High-Pressure Study of Ion-Molecule Reactions in the Mixture of Carbon Tetrafluoride and Argon

Charge-exchange ion-molecule reactions of $Ar^+$ ions with $CF_4$ have been studied in the pressure range 1.33-39.99 Pa. A quadrupole mass spectrometer with a high-pressure ion source has been used for measuring gaseous ion-molecule reactions in the mixture of 1% $CF_4$ and 99% Ar. The fractional abundance $I_i//\sum I_i$ of the observed $CF_3^+$, $CF_2^+$ and argon ions has been determined as a function of the gas mixture pressure (at the values of the repeller electrode potentials $V_{R}$ ranging from 2 to 10 V)

Mass-Spectrometric Investigations of Silver Clusters

We report results of experimental studies on the silver clusters formation in laser desorption and matrix assisted laser desorption. Time-of-flight mass spectrometer was used to control process itself. Firstly, we investigated dependence of silver salts of variety chemical nature on formation of silver clusters. The most prominent was usage of organic silver salts (silver trifluoroacetate and silver benzoate). The biggest species obtained was $Ag_{45}^{+}$ (silver benzoate). Secondly, we examined influence of organic matrix (2,5-dihydroxybenzoic acid) on formation efficiency of silver clusters in matrix assisted laser desorption. In all cases we observed increase of silver clusters size

Viroids in Tahiti lime scions showing back cracking symptoms.

The so-called "quebra-galho" clone of Tahiti lime is very popular in Brazil, because the small size of the trees is suitable for high-density plantings. These Tahiti lime trees are easily recognized because they show bark-cracking symptoms, that have been claimed to be associated with "exocortis" infection. Viroid infection of three "quebra-galho" Tahiti lime trees from a farm near Araraquara in the state of São Paulo, Brazil, was assessed by Northern-blot hybridization using viroid-specific probes. Similarly, eight clones of Tahiti lime from different origins and available at Topara Nursery, near Chincha, Peru, were also tested for viroids. The four clones that displayed characteristic bark-cracking symptoms were found to be infected with Citrus exocortis viroid (CEVd), Hop stunt viroid (HSVd) and Citrus viroid III (CVd-III), whereas the clones that did not show bark-cracking symptoms were either viroid-free or infected only with CVd-III. A study is being conducted to establish if viroids, and in particular CEVd, are indeed the cause of "quebra-galho" bark cracking symptoms. Preliminary observations indicated that 2-yr old CEVd-infected lime trees at Moncada, Spain showed cracks.Disponível em: Acesso em: 11 mar. 2011