Mutual Neutralization of NO

We have studied the mutual neutralization reaction of vibronically cold NO^{+} with O^{-} at a collision energy of ≈0.1 eV and under single-collision conditions. The reaction is completely dominated by production of three ground-state atomic fragments. We employ product-momentum analysis in the framework of a simple model, which assumes the anion acts only as an electron donor and the product neutral molecule acts as a free rotor, to conclude that the process occurs in a two-step mechanism via an intermediate Rydberg state of NO which subsequently fragments.

The mutual neutralization of hydronium and hydroxide.

Mutual neutralization of hydronium (H3O+) and hydroxide (OH-) ions is a very fundamental chemical reaction. Yet, there is only limited experimental evidence about the underlying reaction mechanisms. Here, we report three-dimensional imaging of coincident neutral products of mutual-neutralization reactions at low collision energies of cold and isolated ions in the cryogenic double electrostatic ion-beam storage ring (DESIREE). We identified predominant H2O + OH + H and 2OH + H2 product channels and attributed them to an electron-transfer mechanism, whereas a minor contribution of H2O + H2O with high internal excitation was attributed to proton transfer. The reported mechanism-resolved internal product excitation, as well as collision-energy and initial ion-temperature dependence, provide a benchmark for modeling charge-transfer mechanisms.

Erratum: State-Resolved Mutual Neutralization of Mg

This corrects the article DOI: 10.1103/PhysRevLett.128.033401.

High-precision electron affinity of oxygen.

Negative ions are important in many areas of science and technology, e.g., in interstellar chemistry, for accelerator-based radionuclide dating, and in anti-matter research. They are unique quantum systems where electron-correlation effects govern their properties. Atomic anions are loosely bound systems, which with very few exceptions lack optically allowed transitions. This limits prospects for high-resolution spectroscopy, and related negative-ion detection methods. Here, we present a method to measure negative ion binding energies with an order of magnitude higher precision than what has been possible before. By laser-manipulation of quantum-state populations, we are able to strongly reduce the background from photodetachment of excited states using a cryogenic electrostatic ion-beam storage ring where keV ion beams can circulate for up to hours. The method is applicable to negative ions in general and here we report an electron affinity of 1.461 112 972(87) eV for 16O.

State-Resolved Mutual Neutralization of Mg

We present experimental final-state distributions for Mg atoms formed in Mg^{+}+D^{-} mutual neutralization reactions at center-of-mass collision energies of 59±12 meV by using the merged-beams method. Comparisons with available full-quantum results reveal large discrepancies and a previously underestimated total rate coefficient by up to a factor of 2 in the 0-1 eV (<10^{4} K) regime. Asymptotic model calculations are shown to describe the process much better and we recommend applying this method to more complex iron group systems; data that is of urgent need in stellar spectral modeling.

Mutual neutralisation of O+ with O-: investigation of the role of metastable ions in a combined experimental and theoretical study.

The mutual neutralisation of O+ with O- has been studied in a double ion-beam storage ring with combined merged-beams, imaging and timing techniques. Branching ratios were measured at the collision energies of 55, 75 and 170 (± 15) meV, and found to be in good agreement with previous single-pass merged-beams experimental results at 7 meV collision energy. Several previously unidentified spectral features were found to correspond to mutual neutralisation channels of the first metastable state of the cation (O+(2Do), τ ≈ 3.6 hours), while no contributions from the second metastable state (O+(2Po), τ ≈ 5 seconds) were observed. Theoretical calculations were performed using the multi-channel Landau-Zener model combined with the anion centered asymptotic method, and gave good agreement with several experimentally observed channels, but could not describe well observed contributions from the O+(2Do) metastable state as well as channels involving the O(3s 5So) state.

Investigation into the vibrational yield of OH products in the OH+H+H channel arising from the dissociative recombination of H(3)O(+).

The vibrational population of the hydroxyl radical, OH, formed in the OH+H+H channel arising from the dissociative recombination of the hydronium ion, H(3)O(+), has been investigated at the storage ring CRYRING using a position-sensitive imaging detector. Analysis shows that the OH fragments are predominantly produced in the v=0 and v=1 states with almost equal probabilities. This observation is in disagreement with earlier FALP experiments, which reported OH(v=0) as the dominant product. Possible explanations for this difference are discussed.

Operating a triple stack microchannel plate-phosphor assembly for single particle counting in the 12-300 K temperature range.

An assembly consisting of a stack of three microchannel plates (MCPs) and a phosphor screen anode has been operated over the temperature range from 300 to 12 K. We report on measurements at 6.4 kHz (using an alpha source) and with dark counts only (15 Hz). Without any particle source, the MCP bias current decreased by a factor of 2.1 x 10(3) when the temperature was lowered from 300 to 12 K. Using the alpha source, and a photomultiplier tube (PMT) to monitor the phosphor screen anode, we first observed an increase in the decay time of the phosphor from 12 to 45 mus when the temperature was decreased from 300 to 100 K while the decay time then decreased and reached a value of 5 mus at 12 K. The pulse height distribution from the PMT was measured between 300 and 12 K and shows a spectrum typical for a MCP phosphor setup at 300 K and 12 K but is strongly degraded for intermediate temperatures. We conclude that the present MCP-phosphor detector assembly is well suited for position-sensitive particle counting operation at temperatures down to at least 12 K even for count rates beyond 6 kHz. This result is crucial and an important part of ongoing developments of new instrumentation for investigations of, e.g., interactions involving complex molecular ions with internal quantum state control.

Description of a technique for evaluation of three-dimensional shape alterations in soft tissue after intra oral bone reconstruction.

