Photo- versus pulsed field-ionization of individual high n (n≲57) Rydberg states: Resolved d,g series of benzene

Abstract

Low l Rydberg states of the polyatomic molecule benzene in the range 37≲n≲56 are resolved for the first time by double resonance excitation using narrow-band ultraviolet (UV)-laser pulses. The short lived Rydberg states are detected by photoexcitation of the ionic core with the same laser pulses followed by fast autoionization of the Rydberg states. The Rydberg spectrum obtained shows clear substructure of individual high n Rydberg peaks with components of quantum defects δl=0.00, 0.015, and 0.04. It is compared with a delayed pulsed field ionization spectrum with a delay of 8 μs. The bright low l core-penetrating zero order states cannot be observed in the delayed pulsed field ionization experiment for n<50 since there is no mixing with the long-lived Stark manifold of noncore-penetrating high l Rydberg states in the residual electric stray fields present in our apparatus which is necessary to lengthen the lifetime to survive the delay of 8 μs. Our results for the observed low l Rydberg states agree with previous results from Rydberg spectroscopy of low n Rydberg states in benzene. This is an important step towards observation of continuous Rydberg series from n=3 up to n=56. Above n=56 the different n,l Rydberg states are mixed in the electric stray fields into a single n Stark manifold.