Formation of polycyclic aromatic hydrocarbons from bimolecular reactions of phenyl radicals at high temperatures.

The self-reaction of the phenyl radical is one of the key reactions in combustion chemistry. Here we study this reaction in a high-temperature flow reactor by IR/UV ion dip spectroscopy, using free electron laser radiation as mid-infrared source. We identified several major reaction products based on their infrared spectra, among them indene, 1,2-dihydronaphthalene, naphthalene, biphenyl and para-terphenyl. Due to the structural sensitivity of the method, the reaction products were identified isomer-selectively. The work shows that the formation of indene and naphthalene, which was previously considered to be evidence for the HACA (hydrogen abstraction C2H2 addition) mechanism in the formation of polycyclic aromatic hydrocarbons and soot can also be understood in a phenyl addition model.

Tuning of the dimensional linkage from the complex to the framework by thermal conversion in the system Fe/Cl/piperazine.

An attempt to control the three structural features linkage, structural dimensionality and coordination mode is presented for the combination of Fe(II) and Fe(III) chlorides together with the ditopic ligand piperazine (pipz). Thermal conversion of small units like complexes into highly aggregated structures such as coordination polymers is demonstrated for the framework formation of ∞³[Fe(II)Cl2(pipz)] starting from both FeCl2 and FeCl3. Depending on the oxidation state of iron, different reaction paths and metastable products are observed. Iron(II)chloride reacts with piperazine to form the previously unknown 2-dimensional network, ∞²[Fe(II)2Cl4(pipz)3]·pipz, which can be thermally converted into the 3-dimensional framework at elevated temperatures by release of piperazine. The use of iron(III)chloride starts with an internal redox reaction giving the divalent complex [Fe(II)Cl3(Hpipz)(pipz)] in the first step, followed by thermal conversion yielding the framework ∞³[Fe(II)Cl2(pipz)] and the salt [Fe(II)Cl3(Hpipz)(pipz)](Hpipz)Cl2. Both thermal conversion mechanisms were further investigated by in situ IR-spectroscopy, differential thermal analysis and thermogravimetry.

Method of Measuring Diffuse RMS Granularity.

The rms granularity values normally produced by an optical scanner are in terms of semispecular instrument density. It is shown that these semispecular values can be converted to a diffuse density basis by dividing by a quantity q that is defined as the ratio of the instrument density of the sample to the diffuse density. The q factor has been measured by two methods, one of which is convenient for use in the routine measurement of diffuse granularity with existing equipment. It has been found that, except at very low density levels, the q of a given material varies only slightly as the diffuse density changes. It does, however, increase significantly as the numerical aperture of the optical system decreases. When a range of samples is measured, maximum values of q occur at moderate values of sample granularity.