Predissociation of Rydberg states of CO investigated by the detection of atomic fragments

Predissociation of Rydberg states of CO has been investigated by the C (P-3 and D-1) and O(P-3) photofragment measurements in the region of 103 000-11 4 000 cm(-1) (88-97 nm). The simulations of the rotational structures of np and nf Rydberg states were also carried out by using the l-uncoupling Hami ltonian model. The photofragment yield spectra were compared with the ion-d ip spectra which correspond to the absorption spectra, indicating that all the Rydberg states, ns, np, nd, and nf converging to the X (2)Sigma (+) CO ion, were subject to the predissociation. It was found that the lower memb er np pi and nd pi states exhibit two dissociation path ways, that is the C (P-3)+O(P-3) and the C(D-1)+O(P-3) channels. Especially, for the 4p pi L (1 )Pi (v=0) state the two channels were found to be competitive with respect to parity as well as rotational quantum number J. At higher np series, such a parity and J-dependence of the predissociation disappeared, and the obse rved rotational structure was simulated very well by the model with no pari ty nor J dependence. For the nd sigma states, the spectra of the 3d sigma a nd 5d sigma (v=0) states were diffuse, while the 4d sigma (v=0) state showe d a rotationally resolved photofragment yield spectrum. All the photofragme nt yield spectra of the nf(v=0) states exhibited sharp structures compared with those of other Rydberg states with a small l value. From a comparison between the photofragment yield spectrum and the ion-dip spectrum, it was f ound that the predissociation rate of the e-symmetry component is larger th an that of the f-symmetry component. It was suggested that the e-symmetry l evels predissociate through D-' (1)Sigma (+) valence states, while the f-sy mmetry levels predissociate through the 2 (1)Pi state. (C) 2001 American In stitute of Physics.