Equilibrium Measurements of the NH₃-CO₂-H₂O System: Speciation Based on Raman Spectroscopy and Multivariate Modeling

Table 2

Vibrational assignments of (NH₄)₂CO₃, NH₄HCO₃, and H₂NCOONH₄ aqueous solutions, and omitted frequencies in the respective PLS-R models. Adapted from the data of Wen and Brooker [10].

Frequency	Assignment	Omitted frequencies for the PLS-R anion model
		Carbonate	Bicarbonate	Carbamate
3390	Antisymmetric N-H stretch of NH3	X	X	X
3310	Symmetric N-H stretch of NH3	X	X	X
3220	Fermi resonance with N-H symmetry stretch of NH3	X	X	X
3050	Symmetric N-H stretch of	X	X	X
2850	A combination of fundamentals of	X	X	X
1690	NH2 deformation of	X	X	X
1645	Antisymmetric deformation of NH3			X
1630	C-O antisymmetric stretch of			X
1550	Antisymmetric CO2 stretch of			X
1436, 1380	CO antisymmetric stretch of	X, X	X, X	X, X
1430	Antisymmetric NH2 deformation of	X	X	X
1405	Symmetric CO2 stretch of	X	X	X
1360	CO symmetric stretch of	X		X
1302	C-OH bend of	X	X	X
1120	CN stretch of	X	X	X
1065	CO symmetric stretch of		X	X
1034	NH2 wag of	X	X
1017	C-OH stretch of	X	X	X
680	CO2 antisymmetric deformation of	X	X	X
640	(OH)-CO bend of	X	X	X
570	Torsion about CO2 skeleton of	X	X	X