The measurement of the infrared rotation-vibration spectrum of HCl(g) is a common experiment in the physical chemistry laboratory, which allows students the opportunity to explore quantization of rotational states in diatomic molecules. It is found that the CO2 vibration-rotation spectrum if used as an addition to the HCl experiment would give the students an opportunity to understand how the Pauli principle is properly interpreted in terms of the symmetry or antisymmetry of wavefunctions.