Chemical absorption using aqueous amine-based solutions is the leading method for large-scale CO2 capture in industrial plants. This technology, however, still faces many challenges, in particular the high-energy requirements for solvent regeneration, which limit the economic viability of the technology. To guide the development of more energy-efficient amine solvents, this work studied the effect of molecular characteristics of diamines, including carbon chain length and type of amino functional group, on CO2 absorption and desorption performances. Six linear terminal diamines [NH2CH2C2-R, where R = NH2, NHCH3, N(CH3)(2), CH2NH2, CH2NHCH3, and CH2N(NH3)(2)] were investigated, and two monoamines, monoethanolamine (NH2CH2CH2OH, MEA) and 3-aminopropanol (NH2CH2CH2CH2OH, 3AP), were also tested as benchmarks. The CO2 absorption capacity in each amine was measured at 40 degrees C under atmospheric pressure using different CO2 gas partial pressures. C-13 and H-1 nuclear magnetic resonance spectroscopies were used to identify and quantify species present in the CO2-amineH(2)O system. Computational modeling was also carried out using Gaussian software to explain the effect of the chain length change on the stability of monocarbamate. The experimental results showed that the chain length extension from C-2 to C-3 led to a higher CO2 absorption capacity and more bicarbonate formation during the CO2 absorption process, and the computational study results supported this conclusion. In addition, the experimental results also demonstrated that increasing the substitution on one N atom in the tested diamines is favorable for a higher CO2 absorption capacity and more bicarbonate formation under a CO2 partial pressure of 101 kPa. Both chain length extension from C-2 to C-3 and an increase in the number of substituents on one N atom yield better performance in the CO2 desorption with regard to the CO2 higher cyclic capacity and faster initial CO2 release rate for the tested amines.