Neville L. Arthur

Arrhenius parameters for the reaction of H atoms with SiH4

The reaction H+SiH4 has been studied at 298–636 K in pulsed photolysis experiments with H atoms produced by the mercury-sensitised photolysis of H2 and detected by Lyman-α absorption. The rate constants obtained are given by Combination of our results with previously reported data gives for the temperature range 290–636 K.Simulation of the observed dependence of the measured pseudo-first-order rate constant on the H atom concentration at 298 K and 500 Torr yields k2=(4.3±1.0)×10-11 cm3 s-1 for the rate constant of the atom–radical reaction, H+SiH3.

Rate constants for H+(CH3)4−nGeHn, n=1–3

Abstract Rate constants for the reactions of H atoms with SiH 4 and the methylsilanes, (CH 3 ) 4− n SiH n , n =1–4, have been measured at 298 K in pulsed photolysis experiments with H atoms produced by the mercury-sensitised photolysis of H 2 and monitored by Lyman- α absorption. The values obtained, for n =1–4, respectively, are: k 1 =(2.70±0.20)×10 −13 , k 2 =(3.94±0.29)×10 −13 , k 3 =(3.88±0.21)×10 −13 , and k 4 =(3.38±0.16)×10 −13 cm 3 s −1 . These results show that methyl substitution enhances the reactivity of the Si–H bond towards H atom attack, and comparisons are made with the corresponding reactions of Cl, Br and O atoms.

Arrhenius parameters for the reactions of H atoms with PH3 and AsH3

Rate constants for H-atom attack on PH 3 and AsH 3 have been measured in flash photolysis experiments in which H atoms were generated by the Hg-sensitised photolysis of H 2 and monitored by Lyman-α absorption. The values obtained for PH 3 , in the temperature range 293472 K, are given by k 1 /cm3 s−1 = (1.09 ± 0.08) × 10−10 exp[(−1048 ± 27)/T]and for AsH 3 , in the temperature range 294–424 K, by k 2 /cm3 s−1 = (2.57 ± 1.30) × 10−10 exp[(−718 ± 160)/T]An evaluation of the available data on H + PH 3 has been carried out, and the best value for the rate constant over the temperature range 200–500 K is recommended to be k 1 /cm3 s−1 = (0.721 ± 0.041) × 10−10 exp[(−887 ± 19)/T]

KINETIC ISOTOPE EFFECT FOR THE REACTION OF H ATOMS WITH GEH4 AND GED4

Rate constants for H atom attack on GeH4 and GeD4 have been measured in pulsed photolysis experiments in which H atoms were produced by the mercury-sensitized photolysis of H2 and monitored by Lyman-α absorption. The values obtained for GeD4 in the temperature range 293–550 K may be represented by the expression Combination of the rate constants for GeH4 measured in this work with those previously determined in this laboratory gives, for the temperature range 293–455 K, The kinetic isotope effect indicated by these expressions is given by which yields . This is the first determination of the kinetic isotope effect for radical attack on a Ge(SINGLE BOND)H bond. The present results for the reaction of H atoms with GeH4 have been combined with previously reported data, and the best value for the rate constant over the temperature range 210–473 K is recommended to be

Arrhenius parameters for the reaction of H atoms with GeH4

Rate constants for H atom attack on GeH4 have been measured in pulsed photolysis experiments in the temperature range 293–473 K. H atoms were generated by the Hg-sensitized photolysis of H2 and were monitored by Lyman-α absorption. The values obtained are given by k8/cm3 s–1=(0.98 ± 0.13)× 10–10 exp[(– 926 ± 49)/T]. An evaluation of the available data on the reaction has been undertaken, and the best value for the rate constant over the temperature range 200–500 K is recommended to be k8/cm3 s–1=(1.21 ± 0.10)× 10–10 exp[(– 1008 ± 25)/T].

