Modeling Carbon Dioxide Vibrational Frequencies in Ionic Liquids: IV. Temperature Dependence

CA Daly and C Allison and SA Corcelli, JOURNAL OF PHYSICAL CHEMISTRY B, 123, 3797-3803 (2019).

DOI: 10.1021/acs.jpcb.9b01863

In previous papers in the series, the vibrational spectroscopy of CO, in ionic liquids (ILs) was investigated at ambient conditions. Here, we extend these studies to understand the temperature dependence of the structure, dynamics, and thermodynamics of CO, in the 1-butyl-3-methylimidazolium hexafluorophosphate, bmimPF6, IL. Using spectroscopic mapping techniques, the infrared absorption spectrum of the CO, asymmetric stretch mode is simulated at a number of temperatures, and the results are found to be consistent with similar experimental studies. Structural correlation functions are used to reveal the thermodynamics of complete CO, solvent cage breakdown. The enthalpy and entropy of activation for solvent cage reorganization are found to be 6.9 and 7.6 (kcal/mol)/K, respectively, and these values are similar to the those for spectral, orientational, and translational diffusion. Caging times for CO, are calculated, and it is shown that the short time dynamics of CO, are unaffected by temperature, even though the long-time dynamics are highly sensitive to temperature.

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