Absorption spectrum of C60 in the gas phase: Autoionization via core-excited Rydberg states

Abstract

The absolute absorption cross section of C 60 in the gas phase ͑830-870 K͒ was measured as a function of the photon energy ͑3.5-11.4 eV͒ ͑absorption spectrum͒. Absorption peaks at 7. 87, 8.12, 8.29, 9.2 eV and a dip at 8.45 eV observed are assigned as Feshbach resonances in the photoexcitation involving superexcited states. The superexcited states responsible for the 7.87, 8.12, and 9.2 eV peaks are assigned to be core-excited Rydberg states converging to the second, the third and the fourth ionization limits of C 60 ͑8.89, 9.12, 10.82-11.59 eV͒, respectively. The 8.29 eV peak is considered to originate from vibrational excitation of a totally symmetric pentagonal pinch mode of the superexcited state responsible for the 8.12 eV peak. Further, a relative photoionization quantum yield was estimated from the absorption cross section measured and the relative photoionization cross section reported. The yield increases particularly in the vicinity of 8 eV in accordance with a high efficiency of autoionization of the superexcited states. Ionization efficiency is not high in the vicinity of the first ionization energy, probably because of rapid energy dissipation into its vibrational modes. The spectrum below the ionization energy resemble the absorption spectra of C 60 in its solutions.

Absolute Total Photoionization Cross Section of C60in the Range of 25–120 eV: Revisited

“…The oscillator strength was calculated from this cross section curve, along with the absolute photoabsorption cross section curves at h ¼ 3:5 { 25 eV in the literature. [11][12][13] The oscillator strength for the h range from 3.5 to 40.8 eV is 178.5 and agrees well with that expected from the TKR sum rule and 60 times the total photoabsorption cross section of a carbon atom, 60 Â (C).…”

“…5. First, abs,A of Yasumatsu et al 11) was reevaluated using the vapor pressure at 850 K of Piacente et al, 20) or by dividing abs,A of ref. 11 by 4.…”

“…Actually, there exist only a few experimental works on the measurements of the absolute total photoionization cross section abs,I and absolute photoabsorption cross section abs,A of C 60 in the extreme UV region. 2,[11][12][13][14] In 1999, Berkowitz examined a abs,A spectrum of C 60 in the energy range of 3 -340 eV by compiling the experimental cross section data then available. 10) In 2000, Jaensch and Kamke 12,13) determined the abs,A curve at the photon energy range of synchrotron radiation from 10 to 26 eV by a photon attenuation method, using a gas chamber filled with C 60 vapor and applying the Lambert-Beer law (gas chamber technique).…”

Characteristics and dynamics of superexcited states of diatomic molecules: General theoretical procedure

“…Experimental studies of SESs are increasing nowadays not only for diatomic molecules but also for larger molecules such as C 60 . 3,4 Purely theoretical studies, however, are sort of stuck, unfortunately, even for diatomic molecules except for the case of H 2 5-12 in spite of the fact that the multichannel quantum defect theory ͑MQDT͒ can nicely deal with the infinite number of Rydberg states. 2,[13][14][15] This is mainly because there is no effective theoretical method to reliably estimate the important electronic parameters.…”

Confirmation of C60in the Reflection Nebula NGC 7023

“…We used PAHFIT (Smith et al 2007a) to find that the ratio of C 60 to PAH emission is 0.01-0.03 in NGC 7023 and NGC 2023. We then compare the amount of UV starlight per C atom absorbed by C 60 (Yasumatsu et al 1996;Yagi et al 2009). and PAHs (Li & Draine 2001).…”