Absorption Spectrum ofN2in the Extreme Ultraviolet

Abstract

The absorption spectrum of ${\mathrm{N}}_2$ that corresponds to excited states in the range 12.2 - 17.0 ev has been investigated at large dispersion. Data are presented for a very extensive Rydberg series of bands, which are interpreted and correlated with previous observations. The ionization potential of ${\mathrm{N}}_2$ corresponding to the series limit is 15.577 volts. Absorption beyond this point is complete for a path of ∼0.5 mm atmos. From $\lambda 995$ to $\lambda 815$ the spectrum is well developed at ∼0.2 mm atmos. Here most of the absorption is due to bands that show an open rotational structure which could usually be analyzed to give values of $B^{\prime }-B^{\prime \prime }$. Several such bands above $\lambda 920$ are correlated with the known states $b$ and $b^{\prime }$. In general the internuclear distance, ${r_e}^{\prime }$, was found to increase with energy, up to values 40 percent larger than for the normal state. Vibrational constants are unexpectedly small ($\frac{{\omega }^{\prime }}{{\omega }^{\prime \prime }}<\frac{1}{3}$), and the ratio $\frac{{\omega }^{\prime }}{B^{\prime }}$ is about half the nearly constant value (Birge-Mecke rule) found for all the lower states of ${\mathrm{N}}_2$. There is some evidence that the coupling in a few of the more excited states represents a transition toward Hund's case $d^{\prime }$.