1. Conclusions  Most of the peaks from time of flight spectrum of EMImBF 4 ionic liquid have been assigned. Assignments are confirmed by ab intio activation energy calculations.  Important threshold and appearance energies of main fragments of EMImBF 4 were determined experimentally.  It was demonstrated that threshold energies show negligible dependence on temperature.  It was shown that intensities of BF 2 + and EMIM + fragments depend strongly on temperature. The intensities of the peaks increase if temperature is raised. The exact mechanism responsible for that is still unclear. References 1. P. Wasserscheid, T. Welton, Ionic liquids in synthesis, 2 nd edition, Vol1, WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim (2008). 2. J.M. Earle, J.M.S.S. Esperanca, M.A. Gilea, J.N. Canogia Lopes, L.P.N. Rebelo, J.W. Magee, K.R. Seddon, J.A. Widegren, Nature, 439, 831-834 (2006). 3. L. Siinor, C. Siimenson, V. Ivaništšev, K. Lust E. Lust, J. Electroanal. Chem., 668, 30 (2012). Motivation Ionic liquids (ILs) are organic salts which are in liquid state at room temperature. Nowadays ILs are in focus of many investigations due to extraordinary combination of their physico-chemical properties such as low volatility, good ionic conductivity, chemical and thermal stability, extended liquidus range, wide electrochemical window and unique solvating properties, which enables usage of low melting salts, for example, in electrochemical devices, separation sciences, tribology, analytical chemistry [1]. Studies of IL gas phase are relatively new and there is not a large number of them, because the realization that ILs could be vaporized came only in 2006 [2]. The vapor phase experiments are valuable, because typically ab initio calculations predicting the structure and interactions of ILs are made on isolated gas- phase systems. Therefore experimental spectra could help confirm ab initio studies and prove validity of theoretical models. Moreover, it is attractive to study isolated ion pairs to examine IL decomposition pathways like dissociation or ionization, since decomposition products must be considered in specific applications. The purity of IL is a top priority, because even small concentrations of impurities can have a large impact on ILs’ properties changing its viscosity, conductivity, decomposition temperature and electrochemical window. To the best of our knowledge this is the first reported fragmentation mass spectra of EMImBF 4 ionic liquid. Experiment Experiments were performed at an undulator beamline I3 of the MAX-III synchrotron radiation facility (Lund, Sweden). A MgF 2 /Al coated grating was used in the monochromator and the higher harmonics of the undulator radiation were blocked by a LiF crystal. The time of flight (TOF) and partial ion yield (PIY) spectra were recorded using a Wiley-McLaren type ion time-of-flight spectrometer with a 320 mm drift tube and a 77 mm diameter Hamamatsu microchannel plate detector. Ab initio DFT calculations were performed using Spartan 14 software with the hybrid B3LYP functional. Near threshold photodissociation study of EMImBF 4 vapor: mass spectroscopy approach M. Tarkanovskaja 1, I. Kuusik 1, J. Kruusmaa 2,V. Reedo 1, V. Kisand 1, E. Nõmmiste 1 1 Institute of Physics, University of Tartu, Tartu, Estonia 2 Institute of Chemistry, University of Tartu, Tartu, Estonia Acknowledgements Help and assistance of MAX-Lab personnel is gratefully acknowledged. Financial support by the Estonian Ministry of Education and Research (IUT2-25), Estonian Science Foundation (grants 8216, 8737 and 9281), Estonian Nanotechnology Competence Center (EU29996), ERDF projects ( “IRGLASS’’ 3.2.1101.12-0027, ‘‘TRIBOFILM’’ 3.2.1101.12-0028, TK114, “NanoCom “ 3.2.1101.12-0010,"Theory and applications of Mesosystems”, „High- technology Materials for Sustainable Development“ TK117), Graduate School “Functional Materials and Technologies” (European Social Fund project 1.2.0401.09-0079), Development Fund of University of Tartu, are gratefully acknowledged Fig 1. Non-background corrected time of flight spectrum of EMImBF 4 vapor excited at 20 eV. The liquid cell temperature was 190 o C. The most prominent peaks are located at m/z=82,110 which were assigned as MIM + fragment and intact cation EMIM + respectively (for other assignments see table on the right). Fig 4. TOFMS of EMImBF 4 vapor at 190 o C showing the appearance of EIM + fragment around 8.4 eV. Sample 1-ethyl-3-methylimidazolium tetraflouroborate with stated purity of ≥99.0% was purchased from Sigma-Aldrich and used as received. Before experiment it was kept at room temperature under vacuum (≈5×10 -7 mbar) overnight. Then IL was evaporated from a quartz crucible to the sample region. This particular IL has promising applications as possible electrolyte in the electrochemical double layer capacitors, because of its relatively high conductivity and wide range of ideal polarizability [3]. Partial ion yield spectra m/zAssignmentE app 40, 41, 42C 2 NH 2, C 2 NH 3, C 2 NH 4 >10.5 48, 49B 10 F 2, B 11 F 2 >10.5 54,55, 56C 3 NH 4, C 3 NH 5, C 3 NH 6 >10.5 68, 69imidazolium – IM (C 3 N 2 H 4, C 3 N 2 H 5 ) >10.5 81, 82, 83methyl-imidazolium – MIM (C 4 N 2 H 5, C 4 N 2 H 6, C 4 N 2 H 7 ) 7.9, 8.2, 7.8 95, 96ethyl-imidazolium – EIM (C 5 N 2 H 7, C 5 N 2 H 8 ) 7.5, 8.4 109, 110, 111, 112 1-ethyl-3-methylimidazolium – EMIM (C 6 N 2 H 9, C 6 N 2 H 10, C 6 N 2 H 11, C 6 N 2 H 12 ) 111 – 7.6 110 – 7.4 129, 1301-ethyl-3-methylimidazolium fluoride – EMIMF (C 6 N 2 H 10 F, C 6 N 2 H 11 F) 9.8 159EMIMBF 2 >10.5 Assignments of the fragments and their appearance energies Fig 3. Partial ion yield spectra of MIM + and EMIM + cations at three different temperatures. PIY measurements were performed at temperature range of 170-250 o C over the photon energy range of 7-10.5 eV with 0.1 eV step. The measurement time was 100 s/step. The linear fits were applied to the slopes to determine the thresholds (shown as E, E1, E2 in the figure). The threshold energies almost do not depend on temperature for all fragments, which is expected since they are mostly determined by electronic properties. The appearance energy (E app ) is the minimum photon energy necessary for production of a given fragment ion from photon absorbing molecule. E app were determined by analyzing the TOFMS spectra measured at different excitation energies (see fig.4 as an example). Time of flight mass spectra (TOFMS) of EMImBF 4 Fig 2. Non-background corrected time of flight mass spectra of EMImBF 4 vapor excited at 20 eV. The two spectra correspond to the liquid cell temperatures of 190 and 250 o C. The spectra have been normalized to the MIM peak intensity. It can be seen that intensities of BF 2 + and EMIM + fragments are very susceptible to temperature changes. However, the reason for such behaviour is unclear.