Ionização induzida por impacto de elétrons e fragmentação iônica dos álcoois primários metanol, etanol, 1-propanol e 1- butanol

Abstract

Experimental measurements of the cations created in the ionization and in the ionic fragmentation processes by electron impact were carried out in this work for the primary alcohols methanol, ethanol, 1-propanol and 1-butanol (C1-C4), using a HIDEN quadrupole mass spectrometer (EPIC 300), with a mass resolution of 1 um. The mass spectra (MS) of these alcohols for the electron impact energy of 70 eV and also, their total (TICS) and partial (PICS) ionization cross sections in the impact range of 10 to 100 eV were recorded. These results revealed the probability of formation of different cations formed in the electron collision with C1-C4 alcohols, by direct or dissociative ionization. Individual partial ionization cross sections (PICS's) were measured for 9 cationic methanol fragments, 20 cationic ethanol fragments, 31 cationic 1-propanol fragments and 38 cationic 1-butanol fragments. The TICS experimental data showed good agreement with results from the literature when available, and with theoretical data produced by the BEB and IAM-SCAR frameworks, while all the PICS produced in this work are new and were reported for the first time in the literature, with the exception of methanol. The curves of the thresholds formation of the parent ion and of the ionic fragments observed in the mass spectra with greater abundance were also registered, and their appearance energies (AE) were determined through the application of the Wannier theory extended to PICS. Through the values of the AE’s and the profiles of the PICS obtained, we propose for the first time some mechanisms of ionic fragmentation of the studied alcohols.