Pressure-Induced Microwave Absorption in N2

Abstract

Pressure‐induced absorption in nitrogen has been studied at a frequency of 9260 MHz over the temperature range 238°–495°K and to pressures as high as 135 atm. Expressing the dielectric loss $\mathrm{\epsilon ″}$ in the form, ${\mathrm{\epsilon ″\hspace{0.17em}/\hspace{0.17em}\nu ̄\hspace{0.17em}=\hspace{0.17em}A\rho }}^2$ where $\mathrm{\nu ̄}$ is the frequency in cm⁻¹, and $\rho$ is the density, we find ${\text{A\hspace{0.17em}=\hspace{0.17em}1.7(1)\hspace{0.17em}×\hspace{0.17em}10}}^{\text{−10}}{\text{(T\hspace{0.17em}/\hspace{0.17em}273)}}^{\text{−2.5(2)}}{\mathrm{cm\; amagat}}^{\text{−2}}$ . The absorption coefficient $\alpha$ , in cm⁻¹ is then ${\text{α\hspace{0.17em}=\hspace{0.17em}1.07(6)\hspace{0.17em}×\hspace{0.17em}10}}^{\text{−9}}{\text{(T\hspace{0.17em}/\hspace{0.17em}273)}}^{\text{−2.5(2)}}{\mathrm{\nu ̄}}^2{\rho }^2$ . The molecular quadrupole moment for N₂, calculated via the Kramers–Kronig integral, using the result of the present investigation as the low‐frequency limit of ${\mathrm{\alpha (\nu ̄)\hspace{0.17em}/\hspace{0.17em}\nu ̄}}^2$ and the far‐infrared result of Bosomworth and Gush for N₂ at 300°K, is then 1.5 × 10⁻²⁶ esu.