Mass spectrometric study of the negative and positive secondary ions emitted from ethanol microdroplets by MeV-energy heavy ion impact

We have investigated the negative and positive secondary ions emitted from ethanol droplets by 4.0-MeV C3+ impact to reveal the characteristic features of the reaction processes induced by fast heavy ions at the liquid ethanol surface. Analysis of the secondary ions was performed by time-of-flight mass spectrometry for microdroplet targets in a high vacuum environment. Fragment ions, deprotonated cluster ions, and trace amounts of the reaction product ions are observed in the negative secondary ions. The main fragment anions are C2HmO− (m = 1, 3, and 5) and C2H− generated by loss of hydrogen and oxygen atoms. The reaction product anions include deprotonated glycols, larger alcohols, and their dehydrated and dehydrogenated forms generated by secondary reactions between fragments and radicals. Furthermore, C3Hm− (m = 0-2) and C4Hm− (m = 0 and 1) are observed, which could be produced through a plasma state generated in the heavy ion track. Deprotonated ethanol cluster ions, [(EtOH)n − H]−, are observed up to about n = 25. [(EtOH)n − H]− have smaller kinetic energies than the protonated cluster ions (EtOH)nH+. This probably represents the effect of the positive Coulomb potential transiently formed in the ion track. We also discuss the size distributions and structures of the water- and CH2OH-radical-attached ethanol cluster ions.