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Publkatwn costs assisted bu the National Science FoundationKinetic data for the homogeneous exchange of equimolar mixtures of hydrogen chloride and deuterium in the presence of an inert gas diluent were obtained by the analysis of infrared emission profiles of HC1 and DC1 and time-resolved mass spectra of m/e 36 and 37. The reaction was studied behind reflected shock waves over a temperature range of 1700-2800°K, a total density variation of 1.7-4.0 X 10-6 mol/cm3, and observation times of 500-750 Msec. Equilibrium amounts of HC1 and DC1 were observed in several of the experiments performed a t higher temperatures. Both argon and neon were used separately as diluents. The results from the infrared emission shock tube and the time-of-flight mass spectrometer shock tube were in agreement within one standard deviation of the Arrhenius plots. The rate of product formation was found to be nonlinear with respect to time. The formation of the mole fraction of DC1 (~D C I = [DCl]t/[HCl]o) using both sources of data is represented by the equation (1 -~D C I [~ + (~E C I /~D C I )~~] ) = exp(-k[M]t2), where k = 1016J2~o.80 exp (-34,340 i . 3130/RT), cms mol-l.sec-3. When the rate is expressed on a concentration basis, the combined order dependence of the reactants was shown to be consistent with a value of one. The difficulties in explaining the rate lam in terms of an atomic or molecular mechanism are discussed.

A complementary shock tube facility was used to study the reaction of equimolar mixtures of HBr and D2 diluted by inert gases over the temperature range 2030-2515 K. The total gas density in the reflected shock zone was varied, 1.68-1.92 X 10~6 mol/cm3. One set of experiments involved the analysis of infrared emission from HBr and DBr. The second set of data was collected using a time-of-flight mass spectrometer to sample the reacting gas mixture at 20-µßß intervals. Both sets exhibited a quadratic time dependence with respect to product formation. The combined order with respect to the reactants was found to be second order. Due to experimental difficulties, attempts to determine the order with respect to inert gas dependence were not successful. The kinetic profiles were fit to the equation [1 -%/dbJ = exp(-[HBrjo, t2),k -IQ22.31 ±0.48 exp(-83,020 ± 4970/RT) cm3 mol"1 sec"2. Assuming an order of one for the inert gas dependence, reaction profiles for an atomic mechanism were calculated using the experimental data presented herein and a collection of literature rate constants for the dissociation and three-center steps. Good agreement was obtained. This is the first report of a shock tube study involving the exchange of a diatomic molecule with deuterium that may be explained in terms of an atomic mechanism.

A shock tube coupled to a time-of-flight mass spectrometer was used to study the exchange reaction, CD4 + HC1 CDsH + DC1, over a density range 1.7-4.1 X 10"6 mol cm"3 in the temperature region 1600-2500°K. In the lower temperature range (1600-1900°K) DC1 exhibits a quadratic time-dependent growth rate while at higher temperatures (2200-2500°K) increase of DC1 is a linear function of time. The only chlorine-containing product is deuterium chloride. Rate constants extracted from the quadratic and linear regions yielded activation energies of 51 and 30 kcal mol"1, respectively. An atomic mechanism for the exchange predicts both time dependencies and the transition between them. Pyrolysis of methane occurred along with the exchange but the growth rate of the products ethane, acetylene, and diacetylene was shown not to be catalyzed by the presence of HC1. Acetylene was the major product of the pyrolysis. Exchange was observed in both major and. minor products. The ratio CHACEE was less than one when pyrolysis products were not detected and greater than one when they were present. This finding suggests the presence of methyl radical in the reaction mixture. The results are discussed in terms of an atomic mechanism.Professor Bauer and his coworkers studied the CH4 + D2 reaction in the temperature range 1440-1755°K (SPST) under conditions of negligible 02 impurities.6 Samples extracted from the reflected zone were analyzed with a mass spectrometer for CH4, D2, CHgD, and HD. Evidence for methane pyrolysis was not found. The reaction is reported to proceed through a four-center complex in accordance with the vibrational excitation mechanism proposed by Bauer.3a Burcat and Lifshitz (BL)6 studied the exchange system CH4 + CD4 in the temperature region 1340-1745°K (SPST). They report a zero-order dependence with respect to inert gas although Bauer found an order of 0.6 for the inert diluent. BL interpreted their results in terms of a methyl radical chain mechanism resulting from the pyrolytic initiation step CH4 CHg + H, followed by the exchange reaction CHa+ CD4-> CH3D + CD3.Several questions are apparent from a comparison of these two methane exchange reactions. Both studies are in the same temperature range, yet Bauer argues against the importance of pyrolysis in the exchange (1) (a) Support of this work by the National Science Foundation under Grant No. GP-23137 and also funds for equipment from NSF Departmental Science Development Program GU-2632 are gratefully acknowledged, (b) Paper presented in part at the Southwest