RYDBERG SIMILAR-TO VALENCE PERTURBATIONS IN MATRIX-ISOLATED NO

The absorption spectrum of NO in rare gas matrices has been reinvestigated. The valence B2-PI(v',0) bands which, in the gas phase, show perturbations for v' greater-or-equal-to 7 due to homogeneous configuration mixing with the Rydberg C 2-PI state, appear unperturbed up to v' = 10 in Xe, 12 in Kr, 14 in Ar, and 19 in Ne matrices. The perturbations are shifted to higher energies due to the large blue matrix shifts experienced by the Rydberg states. They appear as irregular vibrational spacings, anomalous intensities, as well as modifications of the B2-PI(v',0) band profiles. The intensity patterns are qualitatively explained in terms of quantum-mechanical interference effects. When resonant with a multiphonon Rydberg band, Fano line shapes appear in place of the sharp B(v',0) valence lines. The line shapes have been simulated by means of the Fano theory assuming that only part of the Rydberg multiphonon quasicontinuum interferes with the sharp valence band. Good agreement is obtained with the experimental spectrum and the fitted Fano indices lie close to the calculated ones.