Valence shell threshold photoelectron spectroscopy of C3Hx (x = 0-3).

We present the photoelectron spectra of C3Hx (x = 0-3) formed in a microwave discharge flow-tube reactor by consecutive H abstractions from C3H4 (C3Hx + F → C3Hx-1 + HF (x = 1-4)), but also from F + CH4 schemes by secondary reactions. The spectra were obtained combining tunable VUV synchrotron radiation with double imaging electron/ion coincidence techniques, yielding mass-selected threshold photoelectron spectra. The obtained results complement not only existing ones, but for the first time the photoelectron spectra of C3, cyclic and linear C3H (c,l-C3H) as well as of the excited states of C3H3 are reported. In the case of c-C3H, l,t-C3H2 and C3H3, Franck-Condon simulations have been performed in order to assign the vibrational structure. The adiabatic ionization energies of these radicals are reported and compared to ab initio calculated values as well as to theoretical values using known enthalpies of formation.

Compact FTICR Mass Spectrometry for Real Time Monitoring of Volatile Organic Compounds.

In this paper, we present a compact Fourier transform ion cyclotron resonance mass spectrometer (FTICR-MS) designed for real time analysis of volatile organic compounds (VOCs) in air or in water. The spectrometer is based on a structured permanent magnet made with NdFeB segments. Chemical ionization is implemented inside the ICR cell. The most widely used reaction is the proton transfer reaction using H3O⁺ precursor ions, but other ionic precursors can be used to extend the range of species that can be detected. Complex mixtures are studied by switching automatically from one precursor to another. The accuracy obtained on the mass to charge ratio (Δm/z 5 × 10−3), allows a precise identification of the VOCs present and the limit of detection is 200 ppb without accumulation. The time resolution is a few seconds, mainly limited by the time necessary to come back to background pressure after the gas pulses. The real time measurement will be illustrated by the monitoring of VOCs produced during the thermal degradation of a polymer and by an example where three different precursor ions are used alternatively to monitor a gas sample.

Effects of collision energy and vibrational excitation of CH3+ cations on its reactivity with hydrocarbons: But-2-yne CH3CCCH3 as reagent partner.

The methyl carbocation is ubiquitous in gaseous environments, such as planetary ionospheres, cometary comae, and the interstellar medium, as well as combustion systems and plasma setups for technological applications. Here we report on a joint experimental and theoretical study on the mechanism of the reaction CH3+ + CH3CCCH3 (but-2-yne, also known as dimethylacetylene), by combining guided ion beam mass spectrometry experiments with ab initio calculations of the potential energy hypersurface. Such a reaction is relevant in understanding the chemical evolution of Saturn's largest satellite, Titan. Two complementary setups have been used: in one case, methyl cations are generated via electron ionization, while in the other case, direct vacuum ultraviolet photoionization with synchrotron radiation of methyl radicals is used to study internal energy effects on the reactivity. Absolute reactive cross sections have been measured as a function of collision energy, and product branching ratios have been derived. The two most abundant products result from electron and hydride transfer, occurring via direct and barrierless mechanisms, while other channels are initiated by the electrophilic addition of the methyl cation to the triple bond of but-2-yne. Among the minor channels, special relevance is placed on the formation of C5H7+, stemming from H2 loss from the addition complex. This is the only observed condensation product with the formation of new C-C bonds, and it might represent a viable pathway for the synthesis of complex organic species in astronomical environments and laboratory plasmas.

Is the Reaction of C3N(-) with C2H2 a Possible Process for Chain Elongation in Titan's Ionosphere?

The reaction of C3N(-) with acetylene was studied using three different experimental setups, a triple quadrupole mass spectrometer (Trento), a tandem quadrupole mass spectrometer (Prague), and the "CERISES" guided ion beam apparatus at Orsay. The process is of astrophysical interest because it can function as a chain elongation mechanism to produce larger anions that have been detected in Titan's ionosphere by the Cassini Plasma Spectrometer. Three major products of primary processes, C2H(-), CN(-), and C5N(-), have been identified, whereby the production of the cyanide anion is probably partly due to collisional induced dissociation. The formations of all these products show considerable reaction thresholds and also display comparatively small cross sections. Also, no strong signals of anionic products for collision energies lower than 1 eV have been observed. Ab initio calculations have been performed to identify possible pathways leading to the observed products of the title reaction and to elucidate the thermodynamics of these processes. Although the productions of CN(-) and C5N(-) are exoergic, all reaction pathways have considerable barriers. Overall, the results of these computations are in agreement with the observed reaction thresholds. Due to the existence of considerable reaction energy barriers and the small observed cross sections, the title reaction is not very likely to play a major role in the buildup of large anions in cold environments like the interstellar medium or planetary and satellite ionospheres.

State-Selected Reactivity of Carbon Dioxide Cations ( CO 2 + ) With Methane.

