ROTATIONAL STRUCTURE AND DISSOCIATION OF THE RYDBERG STATES OF CO INVESTIGATED BY ION-DIP SPECTROSCOPY

In a series of spectroscopic work of the Rydberg states of CO, we pres ent the rotational analysis of the v = 0 and 1 levels of the singlet n s, np, nd and nf-Rydberg states (n = 4-7). The spectra were measured b y ion-dip spectroscopy with triple resonance excitation via the 3s sig ma:B (1) Sigma(+) or the 3p sigma:C (1) Sigma(+) state. All the spectr a were rotationally well resolved and the term value, quantum defect a nd the rotational constant were obtained for each state. Through the a nalysis of the rotational structure, the coupling between the Rydberg electron and the ion core has been investigated. For the np-Rydberg st ates, a switching from Hund's case (b) to (d) was clearly observed wit h the increase of n. A significant perturbation was observed in the 6p pi (II)-I-1 and 7p pi (II)-I-1 states and it is suggested that these states are perturbed by the state with the same symmetry. For the nf-R ydberg states, the observed electronic energy was well analyzed by the long range force model and the precise ionization potential was obtai ned. The Rydberg<->valence and inter-Rydberg states interactions were also investigated. For the ns-Rydberg states, the interaction matrix e lement with the repulsive state was estimated from the measurement of linewidth of the rotational levels. The potential curve of the repulsi ve state to which ns-Rydberg states predissociate was also determined. Selective predissociation was found for the e-symmetry levels both in the v = 0 and 1 levels of the nf-Rydberg state. A strong interaction between the v = 0 levels of the 6d- and 7s-Rydberg states was observed . (C) 1995 American Institute of Physics.