The shock-induced thermal decompositions of vinylsilane and vinylsilane-d, (0.2% on argon) have been studied in the temperature range of 1085-1275 K, and at total pressures of about 3100 tom. In systems without silylene traps, some induced decomposition occurs which is attributed to the silylene chain sequence VSiH + C,H, + SiH,, SiH2 + VSiH, VSiH,SiH, + VSiH,SiH + Hz, VSiH,SiH + VSiH + SiH2. In the presence of silylene traps (butadiene and acetylene), the overall decomposition kinetics are log HVSiH,, s-'1 = 14.95 -63,268 ca1/2.303RT and log MVSiD,, s-l) = 15.14 -64,815 ca1/2.303RT. Three primary processes contribute to the decomposition: l,l-H, elimination, 1,2-H2 elimination, and ethylene elimination. Two mechanisms are proposed, one for exclusive primary process formation of C2H4, and the other for both primary and secondary formation routes. Modeling studies are reported which show that both mechanisms can be made compatible with the rate and product yield data within experimental errors.

The homogeneous gas-phase decomposition kinetics of methylsilane and methylsilane-d3 have been investigated by the comparative-rate-single-pulse shock-tube technique a t total pressures of 4700 torr in the 1125-1250 K temperature range. Three primary processes occur:CH:$iH3 -CH3SiH + HS (l), CH3SiH3 -CH4 + SiHz (2), and CH3SiH3 -CHa = SiH2 + H2 (3). The high-pressure rate constants for the primary processes in CH3SiH3 obtained by RRKM calculations are log ( k l + k s ) (s-l) = 15.2 -64,780 cal/@ and log kz (s-l) = 14.50

The rate constant for the reaction HO2+O3→OH+2O2 was investigated in a discharge–flow system at room temperature. HO2 was produced from the reaction sequence Cl+CH3OH→CH2OH+HCl and CH2OH+O2→HO2+CH2O. HO2 was detected by the OH(A–X) fluorescence produced from photodissociative excitation of HO2 at 147 nm. A computer modeling of the reaction kinetics occurring in the flow tube was carried out to confirm that contributions from secondary reactions were negligible at low HO2 concentrations. The rate constant was determined from first order decay of HO2 in excess O3. The measured reaction rate constant of HO2+O3 is (1.9±0.3)×10−15 cm3 molecule−1 s−1, which agrees well with published data.

The microwave spectra of C~NO and CDaNO have been observed and analyzed. The barriers to internal rotation are 1137±5 and 1095±7 cal/mole for CHaNO and CDaNO, respectively, a difference of 42 cal/mole which is thought to be real. The barriers were calculated by the internal-axis method with retention of higher terms in the usual Fourier expansion of the rotational energy and computation of the torsional integrals in the harmonic-oscillator approximation. The theoretical parameters were fitted to the data by a least-squares method and the uncertainties reported are standard deviations. Transitions having comparable Stark and quadrupole energies were used to calculate the dipole moment. Secular equations of second or third order were solved for each of the data points. The dipole moment components are I'a= 2.240±0.OO1 D, I'b=0.522±0.006 D, and I'total = 2.300±0.OO2 D. The quadrupole coupling constants of C~NO are 0.50± 0.16, -6.016±0.031, and 5.518±0.031 for the components along the a, b, and c axes, respectively. The corresponding values for CDaNO are 0.60±0.07, -6.007±0.020, and 5.41l±0.020. The N=O and C-N distances are not well determined by the data. The CNO angle is 112.6±1.0o.

The inelastic scattering of He 4 " by Ne has been studied as a function of angle 6 and energy loss AE over the range of barycentric energies E from 22 to 500 eV. Many levels of Ne are excited, including autoionizing ones, and excited He + is also seen. Excitation of the 2/> 5 3s configuration of Ne at about 16.8 eV could be resolved uniquely, and was studied in detail. The process does not occur in forward scattering, but only outside a threshold obeying the rule T C = (E8) c & 1035 eVdeg, typical of a curve-crossing interaction. It shows pronounced Stueckelberg interference oscillations, arising from the existence of two semiclassical trajectories inside the crossing point at r Qi with the property that the product of the wave number k and the angular spacing A0 between peaks is substantially constant, i.e.,Ab-2ir/kA0 = 0.44 a.u. These and other properties suffice to show that the upper state is attractive and to identify the transition with the outermost crossing that perturbs the elastic scattering of He + by Ne, which was earlier shown to be located at r c s 1.9 a.u. and at an energy of V c = 13.5 eV. The behavior of the reduced cross section p= 6 sm6(j(6 t E) at the first Stueckelberg peak shows that the transition probability peaks at an energy of about 25 eV, i.e., when the velocity at the crossing point is about 2.6 x 10 6 cm/sec. From this, the transition matrix element at the crossing is deduced by Landau-Zener theory to be roughly #i2^r

The kinetics and mechanism of the thermal decomposition of n-propylsilane have been studied by the single pulse shock tube-comparative rate technique a t pressures

A new theoretical r0 structure for vinyl fluoride has been derived using ab initio molecular orbital procedures. In addition, new experimental r0 and rs structures have been obtained through a reanalysis of existing experimental microwave data. Significant discrepancies are found between the new theoretical (125.4°) and experimental (127.6°) r0 estimates of the CCHu angle involving the hydrogen atom geminal to the substituted center. This is attributed to the relative insensitivity of the experimental structural fits to the precise value of this bond angle, an insensitivity that is associated with the proximity of the relevant atoms to inertial axes. Because of these difficulties, the best estimate of the experimental r0 structure for vinyl fluoride is obtained by taking the theoretical r0 value for the CCHu angle and determining the remaining parameters by a weighted-least-squares fit to the experimental data. Weighted-least-squares fits are found generally to provide more consistency in the derived structural parameters than unweighted procedures. It is found that fitting of isotopic differences in rotational constants (as opposed to the conventional fitting of rotational constants themselves) provides the structure for vinyl fluoride most similar to the theoretical r0 structure. Similar observations are found to hold for vinyl alcohol, for which new theoretical and experimental results are presented.

Ab initio theoretical studies on X2B10H10 (X = CH, SiH, N, P and Sb) have been done for all the three possible isomers. Unlike lower‐vertex heteroboranes, all the hetero derivatives have shown similar trends in the relative stabilities, the 1,12‐isomer being more stable followed by 1,7‐ and 1,2‐isomers, except for N and Sb. No conventional 1,2‐isomer for N could be found. Instead, a new nido isomer which is 18.1 kcal/mol higher in energy than the most stable isomer has been located. Any hetero group substitution to icosahedral R12H122− is found to be thermodynamically destabilizing. However, the Nucleus Independent Chemical Shift criterion shows that all compounds, except for 8, have similar aromaticity.