Fragmentação iônica por impacto de elétrons do 1-Butanol

Abstract

In this work, experimental measurements of the cations produced by electron impact ionization to the primary isomers of butanol were carried out using a Hiden Quadrupole Mass Spectrometer (EPIC 300), equipped with an RF head capable of measuring masses up to 300 amu (EPIC 300 ), with a resolution of 1 amu. This apparatus has an ionization stage and therefore can be operated in a residual gas analysis (RGA) mode, which was used in this investigation. The mass spectrum recorded for incident electronic energy of 70 eV, normalized and placed on an absolute scale, revealed the relative probability of forming 76 different cations by direct ionization or dissociative ionization of 1-butanol. The relative abundances of the cations formed in this study compare reasonably well with the corresponding values reported in the literature. Individual partial ionization cross sections (PICS) for the 38 major cationic fragments observed, measured in the region of electron energies of 10 - 100 eV, were also obtained for the first time in this work. Total Ionization Cross Sections (TICS) were generated by the addition of the PICSs from the 38 cationic fragments of 1- butanol, which represent 96.6% of the measured cations in the mass spectrum. Our experimental data were compared with experimental data from Hudson et al. and theoretical data obtained by the BEB method, calculated at the OVGF approach levels. A good agreement between the TICSs measured and the results of the literature was found. In addition, the appearance energies (AEs) and Wannier exponents were determined for 36 of the 38 major cationic fragments observed in our experiments, most of them for the first time. We found a good agreement of our AEs with the data available in the literature. Absolute PICSs of the primary alcohols from C1 to C4 were compared for the incident electronic energy of 70 eV. Some differences in the CS of the cations were found, providing more knowledge about the fragmentation process in this energy. This study contributed with new experimental data needed to better understand the ignition process in order to provide efficient use of 1-butanol as a fuel.