Determination of active sites for H atom rearrangement in dissociative ionization of ethanol

In an electron impact dissociative ionization experiment on C(2)H(5)OH, the formation of molecular ions requiring rearrangement of H atoms has been studied using a momentum spectrometer. H(3) (+), H(2) (+), HOH(+), and H(2)OH(+) observed in the experiment are molecular ions of this type. By comparing the mass spectrum of C(2)H(5)OH with that of its isotopomer C(2)H(5)OD, we determine the proportions of H-bond rearrangements involving carbon and oxygen sites. We find that the formation of H(3) (+) due to the breaking of the O-H bond and rearrangement of the H atoms on the CH(2) site is about 2.5 times as likely as its formation involving atoms from the CH(3) site alone. No such difference is seen in case of the H(2) (+) ion. The role of the O-H bond in formation of all observed ions has been assessed. Kinetic energy distributions of the molecular ions suggest that two or three electronically excited states contribute to their formation.