There are both physical and chemical interactions between amine-functionalized ionic liquids (ILs) and CO2. A method to estimate the ratio between physical and chemical interactions based on NMR spectra was proposed. Results showed that 21% of [aEMMIM][BF4] interacted with CO2 chemically at 1:1 (CO2/IL) stoichiometry, leading to a 94% contribution to the solubility, whereas 79% of [aEMMIM][BF4] interacted with CO2 physically at 0.017:1 stoichiometry, leading to a 6% contribution. This method can be extended to other similar systems. Tethering high sterically substitute group at IL helps to obtain an equimolar CO2 absorption. Crown Copyright (C) 2013 Published by Elsevier B.V. All rights reserved.