The photodissociation dynamics of the ethyl radical C(2)H(5) has been investigated by velocity map imaging. Ethyl was produced by flash pyrolysis from n-propyl nitrite and excited to the à (2)A(') (3s) Rydberg state around 250 nm. The energetically most favorable reaction channel in this wavelength region is dissociation to C(2)H(4) (ethene) + H. The H-atom dissociation products were ionized in a [1+1(')] process via the 1s-2p transition. The observed translational energy distribution is bimodal: A contribution of slow H-atoms with an isotropic angular distribution peaks at low translational energies. An expectation value for the fraction of excess energy released into translation of = 0.19 is derived from the data, typical for statistical dissociation reactions. In addition, a fast H-atom channel is observed, peaking around 1.8 eV. The latter shows an anisotropic distribution with β = 0.45. It originates from a direct dissociation process within less than a rotational period. Time-delay scans with varying extraction voltages indicate the presence of two rates for the formation of H-atoms. One rate with a sub-nanosecond time constant is associated with H-atoms with large translational energy; a second one with a time constant on the order of 100 ns is associated with H-atoms formed with low translational energy. The data confirm and extend those from previous experiments and remove some inconsistencies. Possible mechanisms for the dissociation are discussed in light of the new results as well as previous ones.

Two C(9)H(7) isomers, 1-phenylpropargyl and 3-phenylpropargyl, have been studied by IR/UV double resonance spectroscopy in a free jet. The species are possible intermediates in the formation of soot and polycyclic aromatic hydrocarbons (PAH). The radicals are generated by flash pyrolysis from the corresponding bromides and ionized at 255-297 nm in a one-color, two-photon process. Mid-infrared radiation between 500 and 1800 cm(-1) is provided by a free electron laser (FEL). It is shown that the two radicals can be distinguished by their infrared spectra. In addition, we studied the dimerization products originating from the phenylpropargyl self-reaction. We utilize the fact that the pyrolysis tube can be considered to be a flow reactor permitting us to investigate the chemistry in such a thermal reactor. Dimerization of phenylpropargyl produces predominately species with m/z = 228 and 230. A surprisingly high selectivity has been found: The species with m/z = 230 is identified to be para-terphenyl, whereas m/z = 228 can be assigned to 1-phenylethynyl-naphthalene. The results allow to derive a mechanism for the dimerization of phenylpropargyl and suggest hitherto unexplored pathways to the formation of soot and PAH.

The bacterial community in the gut of the earthworm Lumbricus terrestris was analyzed by whole-cell hybridization with 16S rRNA targeted oligonucleotide probes. Whole-cell hybridization protocols using fluorescence-, peroxidase-, or digoxigenin-labeled oligonucleotide probes facilitated detection of significant fractions of bacterial cells stained with 4′,6-diamidino-2-phenylindole (DAPI) in the fore-, mid-, and hind-gut and cast of the earthworm. The application of peroxidase- and digoxigenin-labeled probes, however, was hampered by several methodological drawbacks: the requirement of enzymatic permeabilization, the diffuse images of stained cells, and the incompatibility with DAPI staining used as control. Quantitative analysis of the bacterial community was also influenced by its considerable variability in different individual earthworms. Though the number of bacteria detected by DAPI staining as well as by whole-cell hybridization with the fluorescent eubacterial probe Eub338 generally showed a significant increase in the number of bacteria towards the end of the gut, a decrease in bacterial numbers could be found in some earthworms. In situ analysis of the bacterial community in the fore-, mid-, and hind-gut of one individual earthworm by whole-cell hybridization with the fluorescent eubacterial probe Eub338 recorded 15, 30, and 25% of DAPI-stained bacteria, respectively. In the cast 37% of the bacteria were detected. Similar to counts obtained by DAPI and by whole-cell hybridization with probe Eub338, the number of bacteria belonging to the α-, β-, and γ-subgroups of proteobacteria increased significantly towards the end of the gut and remained high in the cast. While the most significant difference in the counts of bacteria belonging to the α-subgroup was obtained between the hind-gut and cast, bacterial populations of the β- and γ- subgroups of proteobacteria increased most prominently between the fore- and hind-gut.Key words: digoxigenin, fluorescent probes, in situ detection, Lumbricus terrestris, rRNA, whole-cell hybridization.

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The borylene complex [(OC)(5)Cr=B=N(SiMe(3))(2)] has been investigated by using threshold photoelectron-photoion coincidence spectroscopy with synchrotron radiation. The ionization energy of the parent complex and the 0 K appearance energies of the sequential CO loss channels have been determined. The derived bond-dissociation energies are used to discuss bonding and energetics in this compound.