Reaction of H atoms with N2Oat 374[ndash ]628 K

The reaction of H atoms with N2O has been studied by flash photolysis in the temperature range 374–628 K at a pressure of 300 Torr, with argon as the bath gas. H atoms were generated by photolysis of NH3 and were monitored by Lyman-α absorption. At these temperatures the reaction is slow, and care was taken to establish conditions that ensured the measured rate constants were not affected by the occurrence of heterogeneous or secondary reactions. The values obtained are a factor of two less than those reported previously (Marshall etal., J. Chem. Phys., 1987, 86, 5540; J. Phys. Chem., 1989, 93, 1922) over this range of temperatures, and are given by Combination of our rate constants with earlier high temperature data (Albers etal., 15thInternationalSymposiumonCombustion, The Combustion Institute, Pittsburgh, PA, 1975, p. 765) confirms the curvature in the Arrhenius plot below 700 K observed previously. The combined data, for the temperature range 374–1110 K, can be represented by Simulation of the reaction shows that our results are consistent with the notion that the addition product HNNO is collisionally stabilized.

Rates of reactions of H atoms with some CVD precursors

Abstract Rate constants have been measured for the reactions of H atoms with SiH 4 , CH 3 SiH 3 , (CH 3 ) 2 SiH 2 , (CH 3 ) 3 SiH, GeH 4 , GeD 4 , CH 3 GeH 3 , (CH 3 ) 2 GeH 2 , (CH 3 ) 3 GeH, PH 3 and AsH 3 , over a range of temperatures, in pulsed photolysis experiments in which H atoms were generated by the Hg-sensitized photolysis (253.7 nm) of H 2 and monitored by Lyman-α (121.6 nm) absorption. Reactivity trends are identified and the relationship with the corresponding thermochemistry is discussed.

Arrhenius parameters for H+(CH3)4-nSiHn, n=1–3

Rate constants for the reactions of H atoms with the methylsilanes, (CH3)4-nSiHn, n=1–3, have been measured over the temperature range 298–580 K in flash photolysis experiments in which H atoms were produced by the mercury-sensitized photolysis of H2 and monitored by Lyman-α absorption. The values obtained, for n=1–3, respectively, are given by, The results show that methyl substitution increases the reactivity of the Si–H bond towards H atom attack. Comparison is made with previously published data, and with attack by other atoms and free radicals.

Arrhenius parameters for H+(CH3)3GeH and (CH3)2GeH2

Rate constants for the reactions of H atoms with the methylgermanes, (CH3)3GeH and (CH3)2GeH2, have been measured by flash photolysis in the temperature range 298–510 K. H atoms were generated by the mercury-sensitized photolysis of H2 and monitored by Lyman-α absorption. The values obtained are given by, respectively, The results indicate that the reactivity of the Ge–H bond towards H atom attack is increased by methyl substitution, the relative magnitude of the effect being the same as that observed for attack on the Si–H bond in the methylsilanes.

Mechanistic study of the Me2SiH–Me3Si radical system

Di- and trimethylsilyl radicals, generated by the reaction of H atoms with di- and trimethylsilane, react to produce three main products: 1,1,2,2-tetramethyldisilane, pentamethyldisilane and hexamethyldisilane. These products are formed by both radical combination and radical disproportionation reactions. The disproportionation reactions form Me2Si which inserts into the Si–H bonds of the reactants. From a quantitative determination of the disilane products as a function of the reactant ratio, a value for the branching ratio of cross-disproportionation of di- and trimethylsilyl radicals relative to the branching ratio for the disproportionation of dimethylsilyl radicals can be extracted. Our results provide strong evidence that the ratio of the rate constants for hydrogen abstraction from di- and trimethylsilane by H atoms is larger than absolute rate measurements suggest. Analysis also shows that the geometric mean rule for cross-radical reaction is closely obeyed. Disproportionation reactions yielding silaethenes occur to a minor extent and are responsible for the formation of six trisilanes. Secondary reactions, mainly initiated by H-atom abstraction from tetra- and pentamethyldisilane by silyl radicals, also take place. The relative rate constants estimated for these reactions are in agreement with a previous determination.