Vibrationally autoionizing Rydberg clusters: Spectroscopy and dynamics of pyrazine-Ar and -Xe clusters

Vibrational autoionization spectra of high Rydberg states of pyrazine-Ar an d -Xe van der Waals clusters were observed by two-color double resonance sp ectroscopy. Two Rydberg series converging to the same ionization threshold appeared in the spectra of both the clusters, while only one Rydberg series was seen in bare pyrazine. One of the series of the clusters was assigned to be of "gerade," which is the same Rydberg series as that found in bare p yrazine. The other series of the clusters was assigned to an "ungerade" ser ies, suggesting that the symmetry breakdown of the ion core is induced by t he cluster formation. For both the Rydberg series, apparently very small qu antum defects were involved, and the "gerade" and "ungerade" series were te ntatively assigned to the d (or s) and f Rydberg series, respectively. In c omparison with the bare molecule, the quantum defects of the clusters exhib ited slight shifts to the negative direction, indicating the decrease of th e binding energy of the Rydberg electron. The vibrational autoionization ef ficiency does not change upon the cluster formation, even above the dissoci ation threshold of the van der Waals bond. This fact indicates that the vib rational autoionization rate is much faster than the vibrational predissoci ation rate. (C) 2000 American Institute of Physics. [S0021-9606(00)00842-4] .