Interference Effects in the Rydberg Spectra of Naphthalene and Benzene

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Abstract
We report new studies of (portions of) the Rydberg spectra of naphthalene and benzene. The anti‐resonances in the Rydberg spectrum of naphthalene are analyzed in terms of the theoretical line‐shape parameters A [Eq. (3)], q [Eq. (4)], and Γ [Eq. (6)]. The values of the parameters deduced, together with a simple physical argument, imply that the matrix element coupling the zero‐order Rydberg state φR and the isoenergetic inhomogeneously broadened background levels {ψi} is less than 1 cm−1. The available data do not permit an unambiguous determination of the nature of the background transitions, and hence of the coupling mechanism. Two limiting cases are considered, one requiring strict compliance with symmetry properties of the zero‐order states, and one disregarding said symmetry properties because of vibronic mixing prior to the interaction of φR and {ψi}. Both schemes can be made to fit the experimental data, and both have deficiencies. A possible intermediate scheme is suggested; it requires the background intensity to arise from at least two electronic transitions, possibly including σ−sgr;* and σ−π* excitations.