First analysis of the B1Σ+ (Ï =1) Rydberg state in the lesser-abundant 12C17O isotopologue on the basis of the 1-Ï â€³ progression of the à ngström band system

- Emission spectroscopy of the B1Σ+-A1Π system in the rare 12C17O isotopologue.
- Rotational analysis of the 1-1 and 1-5 bands.
- First constants and new parameters of potential curve for B and A states.
- Isotopic dependences of the B1Σ+ state of all natural CO isotopologues.
- Irregularities inside the Ångström system.

So far unobserved in the 12C17O isotopologue, the 1−υ″ progression of the Ångström (B1Σ+-A1Π) band system was recorded under high resolution in the 17,200-22,950 cm−1 spectral region as an emission spectrum using high-accuracy dispersive optical spectroscopy. The 12C17O molecules were formed and excited in two steps in a stainless steel hollow-cathode lamp with two anodes. The emission from the discharge was observed with a plane-grating spectrograph and recorded by a photomultiplier tube.In the studied region, the full rotational structure of the 1-1 and 1-5 bands of the B-A system was observed, in total 114 spectral emission lines up to J″=21. All those lines were precisely measured with an estimated accuracy of about 0.0030 cm−1, and rotationally analyzed. As a result, many molecular constants were determined for the B1Σ+ and A1Π states in the 12C17O isotopologue. In this paper we have also presented the results of calculations concerning RKR turning points, Franck-Condon factors, relative intensities, and r-centroids for the Ångström band system in the 12C17O molecule. We have also determined the value of the ΔG1/2 vibrational quantum, the isotope shifts, as well as the main, isotopically invariant parameters of the B1Σ+ Rydberg state in the CO molecule within the Born-Oppenheimer approximation.For the A1Π, υ=5 state, considerable irregularities of the rotational structure have been observed and analyzed in detail. Suspected candidates responsible for these perturbations have been identified. The B1Σ+, υ=1 state has been thoroughly analyzed in terms of possible perturbations and it emerged to be completely regular in the 12C17O molecule up to the observed maximum J value.