Photoinduced ion-molecule reactions of primary ions occurring in the ethylamines and propylamine have been investigated in the pressure range 1-20 mTorr using a Kr resonance lamp (10.03 and 10.6 eV) as the excitation source. Thermal rate constants (T = 298°K) have been determined for the reactions R3_"+NH" + R3-"NH" R3_"+NHn+i + R3_nNH"(-H) (fci) and R2_n(CH2)+NHn + R3-nNHn -R2-"(CH2)NHn(-H) + R3-n+NHn+i (k2) where = 0,1, and 2 for R = C2H5 and = 2 for R = C3H7. For the ethylamines the values for ki were found to be 18.3, 12.5, and 7.05 X 10-10 cm3 sec-1 and for k2, 19.7, 13.6, and 1.28 X 10-1°cm3 sec-1 for = 2,1, and 0, respectively. For propylamine the corresponding values for ki and k2 are 15.6 and 22.4 X 10~10 cm3 sec-1. The values of hi are slightly less than those previously reported for the methylamines and are shown to be consistent with the predictions for an ion-induced dipole model for ion-molecule reactions which assumes a collision complex in which the polar molecule is aligned with the ion and takes into account intrinsic differences in the N-H and C-H hydrogen-transfer rates. The observed change in k2 with increasing ethyl substitution is explained on the basis of the structure of the primary ion, R2_"(CH2)+NH".
The rate law for the production of HCN over the temperature range 1850-2900 K was established by recording the time-dependent infrared emission from this species at 3.0 pm in the reflected shock zone. Four mixtures of C1CN and H2 dilute in argon, differing in the ratio of initial reactant concentrations and initial shock pressures, were studied in order to determine the various order dependencies. The formation of the product was in all experiments observed to be nonlinear with respect to reaction time. The data were fit to the equation 1 -/HCN//HCN,max = expH[ClCN]o0'6[H2]00'1[Ar]0'4í2), where k = 102L8±°•06 exp(-70.3 ± 0.6/flT) cm3 mol"1 s"2. The units for the activation energy are kcal mol"1. Experiments in which the reflected shock zone was analyzed with a time-of-flight mass spectrometer revealed the products to be HCN, HC1, and C2N2. Computer calculated profiles of HCN using a 14 step atomic mechanism with available literature rate constants failed to reproduce the experimental profiles.
A complementary shock tube system was used to study dilute mixtures of carbon dioxide and hydrogen in a 1:5 ratio reacting behind reflected shock waves to produce water and carbon monoxide over the temperature range 2275-3860 K. One shock tube was outfitted to record simultaneously the infrared emissions from water and carbon dioxide through interference filters centered at 3.8 and 4.2 p, respectively. In order to minimize overlapping emissions, D2 was employed instead of H2. The formation of D2O exhibited quadratic dependence with respect to reaction time. The appearance of CO2 emission 4served primarily to mark time zero for the reaction and to establish the position of equilibrium. Argon was the inert diluent. The starting reactant percentages and the reflected shock zone pressure were varied for the purpose of determining the order dependencies for D2 and the total gas density. The second shock tube was connected to a time-of-flight mass spectrometer which recorded the histories of reactants, products, and intermediates. One notable feature of the TOF experiments was the detection of a small peak at m/e 29 corresponding to the HCO radical which was formed at times previous to significant CO production when H2 was used as a reactant. Runs performed on a, CO2-D2 mixture under similar conditions revealed the presence of DCO. The mole fraction for water formation from both shock tubes was fit to the expression (1 -/D2o//b2o,eq) * exp{-k [D2]0,3[M]0,7t2), where k = l02o o±o'2 exp(-81.4 ± 2.3/RT) cm3 mol-1 s-2. The units for the activation energy are kcal mol-1. Product profiles computed from a selection of literature rate constants making up an atomic mechanism did not compare favorably with the experimental results. The .possibility of a mechanism involving vibrational excitation of the reactants prior to transition state formation is discussed.
The metathetical reaction, C2N2 + H2 <=r 2HCN, has been studied by shocking equimolar amounts of the reactants in the presence of an inert gas diluent over the temperature range 1850-2650°K. A complementary shock tube facility was utilized to obtain the data from the reflected shock zone by recording the infrared emission of HCN and the time-resolved mass spectra at m/e 27 (HCN) and 52 (C2N2). The total density variation was 1.8-4.4 X 10~8 mol/cm3. Observation times were typically 500 psec during which period an equilibrium condition was established for the higher temperature experiments. The growth of the mole fraction of HCN, /hcn, was found to be a nonlinear function of time and to depend upon the inert gas concentration, [M]. The data from the two independent techniques of infrared emission and mass spectrometry were fitted to the bimolecular rate expression that includes the back reaction, In |[(X -4)/Hcn -(X + 2X1/2)]/[(X-4)/HCn -(X -where the forward rate constant is given by fci = 102®-3S±0-21 exp(-61,610 ± 2010/RT) cm3 mol-1 sec-2 [M]-°-75. These results rule out the direct bimolecular reaction. This complex reaction is discussed in terms of an atomic mechanism and a mechanism involving vibrationally excited species. Experiments on an equimolar mixture of cyanogen and deuterium revealed a lowering of the preexponential factor in reasonable agreement with that predicted from the square root of the inverse ratio of reduced masses.
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