The reactivity of CO 2 + with CD4 has been experimentally investigated for its relevance in the chemistry of plasmas used for the conversion of CO2 in carbon-neutral fuels. Non-equilibrium plasmas are currently explored for their capability to activate very stable molecules (such as methane and carbon dioxide) and initiate a series of reactions involving highly reactive species (e.g., radicals and ions) eventually leading to the desired products. Energy, in the form of kinetic or internal excitation of reagents, influences chemical reactions. However, putting the same amount of energy in a different form may affect the reactivity differently. In this paper, we investigate the reaction of CO 2 + with methane by changing either the kinetic energy of CO 2 + or its vibrational excitation. The experiments were performed by a guided ion beam apparatus coupled to synchrotron radiation in the VUV energy range to produce vibrationally excited ions. We find that the reactivity depends on the reagent collision energy, but not so much on the vibrational excitation of CO 2 + . Concerning the product branching ratios ( CD 4 + / CD 3 + /DOCO+) there is substantial disagreement among the values reported in the literature. We find that the dominant channel is the production of CD 4 + , followed by DOCO+ and CD 3 + , as a minor endothermic channel.

Micorrização e atividade microbiana de um solo cultivado com coentro e camomila / Micorrización y actividad microbiana de suelo cultivado con manzanilla y cilantro / Mycorrhization and microbial activity from a soil cultivated with coriander and chamomile

Fungos micorrízicos arbusculares (FMAs), entre outros micro-organismos do solo, desempenham papel fundamental no crescimento de plantas. O objetivo deste trabalho foi avaliar a densidade de esporos e a colonização radicular por FMAs em solos cultivados com coentro (Coriandrum sativum L.) e camomila (Matricaria chamomilla L.), bem como a atividade microbiana do solo medida por meio da respiração basal do solo (RBS) e matéria orgânica do solo (MOS). Foram coletadas quatro amostras de solo e raízes no horto medicinal da Universidade Paranaense, Umuarama-PR e de uma área adjacente de mata nativa. A densidade de esporos de FMAs no solo cultivado com camomila foi três vezes maior (44,2 esporos g?1 solo) do que no solo cultivado com coentro (16,8 esporos g?1 solo) e de mata (9,9 esporos g?1 solo). A colonização radicular por FMAs não diferiu significativamente. O solo da mata apresentou maior atividade microbiana (2,0 mg CO2 kg?1 solo h?1) comparado com os solos cultivados com camomila e coentro (1,56 e 1,13 mg CO2 kg?1 solo h?1, respectivamente). O mesmo comportamento foi observado com a MOS. Conclui-se que o solo cultivado com camomila apresentou maior densidade de esporos de FMAs, comparado com os solos da mata e coentro. A maior atividade microbiana no solo da mata é possivelmente em virtude do maior fornecimento de matéria orgânica e ciclagem do carbono.

The arbuscular mycorrhizal fungi (AMFs), among other soil microbial microrganisms, has a fundamental role in plant growth. The objective of this study is to evaluate the spore density and root colonization by AMFs and microbial activity measuring basal soil respiration (BSR) and soil organic matter (SOM) from soil and root collected from coriander (Coriandrum sativum L.) and chamomile (Matricaria chamomilla L.). Four soil and root samples were collected in a medicinal botanical garden at the Paranaense University, Umuarama ? PR, and soil samples from a nearby forest was used as control. The spore density of AMF in the soil differed significantly among treatments. In the soil under chamomile, the amount of spores found was over three-fold the amount of spores found in relation to forest and soil cultivated with coriander, but soil under coriander and forest did not differ significantly. The assessment of root colonization by AMF was not significantly different among treatments. In soil from the forest, a higher soil microbial activity (2.0 mg CO2 kg?1 solo h?1) was found when compared to soil cultivated with chamomile and coriander (1.56 and 1.13 mg CO2 kg?1 soil h?1, respectively). The same behavior was observed with SOM. It can be concluded that the soil cultivated with chamomile showed higher spore density of AMF compared to coriander and forest. A higher forest soil microbial activity is possibly due to a major input of SOM e carbon cycling.

Hongos micorrízicos arbusculares (HMA) y otros micro-organismos del suelo, desempeñan papel fundamental en el crecimiento de las plantas. El objetivo de este estudio fue evaluar la densidad de esporas y la colonización de las raíces por HMAs en suelos cultivados con cilantro (Coriandrum sativum L.) y manzanilla (Matricaria chamomilla L.), así como la actividad microbiana del suelo medido por medio de la respiración basal del suelo (RBS) y materia orgánica del suelo (MOS). Se colectó cuatro muestras de suelo y raíces en el jardín de plantas medicinales de la Universidad Paranaense, Umuarama - PR, y de una zona adyacente de mata nativa. La densidad de esporas de HMAs en el suelo cultivado con manzanilla fue tres veces mayor (44,2 esporas g-1 de suelo) que en el suelo cultivado con cilantro (16,8 esporas g-1 de suelo) y de mata (9,9 esporas g-1 suelo). La colonización radicular por HMAs no difirió significativamente. El suelo de la mata presentó mayor actividad microbiana (2,0 mg CO2 kg-1 suelo h-1) en comparación con los suelos cultivados con manzanilla y cilantro (1,56 y 1,13 mg CO2 kg-1 suelo h-1, respectivamente). El mismo comportamiento se observó con el MOS. Se concluye que el suelo cultivado con manzanilla presenta mayor densidad de esporas de AMFs, en comparación con los suelos de mata y cilantro. La mayor actividad microbiana en el suelo de mata es posiblemente en virtud de mayor oferta de materia orgánica y el ciclo del carbono.