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

• Positive and negative TOF-SIMS spectra by 10–20 keV Ga+ bombardment of [Cnmim][Tf2N], where n = 2, 4, 6, 8, were measured.
• The predominant peaks were intact cation [Cnmim]+ and anion fragment F−.
• The sum intensity of positive cation fragments increased with an increase in the alkyl chain length (n-value).
• Ion-induced fragmentation of anion decreased with an increase of the n-value and with a decrease in the projectile energy.

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.

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