HELIUM NANODROPLET ISOLATION OF IONIC LIQUID VAPOR: INRARED LASER SPECTROSCOPY OF [EMIM][Tf$_2$N]

Author Institution: Department of Chemistry, University of Georgia, Athens, Georgia, USA 30602The Infrared spectrum of the vapor produced upon thermal vaporization of the [emim][Tf$_2$N] ionic liquid has been obtained using the helium nanodroplet isolation method. Despite the low vapor pressure of [emim][Tf$_2$N], sufficient gas phase densities are produced, allowing for efficient helium nanodroplet pick-up. The mass spectrum of the emim[Tf$_2$N] doped droplet beam shows signatures \textbf{2007}, \textit{9}, 982. Strasser, D.; Goulay, F.; Belau, L.; Kostko, O.; Koh, C.; Chambreau, S. D.; Vaghjiani, G. L.; Ahmed, M.; Leone, S. R. textit{Journal of Physical Chemistry A} \textbf{2010}, textit{114}, 879.} that have been attributed in gas phase measurements to the presence of isolated, intact [emim][Tf$_2$N] ion-pairs. Furthermore, the mass spectrometry results indicate that emim[Tf$_2$N] does not undergo thermal decomposition at 410 K. Comparisons are made between the experimental measurements and \textit{ab initio} calculations (mp2/6-311++g(d,p)) of the CH stretch vibrational bands and permanent electric dipole moments for several [emim][Tf$_2$N] low energy isomers. The helium nanodroplet infrared spectrum of this species provides rather definitive support to the previously suggested vaporization mechanism of ionic liquids. \textbf{2007}, \textit{111}, 3191. Chambreau, S. D.; Vaghjiani, G. L.; To, A.; Koh, C.; Strasser, D.; Kostko, O.; Leone, S. R. \textit{Journal of Physical Chemistry B} \textbf{2010}, 114, 1361. Maginn, E. J.; Kelkar, M. S. \textit{Journal of Physical Chemistry B} \textbf{2007}, \textit{111}, 9424.