Ion-induced fragmentation of imidazolium ionic liquids: TOF-SIMS study

An upgraded TOF-SIMS VG Ionex IX23LS was used to study the fragmentation patterns of a series of asymmetric imidazolium ionic liquids [Cnmim][Tf2N], where n = 2, 4, 6, and 8, under bombardment by Ga+ ions with energies of 10–20 keV. Analysis of positive and negative secondary ion mass spectra showed that fragmentation of cations and anion proceeds via both one- and two-bond cleavage of molecular backbone. In addition, formation of methylene adducts [Cnmim(CH2)x]+, where x = 1–3, and associates containing anion constituents [CnmimO]+ and [CnmimF]+ was revealed. Lengthening of alkyl chain was found to result in a stronger fragmentation of cations, while the extent of ion-induced fragmentation of anion decreased with an increase of the n-value and with a decrease in the projectile impact energy.