Microwave Absorption Spectrum of the CO+Ion

The $K=0\mathrm{}\to 1$ pure rotational spectrum of C${\mathrm{O}}^{+}$ ($X{}_{}{}^2{}_{}{}^{}\Sigma$, $v=0\mathrm{}$) has been detected in a direct absorption experiment, in which microwave radiation is passed through a $3\frac{1}{2}$-m-long dc glow discharge in carbon monoxide or a helium-carbon-monoxide mixture. The discharge tube is cooled with liquid nitrogen, and the signal is detected with source modulation and computer-controlled signal averaging. The measured frequencies are 117 692.55 MHz ($J=\frac{1}{2}\to \frac{1}{2}$) and 118 101.99 MHz ($J=\frac{1}{2}\to \frac{3}{2}$).