Terahertz Optical Constants of Solid CO2

We report the optical constants of the solid CO2 (dry ice) measured using terahertz time domain spectroscopy. The CO2 ice sample was grown by vapor deposition method. The optical constants were obtained by minimizing the amplitude of the oscillations of refractive index in the spectral domain. We found that the mean refractive index of CO2 ice at 10 K is 1.485 between 0.2 and 1.6 THz with a standard deviation of 0.0137. The experiments were accompanied by first-principles density functional theory calculations using full-potential linear augmented plane wave method. The calculated refractive index is found to be 1.37 which is in reasonable agreement with the experimental value. In addition, the vibrational frequencies of solid CO2 were also studied using density functional perturbation theory, and the corresponding modes were assigned.