CO Rydberg series converging to the CO+ D and C states observed by VUV-fluorescence spectroscopy

The undispersed and dispersed vacuum ultraviolet fluorescence (lambda(F1) = 105-200 nm) after neutral photodissociation excitation of CO has been measured as a function of the exciting-photon energy in the region between 18.5 and 36 eV. The target-gas pressure dependence of the fluorescence intensities for energies below 23 eV was observed to be linear. For exciting photon energies above 23 eV photoelectron impact excitation of neutral CO from the ground to the CO(A (1) Pi) state causes a nonlinear pressure dependence of the undispersed fluorescence intensity. CO Rydberg states converging to the CO+ D and C states have been assigned on the basis of the recorded spectra. Previous assignments of the R-C(3s,4s,3p,4p) and R-D(3s,4s) Rydberg series could be supported and the identification of their vibrational levels have been considerably extended. Two new progressions (R-D(5s,6s)) have been assigned.