatic channel model (SACM) and weak collision energy-grained master equation (ME) simulations. The influence of an interfering fast isomerization channel was investigated based on the Rice, Ramsperger, Kassel, Marcus theory (RRKM) and was found to be only important for the C2H4 reaction. Using ab initio energies (G3) and structures (MP2/6-311G(d,p)) as input parameters for the kinetic models, a consistent description of the pressure and temperature dependences of all four reactions was possible. In the temperature range 295 K < or = T < or = 600 K, the extrapolated limiting high-pressure rate constants, k(infinity)(C2H4)/(cm(3) x mol(-1) x s(-1)) = 1.9 x 10(14) (T/K)(-0.065), k(infinity)(C3H6)/(cm(3) x mol(-1) x s(-1)) = 1.3 x 10(14) (T/K)(0.075), k(infinity)(i-C4H8) = 1.8 x 10(14) cm(3) x mol(-1) x s(-1), and k(infinity)(t-C4H8)/(cm(3) x mol(-1) x s(-1)) = 4.6 x 10(13) (T/K)(0.21), are close to the collision number and are more or less temperature independent. In the case of ethene, probably due to the approximate treatment of rotational effects and/or the interfering isomerization process, the applied model slightly underestimates the falloff and thus yields too high extrapolated rate constants at p < 10 mbar.

Molecular Main Group Metal Hydrides

“…We would like to draw specific attention to the review by Hadlington, Driess, and Jones who document the use of modern molecular design principles and synthetic methods to access low-coordinate Group 14 hydride complexes, while discussing important pioneering work relating to the use of such species in catalysis . The parent inorganic silylene SiH 2 is often touted as a key intermediate formed during the decomposition of SiH 4 into thin films of Si. , As shown in Scheme , SiH 2 can be generated as a transient species by the flash photolysis of PhSiH 3 , while photolysis of Me 2 SiH 2 and 1-chloro-1-silacyclopent-3-ene ( 738 ) yield MeSiH and ClSiH, respectively. , The reactivity of SiH 2 with small molecules, such as O 2 , H 2 O, HCl, CO 2 , MeC­(O)­H, Me 2 O, alkenes, , alkynes, N 2 (the H 2 Si·N 2 adduct is stable at 10 K), NO, or silanes (e.g., MeSiH 3 ), can lead to E–H bond insertion, oxidative addition, hydride migration, or Lewis acid–base adduct formation, depending on the nature of the substrate (Scheme ). Furthermore, SiH 2 also has been the subject of numerous computational investigations. − Laser flash photolysis of germacyclopentenes at 193 nm (Scheme ) yields GeH 2 , either in the gas phase or solution, , and reactivity paths that mirror those exhibited by SiH 2 with small molecules have been observed. − In related work, gas phase laser flash photolysis of 1,3,4-trimethyl­germacyclopent-3-ene ( 739 ) yields transient MeGeH (Scheme ), while passage of an electric discharge through H 3 GeCl vapor affords the reactive halogermylene HGeCl .…”

“…977,978 As shown in Scheme 119, SiH 2 can be generated as a transient species by the flash photolysis of PhSiH 3 , while photolysis of Me 2 SiH 2 and 1-chloro-1- silacyclopent-3-ene (738) yield MeSiH and ClSiH, respectively. 979,980 The reactivity of SiH 2 with small molecules, such as O 2 , 981 H 2 O, 982 HCl, 983 CO 2 , 984 MeC(O)H, 985 Me 2 O, 986 alkenes, 987,988 alkynes, 989 N 2 (the H 2 Si•N 2 adduct is stable at 10 K), 990 NO, 991 or silanes (e.g., MeSiH 3 ), 992 can lead to E−H bond insertion, oxidative addition, hydride migration, or Lewis acid−base adduct formation, depending on the nature of the substrate (Scheme 120). Furthermore, SiH 2 also has been the subject of numerous computational investigations.…”

HCO formation in the thermal unimolecular decomposition of glyoxal: rotational and weak collision effects

“…This asymmetry is not accounted for by our simple J-averaging procedure and probably has to be compensated by using higher hDE down i values. 56 Full J-resolved 2D ME calculations should be capable to account for these effects, 35,57 but are still in their infancy and beyond the scope of this article. Fig.…”

Kinetics of the Thermal Decomposition of Ethylsilane: Shock-Tube and Modeling Study

“…Reaction 2b for example has no well-defined transition state, and we did not attempt to compute its rate constants. However, Friedrichs et al 50 directly measured the rate constant of the reverse reaction. Instead of the rate constant k 2b , the present mechanism provides the rate constant expression for the reaction C 2 H 4 + SiH 2 → cyclo-C 2 H 4 SiH 2 , determined by Friedrichs et al, 50 and in the mechanism, this reaction is also written as a reversible process.…”