Energy transfer in thermal methyl isocyanide isomerization. Dependence of relative efficiency of helium on temperature

Assessment of Free Radical Catalysis in Thermal Methyl Isocyanide Isomerization. Variation of Inert Gas Efficiency with k/k∞

“…Propylene and propane fall on the same fall-off curve, within experimental error. The collisional activation efficiencies of these gases at infinite dilution in the second order, low pressure region, po(m), have been determined previously (5) at 280 "C to be virtually identical (0.61), which accords with their close superposition in the figure; at 230 "C, the efficiency value would be increased a little to -0.63 (6).…”

“…7 (I) of ref. 6, it is seen that the value h ( m ) = 0.63 corresponds to a reduced parameter E ' = 2.0, where E ' is defined as E' = (AE)/ ( E +); (AE) is the average amount of energy lost per collision and (E + ) is the average excess energy above threshold in the low pressure regime. (E') has been calculated (8) for methyl isocyanide and is 425 cm-', whence (AE) is found to be 850cm-' for propylene and propane.…”

Energy transfer in unimolecular reactions at high temperatures

“…These results are entirely in agreement with those obtained from chemical activation experiments [ 131. For the methyl isocyanide-helium system, the variation of P with dilution has also been studied [14], and the prcdicted [lS] decrease was observed. Increasing temperature also lowered /3 from 0.29 a t 210°C to 0.21 a t 320°C [15]; this is also predicted by the theory [la, 161. The theory of collisional energy transfer has also been examined in detail by Troc [17], using a versatile thrce-parameter model of energy transfer. From this work he was able to estimate (AE).…”

Fall-off behavior of a thermal unimolecular system in the presence of a weak collider inert bath gas

“…The value reported earlier8 was /3o(°°) = 0.25, after conversion to 245°from 280.5°b y the appropriate factor. 4 The main contribution to the discrepancy, such as it is, comes from the different values of the substrate activation rate constants kaA used in evaluating dp. If the low-pressure values of Chan, et al,8 are used here, instead of the transposed SR curve, the present work with helium gives do(°°) = 0.23, which is in excellent agreement with the earlier result.…”

“…3 The dependence of efficiency on temperature has also been investigated with helium bath gas. 4 No systematic study has ever been made of the variation of the collisional efficiency with the order of reaction, Le., with the degree of fall-off. That is to say, no comprehensive example exists of unimolecular fall-off in the presence of an inert gas.…”