Higher excited states of benzene: Symmetry assignments of six gerade Rydberg series by four-photon absorption spectroscopy

Abstract

We report the observation of six gerade Rydberg series in benzene converging to the first ionization potential, seen in the region from 14 500–18 500 cm−1 as four-photon resonances in the five-photon ionization spectrum of the jet-cooled molecule. Polarization ratios measured for each transition in two- as well as four-photon resonance aid in determining excited state symmetries. We assign a Rydberg series with a quantum defect of 0.76 to higher members of the 3s Rydberg state first seen by Johnson in the near UV two-photon resonant three-photon ionization spectrum of benzene. The observed quantum defect, polarization ratios, and correlation with synchrotron absorption data all strongly support this assignment. Another series, with a quantum defect of 0.24, exhibits a polarization ratio of 4.5±0.5 signifying pure rank four activity. This is the first report of a purely rank four transition in a molecule. We assign this as an excitation to a d2 orbital which when converging to the first ionization potential (the 2E1g cation) gives rise to B1g and B2g Rydberg transitions. Within the D6h point group, these symmetries are allowed only in a four-photon transition. The number of gerade Rydberg series observed as four-photon resonances exceeds those available from the s-(1) and d-(3) bound members of a hydrogenic basis set. The participation of g(l=4) orbitals is indicated as the lowest members of two of the Rydberg series are at the n=5 level.

Benchmarking Second Order Methods for the Calculation of Vertical Electronic Excitation Energies: Valence and Rydberg States in Polycyclic Aromatic Hydrocarbons

“…We use the CCSDR(3) results as reference, with which we compare the results of the second order methods, because CCSDR(3) was shown to reproduce almost quantitatively the results of CC3 calculations not only for small molecules ,, but also for benzene, naphthalene and other organic chromophores ,,,, with only a few but predictable exceptions. Experimental values − can be found for some of the states included in our study.…”

New benzene absorption cross sections in the VUV, relevance for Titan’s upper atmosphere

“…By the end of the 20th century, new experimental techniques and theoretical studies allowed to 170 further investigate the absorption in the UV and review old interpretations. Grubb et al (1985) performed four-photon absorption spectroscopy measurements. They reported several Rydberg series in the benzene spectrum converging to the first ionization energy.…”

“…The narrow bands in the region region 1600 -1350Å get weaker and closer to each other towards shorter wavelengths, and merge into an absorption continuum at the IE. The sharp bands in this region have been assigned to Rydberg series with their corresponding vibrations (see for example Price and Wood, 1935;Herzberg, 1966;Pantos et al, 1978;Grubb et al, 1985). Some of the series 430 converge to the first IE, others to the second IE at 11.45 eV (1083Å).…”

Generalized quantum mechanical two-Coulomb-center problem (Demkov problem)

“…where odd multipole moments associated with the parameter q 1 , and the even multipoles with q 2 . It is clear that only one term 2q 1 /r in (25) does not vanish as R → 0. This term is naturally chosen as the unperturbed potential while the perturbation will be the first term of the second sum −q 2 R/r 2 cosϑ.…”