Abstract :
Two types of electric discharges were used: (a) In a supersonic expansion of pure CO gas. (b) In a U-shaped tube immersed in liquid nitrogen where either pure CO or mixtures of CO+He, CO+Ne, CO+NO are introduced.
In both cases, the analyzed emissions were exclusively those issuing from the negative glows of the discharges. Fourier Transform spectra were recorded in the 28 000–17 000 cm−1 visible spectral region and also in the 8000–2000 cm−1 infra-red interval.
Comparison of the two sets of spectra showed that spectra (a) correspond to excitation of the primary species whereas spectra (b) result from excitation of final compounds produced in the positive column. In the latter case, the main new observations are: (i) Selective excitation of particular upper state vibrational levels in the E3Σ−–a3Π Herman system. (ii) Appearance of the C1Σ+–B1Σ+ (0,0) Rydberg–Rydberg infrared band whereas the associated optical C1Σ+–A1Π Herzberg transition is absent. (iii) “Anomalous” vibrational distribution in the ground state vibration–rotation spectra.
All the above observations are concomitant with previously reported IR emissions involving very high rotational levels (up to J=120) in the ground state. To explain them, processes involving dissociative recombinations of dimer cations are suggested.
