Far-Infrared Collision-Induced Absorption in CO2. II. Pressure Dependence in the Gas Phase and Absorption in the Liquid

Abstract

The pressure dependence of the collision‐induced spectrum in CO₂ at room temperature in the frequency region 7–250 cm⁻¹ is measured throughout this region as a function of density, ${\rho }_a$ , from 0–85 amagat. At each frequency the density variation of the absorption is fitted by ${\mathrm{\alpha (\nu ,\; \rho }}_a{\mathrm{)\hspace{0.17em}=\hspace{0.17em}\rho }}_a^2{\alpha }_2{\mathrm{(\nu )\hspace{0.17em}+\hspace{0.17em}\rho }}_a^3{\alpha }_3\mathrm{(\nu )}$ to obtain values of ${\alpha }_2\mathrm{(\nu )}$ and ${\alpha }_3\mathrm{(\nu )}$ . The coefficient ${\alpha }_2\mathrm{(\nu )}$ and its temperature dependence is discussed in the previous paper of this series. The coefficient ${\alpha }_3\mathrm{(\nu )}$ is negative in sign and has a band shape considerably sharper than that found for ${\alpha }_2\mathrm{(\nu )}$ . The Kramers–Kronig integral ${\pi }^{\text{−2}}{\mathrm{\int \alpha }}_3{\mathrm{(\nu )\nu }}^{\text{−2}}\mathrm{d\nu }$ is in reasonable agreement with the theoretical value of the third dielectric virial coefficient. Absorption in liquid CO₂ is measured at 0°C and compared with the band spectrum obtained in the gas phase at the same temperature. The peak intensity in the liquid spectrum occurs at a frequency 25 cm⁻¹ higher than in the gas phase. The integrated intensity ${\rho }_a^{\text{−2}}\mathrm{\int \alpha (\nu )d\nu }$ in the liquid is 3.2 ± 0.1 × 10⁻⁴ cm⁻²·amagat⁻², whereas that for the low density gas is 5.11 ± 0.20 × 10⁻³ cm⁻²·amagat⁻².