COLLISION-INDUCED ABSORPTION IN THE FAR INFRARED REGION IN GASEOUS AND LIQUID $CO_{2}$.

Present address of A. Rosenberg: Tel-Aviv University, Institute of Chemistry, Tel-Aviv, Israel.Author Institution: Science Center, North American Rockwell Corp., Thousand Oaks; Tel-Aviv University, Institute of ChemistryThe collision-induced spectrum of $CO_{2}$ has been investigated in the liquid phase and in the gas phase over a wide pressure range at various temperatures. The measurements were made with an f/3.8 grating spectrometer in the frequency region from $7 cm^{-1}$ to $300 cm^{-1}$. A pressure dependence study in the gas phase showed that the absorption, $\alpha(\nu)$ in $cm^{-1}$, can be expressed in the form, $\alpha(\nu) = A(\nu)\rho^{2} - B(\nu)\rho^{3}$, where $\rho$ is the density, $\nu$ is the frequency, and $A(\nu)\rho^{2}$ and $B(\nu)\rho^{3}$ are, respectively, the absorption corresponding to two and three body interactions. We were able to determine the absorption bands corresponding to $A(\nu)$ and $B(\nu)$ and find that the latter is considerably sharper than the former. The quadrupole moment, Q, of $CO_{2}$ was evaluated from both the integrated intensity, $\int A(\nu)d \nu$, and the Kramers-Kronig integral, $\int A(\nu)\nu^{-2}d\nu$, of the absorption band. The value of Q obtained by these two methods and those obtained by independent methods are all in good agreement. Using the value of Q determined from the $A(\nu)$-band, we find that $B(\nu)\nu^{-2}d\nu$ is in good agreement with the value given by the theory of the third dielectric virial coefficient. The absorption spectrum in liquid $CO_{2}$ shows essentially the same general shape as that in the gas except that the frequency at maximum absorption is shifted towards higher frequency by about 20\%. The possible significance of this result will be discussed