Knowledge Bank

Rotational spectra of $CnO(n=2,4,6$, and 8) have been observed by using a Fabry-Perot type Fourier-transform microwave (FTMW) spectrometer cooperated with a pulsed discharge nozzle (PDN). The molecules have been generated by a pulsed electric discharge of $C3O2$ diluted in Ar, and then adiabatically cooled to $\approx$ 2 K in a subsequent supersonic expansion. All the observed spectra of those species have been analyzed as linear molecules in the $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\sigma$-electronic ground state. The determined molecular constants, such as rotational, spin-spin coupling, and centrifugal distortion constants, have provided information on the C=C bond lengths, energy gaps between the excited $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}\Sigma +$ electronic state and the $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\Sigma -$ ground state, and rigidity of the molecules in respect of the bending vibrations.