One-electron redox reactions of three bis(alkyl carboxylic acid) selenide (SeC) derivatives viz., seleno bis(butanoic acid) (SeBA), seleno bis(propanoic acid) (SePA) and seleno bis(ethanoic acid) (SeEA), were carried out in aqueous solutions using nanosecond pulse radiolysis and the resultant transients were detected by absorption spectroscopy. SeC reacted with cOH radicals to form hydroxyl selenouranyl radicals (pSerOH) which subsequently gave different transient species, like the selenium centered radical cation (SeCc + ), dimer radical cation (pSerSe) + , or a selenium-carboxyl oxygen stabilized monomer radical (pSerO). The relative yield of these transient species depended on pH, concentration of SeC and position of the carboxylate functional group. SeEA and SeBA gave exclusively (pSerSe) + absorbing at 490 nm, while in the case of SePA, along with (pSerSe) + , (pSerO) was also formed. The stability of (pSerSe) + was estimated in terms of the equilibrium constant and was in the order SeBA > SeEA > SePA. Secondary electron transfer reactions of the transients were performed with 2,2 0 -azinobis(3-ethylbenzthiazoline-6-sulphonic acid), thionine and methyl viologen. The study showed that SeCc + undergoes decarboxylation with the formation of the corresponding a-(alkylseleno)alkyl radical and the yield of CO 2 formed was in the order SeEA < SeBA < SePA. The formation of a stabilised monomer radical cation in SePA is responsible for its lower yield of CO 2 and the same is reflected in its higher free radical scavenging antioxidant activity, established by comparing the rate constants for scavenging of peroxyl radicals.

A high-voltage pulse-slicer unit with variable pulse duration has been developed and integrated with a 7 MeV linear electron accelerator (LINAC) for pulse radiolysis investigation. The pulse-slicer unit provides switching voltage from 1 kV to 10 kV with rise time better than 5 ns. Two MOSFET based 10 kV switches were configured in differential mode to get variable duration pulses. The high-voltage pulse has been applied to the deflecting plates of the LINAC for slicing of electron beam of 2 μs duration. The duration of the electron beam has been varied from 30 ns to 2 μs with the optimized pulse amplitude of 7 kV to get corresponding radiation doses from 6 Gy to 167 Gy.

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Dependency of H2 production and frequency gaps with working frequency, applied electric fields, discharge gas-gap (GG), and central electrode materials in Ar-moisture dielectric barrier discharge (DBD) non-thermal plasma is presented. H2 production during the transformation of moisture in an Ar carrier having 100% relative humidity employing DBD is monitored by gas chromatography with a thermal conductivity detector. Coaxial cylindrical reactors with an outer Pyrex tube (common for all reactors) accompanied by two different categories of central electrodes [Pyrex in double dielectric (DD) and bare metal, such as stainless steel or aluminum or copper (Cu) in single dielectric (SD) of different GGs], are used. A high-frequency (4–30 kHz) ac power supply is employed for plasma as well as H2 generations. Dissipated powers in reactors are measured under similar conditions that differ marginally between DD and SD reactors. The formation of •OH and Ar metastable species is observed in optical emission spectra confirming the free radical-based water-splitting reactions for H2 generation. Interestingly, the use of high frequency leads to various frequency gaps within the 4–30 kHz range where there is neither the generation of filamentary discharge nor the H2 formation. These frequency gaps vary with GGs and the type of central electrode materials used in DBD reactors. In addition, an increase in the applied voltage controls the frequency gaps under study. H2 production of ∼3600 ppmv obtained with the Cu-containing SD reactor translates to over 21% water conversion.