Decomposition of anthranil. Single pulse shock-tube experiments, potential energy surfaces and multiwell transition-state calculations. The role of intersystem crossing

The thermal decomposition of anthranil diluted in argon was studied behind reflected shock waves in a 2 in. i.d. pressurized driver single-pulse shock tube over the temperature range 825-1000 K and overall densities of approximately 3 x 10(-5) mol/cm(3). Two major products: aniline and cyclopentadiene carbonitrile (accompanied by carbon monoxide) and four minor products resulting from the decomposition were found in the postshock samples. They were, in order of decreasing abundance, pyridine, CH(2)=CHCN, HCN and CHC-CN, and comprised only a few percents of the overall product distribution. Quantum chemical calculations were carried out to determine the sequence of the unimolecular reactions that lead to the formation of cyclopentadiene carbonitrile and of phenylnitrene/phenylimine that are the precursors of aniline. They form aniline by reactions with traces of water impurities. To produce cyclopentadiene carbonitrile, two main processes must take place: CO elimination and ring contraction from a six- to a five-membered ring. It was shown that this can occur via two parallel pathways where CO elimination takes place prior to or following ring contraction. Singlet potential energy surfaces for all the elementary reactions that lead to the formation of cyclopentadiene carbonitrile and phenylnitrene/phenylimine were obtained. Their rate constants were calculated on the basis of the results of the quantum chemical calculations using transition-state theory. A kinetic scheme containing these reactions was constructed and multiwell calculations were performed to evaluate the mole percent of the products as a function of temperature. A very serious disagreement between the experimental results and the results of calculations showed that the singlet PESs could not account for the observed experimental rates. No other singlet PESs that lead to the formation of these products could be found. In view of this observation, attempts to find pathways that lead to the formation of cyclopentadiene carbonitrile and phenylnitrene/phenylimine on triplet surfaces were made. Such surfaces were found, and singlet <--> triplet intersystem crossing probabilities and crossing rate constants were calculated as well as the rate constants of all the elementary steps on the triplet surfaces. A reaction scheme was constructed and multiwell calculations were performed, including also the pathways on the singlet surfaces, to evaluate the mole percent of the products as a function of temperature. The agreement between the experimental results and these calculations was quite satisfactory.     

Embedding 1-Factorizations of K n in PG(2, 32)

1-Factorizations of the complete graph K _n embedded in a finite Desarguesian projective plane PG(2, q), q even, are hyperfocused arcs of size n. The classification of hyperfocused arcs is motivated by applications to 2-level secret sharing schemes. So far it has been done for q  ≤ 16, and for special types of hyperfocused arcs. In this paper the case q = 32 is investigated and the following two results are proven. (i) Uniqueness of hyperfocused 12-arcs, up to projectivities. (ii) Non-existence of hyperfocused 14-arcs.     

On the extendability of code isometries

A block codeC F ⁿ is calledmetrically rigid, if every isometry: CF ⁿ with respect to theHamming metric is extendable to an isometry of the whole spaceF ⁿ . The metrical rigidity of some classes of codes is discussed.Dedicated to Helmut Karzel on the occasion of his 70th birthdayResearch supported by the Russian Foundation of Fundamental Research (Grant no. 97-01-01104)Research supported by the Russian Foundation of Fundamental Research (Grants no. 96-01-01800, 97-01-01075)     

On perfect binary codes

Some results on perfect codes obtained during the last 6 years are discussed. The main methods to construct perfect codes such as the method of -components and the concatenation approach and their implementations to solve some important problems are analyzed. The solution of the ranks and kernels problem, the lower and upper bounds of the automorphism group order of a perfect code, spectral properties, diameter perfect codes, isometries of perfect codes and codes close to them by close-packed properties are considered.     

Una costruzione di una classe di 3-tessuti

In this paper a class of 3-nets is constructed and some properties of such nets are obtained.     

Precise and accurate compound-specific carbon and nitrogen isotope analysis of RDX by GC-IRMS

A new analytical method is presented for the compound-specific carbon and nitrogen isotope ratio analysis of a thermo-labile nitramine explosive hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) by gas chromatograph coupled to an isotope ratio mass spectrometer (GC-IRMS). Two main approaches were used to minimise thermal decomposition of the compound during gas chromatographic separation: programmed temperature vaporisation (PTV) as an injection technique and a high-temperature ramp rate during the GC run. δ¹⁵N and δ¹³C values of RDX measured by GC-IRMS and elemental analyser (EA)-IRMS were in good agreement within a standard deviation of 0.3‰ and 0.4‰ for nitrogen and carbon, respectively. Application of the method for the isotope analysis of RDX during alkaline hydrolysis at 50°C revealed isotope fractionation factors ε _carbon?=??7.8‰ and ε _nitrogen?=??5.3‰.