Thermal and photochemical decomposition of a styrene-oxygen copolymer

En este trabajo se estudia la ruptura térmica y fotoquímica de un poli-peróxido de estireno de peso molecular 2100. A partir de medidas de la velocidad de polimerización del estireno fotosensitizado por el poli-peróxido se puede concluir que la recombinación primaria es de 0.66. Los parámetros de Arrhenius obtenidos para la ruptura térmica son considerablemente menores que los obtenidos para la ruptura del ditert-butil peróxido

Unexpected solvent isotope effect on the triplet lifetime of methylene blue associated to cucurbit[7]uril

[EN] Methylene blue shows an isotope dependent triplet lifetime that is 50% longer in D2O compared with H2O as a result of electronic-to-vibrational relaxation. The effect is enhanced when the dye is bound to curcubit[7]uril due to a combination of restricted mobility and a unfavorable vibrational coupling.This work was supported by NSERC-Canada. M. G. B thanks the Spanish Ministry of Science and Innovation for a post-doctoral contract. E. A. Acknowledges Becas Chile and the University of Ottawa for postdoctoral fellowships. We also thank Michel Grenier for his help on the time resolved measurements.Alarcón, E.; González Béjar, M.; Montes Navajas, PM.; García Gómez, H.; Lissi, E.; Scaiano, JC. (2012). Unexpected solvent isotope effect on the triplet lifetime of methylene blue associated to cucurbit[7]uril. Photochemical & Photobiological Sciences. 11(2):269-273. doi:10.1039/c1pp05227fS269273112N. J. Turro , V.Ramamurthy and J. 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Study on cosmogenic activation above ground for the DarkSide-20k project

The activation of materials due to the exposure to cosmic rays may become an important background source for experiments investigating rare event phenomena. DarkSide-20k is a direct detection experiment for galactic dark matter particles, using a two-phase liquid argon time projection chamber filled with 49.7 tonnes (active mass) of Underground Argon (UAr) depleted in 39Ar. Here, the cosmogenic activity of relevant long-lived radioisotopes induced in the argon and other massive components of the set-up has been estimated; production of 120 t of radiopure UAr is foreseen. The expected exposure above ground and production rates, either measured or calculated, have been considered. From the simulated counting rates in the detector due to cosmogenic isotopes, it is concluded that activation in copper and stainless steel is not problematic. Activation of titanium, considered in early designs but not used in the final design, is discussed. The activity of 39Ar induced during extraction, purification and transport on surface, in baseline conditions, is evaluated to be 2.8% of the activity measured in UAr from the same source, and thus considered acceptable. Other products in the UAr such as 37Ar and 3H are shown to not be relevant due to short half-life and assumed purification methods

Kinetics and mechanism of the reaction of a nitroxide radical (tempol) with a phenolic antioxidant

In the absence of redox-active transition metal ions, the removal of Tempol by Trolox occurs by a simple bimolecular reaction that, most probably, involves a hydrogen transfer from phenol to nitroxide. The specific rate constant of the process is small (0.1 M-1 s-1). Metals can catalyze the process, as evidenced by the decrease in rate observed in the presence of diethylenetriaminepentaacetic acid (DTPA). Furthermore, addition of Fe(II) (20 μM ferrous sulfate and 40 μM EDTA) produces a noticeable increase in the rate of Tempol consumption

Oxidation of carbon monoxide by t-butoxy-radicals

The study of the pyrolysis of di-t-butyl peroxide in the presence of carbon monoxide allows an evaluation of the rate constant for the oxidation of carbon monoxide by t-butoxy-radicals