Simultaneous ion-pair photodissociation and dissociative ionization of an ionic liquid: velocity map imaging of vacuum-ultraviolet-excited 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide

摘要

Isolated gas-phase ionic liquid (IL) molecules, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Emim+][Tf₂N−]), are excited by laser-produced high-harmonic extreme ultraviolet light in the 17−26 eV range and the ions are probed by velocity map imaging. The velocities of the intact cation, Emim+, and intact anion, Tf₂N−, are recorded in separate velocity map images. The kinetic energy distribution of the intact cation has both slow ions arising from previously reported dissociative ionization and fast ions from ion-pair dissociation of the neutral isolated ionic liquid (positive and negative ion pairs) where the branching ratio is approximately 0.18 ± 0.02:0.82 ± 0.02. The intact anion is also detected with a momentum that complements the higher velocity intact cation fragment, indicating that the process arises from two-body dissociation of the neutral ion-pair. Similar angular distributions for the anion and the higher velocity cation indicate that the electronic transition, which is above the ionization threshold and leads to ion-pair dissociation of the neutral, has a dipole moment perpendicular to the dissociating ion-pair bond. Observation of the ion-pair dissociation upon photoexcitation of the IL vapor not only reveals a previously unobserved photodissociation pathway for the ionic liquid, but it also provides direct evidence for the existence of the ion pairs in the isolated gas phase molecules.View full textDownload full textKeywordsionic liquid, photodissociation, velocity map ion imagingRelated var addthis_config = { ui_cobrand: "Taylor & Francis Online", services_compact: "citeulike,netvibes,twitter,technorati,delicious,linkedin,facebook,stumbleupon,digg,google,more", pubid: "ra-4dff56cd6bb1830b" }; Add to shortlist Link Permalink http://dx.doi.org/10.1080/00268976.2012.673019