The reaction of an equimolar mixture of 28N2 and 30N2 (4% each) diluted by a mixture of Ne (80%) and Kr (12%) was studied over the temperature and density range 4700-5400 K and 2.5-2. X 10"6 mol cm"3, respectively. The reflected shock zone was sampled by a time-of-flight mass spectrometer at 20-µ8 intervals during typical observation periods of 0.5 ms. The product profiles were fit to the equation (1 -2/29) = exp(-fc'tz), where /29 is the mole fraction of 29N2. The time dependence z was determined to be 2.7 and the rate constants were best represented by the expression k = iO"1,24±0•54 exp(-138 ± 10/RT) µß"2•7. The inert gas dependence was assumed to be first order as reported from a previous single-pulse shock tube investigation. The rate constants from the single-pulse study were recalculated using z = 2.7 and were combined with the results herein. The resulting Arrhenius parameters span the extended temperature range 3200-5400 K: log A = 20.66 ± 0.08; E = 140 ± 1 kcal mol'1. The units of A are cm3 mol"1 s"2,7. The nonlinear time dependence for product formation confirms the earlier proposition of a mechanism which consists of a multistep sequence of reactions.
SynopsisThe conformations of the thyrotropin-releasing factor (TRF) and four analogs have been studied by the CNDOI2 molecular orbital method. The N"protonated tautomer of T R F is predicted to be the more stable of the two tautomeric forms; however, it is postulated that the Nf-tautomer possesses the most active minimum-energy conformation. The peptide backbone for the five compounds remains nearly constant. The conformations predicted from model fragments are very near to those found for the full compound.
The reaction of equimolar mixtures of hydrogen and bromine diluted by inert gases was studied in the reflected shock zone over a temperature and total density range of 1400-2000 K and 1.5 X lO-6^^X 10"6 *mol cm"3, respectively. Infrared emission from HBr passing through a narrow interference filter centered at 3.60 pm was recorded during observation periods typically of 500-pa duration. Conversion of the emission intensity traces to concentration-time data revealed nonlinear product growth for the low-temperature runs and near-linear product profiles at the higher temperatures. The individual experimental profiles were matched with the corresponding model calculations which employed a modern set of rate constants for the various elementary reactions comprising the atomic mechanism. The average percent deviation of 62 experiments from the calculated profiles was 5.4%.
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