Knowledge Bank

Infrared spectra of $O2$ and $CO2$ mixtures were studied in the laboratory between $1100cm-1$ and $1800cm-1$ for temperatures from 220 K to 296 K and total pressures up to 500 kPa using a Fourier-transform infrared spectrometer and a 2-meter-long, multiple-pathlength, White cell operating at 84 m. The intensity of the $O2$ continuum is strikingly enhanced by the addition of $CO2$. This result contrasts with our observations on the $CO2$ monomer and dimer lines, which show negligible enhancement upon the addition of $O2$. The shape of the $O2$ fundamental band sharpens with the addition of $CO2$, and at lower temperatures apparent P, Q, and R-branch features appear, which are attributed to a $CO2-O2$ complex. The observed $CO2$ enhancement of the $O2$ continuum absorption in the mid-infrared is consistent with our similar observations on the $1.27\mu m$ near-infrared, magnetic-dipole band of . Our observations agree with the theoretical calculations by Brown and Tipping in which they predicted significant enhancements by $H2O$ vapor of the continuum absorption of $N2$ and $O2$ for the vibrational fundamentals, attributed to the large electric dipole moment of $H2O$. We note that $CO2$, like $H2O$, has a large electrostatic moment, the electric quadrupole moment.