Equipment from GFMesstechnik, Germany, for three-dimensional (3D) measurements of topography alterations was tested in an intra oral situation. A patient with previous loss of tooth 21 due to trauma planned for local bone grafting procedure together with a titanium mesh and later implant insertion was signed as a trial. Pre- and postoperative measurements of the buccal contour in maxillary anterior region were performed with the 3D equipment and the pictures were evaluated in a software programme. The evaluation showed ability to reproduce numerical volume changes in the buccal soft tissue in the operated area. The contour changes can be displayed as a diagram change as well, with possibility to make numerical calculations. We believe this is an excellent system to use in long-term follow-ups of the soft tissue changes after intra oral reconstructive procedures. The procedure is a rapid, accurate, and harmless procedure and can be performed directly on the patient.

Effect of vitamin E on autolysis and sporulation of Aspergillus nidulans.

The morphologic and physiologic effects of vitamin E, a powerful antioxidant, on the autolysis and sporulation of Aspergillus nidulans FGSC26 were studied. In carbon-depleted submerged cultures, reactive oxygen species (ROS) accumulated in the cells and, concomitantly, progressing autolysis was observed, which was characterized by decreasing dry cell masses and pellet diameters as well as by increasing extracellular chitinase activities. Vitamin E supplemented at a concentration of 1 g/L hindered effectively the intracellular accumulation of ROS, the autolytic loss of biomass, the disintegration of pellets, and the release of chitinase activities. In surface cultures, vitamin E inhibited autolysis of both A. nidulans FGSC26 and a loss-of-function FlbA autolytic phenotype mutant. In addition, supplementation of the culture medium with this antioxidant also had a negative effect on the sporulation of strain FGSC26 and the FadAG203R hypersporulating phenotype mutant. These results suggest that accumulation of ROS was involved in the initiation of both sporulation and autolysis in this filamentous fungus, but that FadA/FlbA signaling was not involved in this vitamin E-dependent regulation. Vitamin E can be recommended as a supplement in fermentations in which the disintegration of pellets and gross autolysis should be avoided.

Influence of fadAG203R and deltaflbA mutations on morphology and physiology of submerged Aspergillus nidulans cultures.

Morphologic and physiologic changes taking place in carbon-limited submerged cultures of Aspergillus nidulans deltaflbA and fadAG203R strains were studied. Loss-of-function mutation of the flbA gene resulted in an altered germination with unusually thick germination tubes, "fluffy" pellet morphology, as well as a reduced fragmentation rate of hyphae during autolysis. In the fadAG203R mutant strain, conidiophores formed in the stationary phase of growth, and the size of pellets shrank considerably. There were no significant differences in the generation of reactive oxygen species (ROS) and in the specific catalase and superoxide dismutase activities by the tested mutants and the appropriate parental strains. Therefore, the participation of ROS or antioxidative enzymes in FadA/FlbA signaling pathways seems to be unlikely in submerged cultures. On the other hand, earlier increases in the extracellular protease and ammonia production were recorded with the deltaflbA strain, whereas the protease and ammonia production of the fadAG203R mutant lagged behind those of the wild-type strains. Similar changes in the time courses of the induction of gamma-glutamyltranspeptidase and the degradation of glutathione were observed. These results suggest that FadA/FlbA signaling may be involved in the mobilization of protein and peptide reserves as energy sources during carbon starvation.

Deletion of a lectin gene does not affect the phenotype of the nematode-trapping fungus Arthrobotrys oligospora.

A number of filamentous fungi are known to produce high levels of saline-soluble and low-molecular-mass lectins. The function of these proteins are not clear but it has been proposed that they are involved in storage of nutrients, development, recognition of other organisms, and defense reactions. A gene encoding such a lectin (AOL) was deleted in the nematode-trapping fungus Arthrobotrys oligospora by homologous recombination. The deletion mutants did not express any hemagglutinating activity or protein cross-reacting with AOL antibodies. There were no significant differences between the DeltaAOL and wild-type strains in spore (conidia) germination, saprophytic growth, and pathogenicity. Furthermore, there was no significant difference in the growth and reproduction of collembolan feeding on the various strains of A. oligospora. Thus either the previous proposed functions of AOL are not correct, or the fungus can compensate for the absence of the lectin by expressing other proteins with similar function(s) as AOL.

A cytoplasmic lectin produced by the fungus Arthrobotrys oligospora functions as a storage protein during saprophytic and parasitic growth.

It was recently shown that the nematode-infecting fungus Arthrobotrys oligospora contains a saline-soluble lectin (designated AOL) that is a member of a novel family of fungal lectins sharing similar primary sequences and binding specificities. During saprophytic growth in liquid cultures, levels of AOL and AOL mRNA were found to vary depending on the growth phase of the mycelium and the carbon/nitrogen (C/N) ratio of the medium. AOL was not detected in young mycelium. In older mycelium (stationary growth phase) grown in media with low C/N ratios (1 or 6), AOL comprised 5-20% of the total amount of saline-soluble proteins present in the mycelium. Neither the lectin nor its transcript was detected in mycelia grown in medium with higher C/N ratios (≥150). Under conditions of nitrogen starvation, AOL was preferentially degraded in relation to the total amount of saline-soluble proteins present in the mycelium. During the infection of nematodes, the level of AOL protein and AOL mRNA increased significantly once the nematodes had been penetrated and digested. Large amounts of AOL accumulated in the trophic hyphae growing inside the nematode as visualized by immunofluorescence microscopy. Later, AOL labelling was detected outside the digested nematodes, preferentially in strands of aggregated hyphae and in newly developed trap cells. Electron microscopy showed that AOL was localized to the cytoplasm and the nucleus of both vegetative mycelium and trap cells, and in the trophic hyphae growing inside the infected nematodes. These results indicate that AOL functions as a storage protein during both saprophytic and parasitic growth.