Both carbamation and bicarbonation are of prime importance in the absorption reactions of CO2 in an aqueous NH3 solution, as they are related to the CO2 working capacity, regeneration energy, and the critical problem of blocking the gas pathway for the CO2 capture process. Herein, the influence of reaction temperature on the CO2 and NH3 reaction in an aqueous solution is demonstrated by a principal component analysis (PCA) and a two dimensional correlation analysis (2D IR COS) obtained from FT-IR, dependent on the reaction time. In contrast to the reaction at 298 K, conversion of the dominant reaction from carbamation to bicarbonation and respective conformational changes were observed at 278 K by PCA and 2D IR COS. The PCA results elucidate that two major reactions following the dependence of reaction time were divided into two regions, I and II. The turnover point was subsequently tracked in these two regions, where precipitation of ammonium bicarbonate occurred due to the limitation of solubility at this turning point. The interrelation and sequential variation of conformations in regions I and II were investigated by synchronous and asynchronous 2D correlation analyses. The combination of PCA and 20 IR COS provides a powerful and useful analytic method to capture and monitor the dynamics of complex chemical reactions. (C) 2011 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.