Ultraviolet Photoionization Efficiency of the Vaporized Ionic Liquid 1-Butyl-3-Methylimidazolium Tricyanomethanide: Direct Detection of the Intact Ion Pair (Post Print)

摘要

We present the first direct measurement of a neutral, intact ion pair photoionization efficiency (PIE) curve for a vaporized ionic liquid, 1- butyl-3-methylimidazolium tricyanomethanide, using tunable vacuum ultraviolet (VUV) photoionization time-of-flight mass spectrometry (PI-TOFMS). The ionization potential (IP) for the ion pair is experimentally determined to be 6.6 0.5 eV, which matches reasonably well with the adiabatic IP of 7.3 0.2 eV calculated at the M06/6-31+G(d,p) level of theory. The lifetime to dissociation of the cation radical complex formed upon ionization of the ion pair is highly dependent upon entropic contributions. Thermal gravimetric analyses (TGA) determined the enthalpy of vaporization to be Hvap(298 K) = 143.5 6.2 kJ/mol and that vaporization of BMIM+TCM as ion pairs is the dominant mechanism for mass loss under the experimental conditions for VUV PI-TOFMS (T = 433 K).