Absolute absorption cross sections of gas phase C60 at 600 °C

Brady, Brian B.; Beiting, Edward J.

doi:10.1063/1.462967

Cited by 33 publications

(25 citation statements)

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“…These peaks are also observed in the spectra of C 60 in n-hexane solution [22][23][24][25] and in Ar matrix. 26 The absolute absorption cross sections of C 60 in the gas phase has been reported in an ultraviolet-visible range, 27,28 and agree with the absorption cross sections measured in the present study. By consulting the peak assignments given in these studies, one concludes that the 3.8, 4.9, and 6.0 eV bands are assignable to electronic transitions from 1 A g ͑ground state͒ to 3 1 T 1u , 6 1 T 1u , and 8 1 T 1u states, respectively.…”

Section: Absorption Bands Below the Ionization Energysupporting

confidence: 88%

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

Yasumatsu

Kondow

Kitagawa

et al. 1996

The Journal of Chemical Physics

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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.

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Section: Absorption Bands Below the Ionization Energysupporting

confidence: 88%

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

Yasumatsu

Kondow

Kitagawa

et al. 1996

The Journal of Chemical Physics

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“…Based on Klots's model [11], nearly ten 4-5 eV photons are supposed to be absorbed by one free C60 or C70 molecule in order to arrive at a temperature of 3000-4000 K leading to thermionic emission [8,9]. However, it was reported [12] that C60 starts to decompose at 1300 K. Here, we report direct observation of a transition from delayed ionization to direct ionization in the multiphoton absorption, where the appearance threshold for direct ionization of C60 is found at 5.8 eV rather than at ionization potential IP =7.5 eV. Based on our new results, we may ask, "Does delayed ionization for free C60 and C70 really result from thermionic emission of electrons following multiphoton absorption?"…”

Section: Direct Observation Of Transition From Delayed Ionization To mentioning

confidence: 99%

Direct observation of transition from delayed ionization to direct ionization for freeC60andC70<

Zhang

Stuke

1993

Phys. Rev. Lett.

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Transition from direct ionization to delayed ionization for free C60 and C70 is observed below the ionization potential (IP =7.5 eV). It depends on the excitation wavelength as well as the pulse energy. The appearance threshold for direct ionization is found at -5.8 eV. These can hardly be explained by thermionic emission; therefore, we propose that triplet states at -1.7 eV (=7.5 -5.8 eV) should play an important role in the multiphoton ionization of free C60 and C70 and the intramolecular interaction of many triplet states gives rise to delayed ionization. To confirm our proposition, we have carried out further experiments using two laser ionization. PACS numbers: 36.40.+d, 33.80.Rv Delayed ionization is ionization that occurs after the excitation pulse is over. It has been found in atoms [1], molecules [2], molecular adducts [3], and clusters [4].Although different mechanisms were proposed for delayed ionization in different systems, interaction with long-lived electronic excitation was generally involved [1][2][3][4]. Since 1990, however, thermionic emission has replaced long-lived electronic excitation as the mechanism for clusters [5,6]. For free C60 and C70, decay tails due to delayed ionization were observed in multiphoton ionization and vanished in single-photon direct ionization [7,8]. It looked similar for different wavelengths in the 248 -532nm (5-2.3eV) range [8] but depended on pulse energies (fluences) [9], where the measured slope n > 4 could not be understood by simple multiphoton ionization; thermionic emission was therefore considered the mechanism again. Recently, we found delayed ionization to be absent in multiphoton ionization of free C60 and C70 using high intensity subpicosecond laser excitation at 248 nm [10]. As the mechanism for this, direct ionization through coherent two-photon absorption under very high intensity excitation may not directly question the general validity of thermionic emission. Based on Klots's model [11], nearly ten 4-5 eV photons are supposed to be absorbed by one free C60 or C70 molecule in order to arrive at a temperature of 3000-4000 K leading to thermionic emission [8,9]. However, it was reported [12] that C60 starts to decompose at 1300 K. Here, we report direct observation of a transition from delayed ionization to direct ionization in the multiphoton absorption, where the appearance threshold for direct ionization of C60 is found at 5.8 eV rather than at ionization potential IP =7.5 eV. Based on our new results, we may ask, "Does delayed ionization for free C60 and C70 really result from thermionic emission of electrons following multiphoton absorption?" Free C60 and C70 were generated by heating an oven (~500°C) containing pure C60/C70 powder [13] under a 5xlO~8 mbar vacuum. The oven was mounted -1 cm below an ionization area that was located between two ion optics electrodes of our linear time-of-flight mass spectrometer. The extraction voltage was held constant. The apparatus and measurements have been fully described previously [14]. Standard excimer las...

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“…The vibronic spectra of C 60 exhibit both allowed and symmetry-forbidden transitions. Extensive theoretical and experimental investigations enabled bands and lines in spectra of fullerene C 60 to be identified [9,[13][14][15][16][17][18][19][20][21][22][23][24][25][26] and general trends of the shift upon changing the nature of the medium to be explained [13,14]. As a rule, n-alkanes were used as the solvents [13,14].…”

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confidence: 99%

“…The bands and symmetry assignment of transitions for C 60 have been described in detail [16]. Measurements at low temperatures were made in glassy solvents such as toluene [15], 3-methylpentane, and hexane [16,17] at 77 K, in inert-gas matrices at 4.2 K and lower [9,18,19,26], and in the gas phase (in molecular beams cooled by expansion) [21][22][23][24]. Studies of vibronic spectra of polymers are sparse and are carried out mainly for C 60 absorption in polymethylmethacrylate (PMMA) [25,27] and polystyrene (PS) [28,29].…”

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Absorption and fluorescence spectra of C60 fullerene concentrated solutions in hexane and polystyrene at 77–300 K

Pavlovich

Shpilevsky

2010

J Appl Spectrosc

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The locations of the 0 0 0 -bands for S 1 ← S 0 and S 1 → S 0 transitions have been found for C 60 solutions in hexane. It is shown that the profile of the S 1 ← S 0 band is mainly shaped by h u (4), t 1u (4)-and h g (1), a g (2)-modes that are active in absorption. Bands involving the h u (4)-and t 1u (4)-modes in the emission process have also been identified in the fluorescence spectrum. The appearance of the 0 0 0 -band in the forbidden 1 1 T 1g ← 1 1 A g transition is explained by symmetry reduction in the C 60 +environment system due to the interaction of electrons with local phonons. The temperature coefficients of the red shift for the 256.3-and 328.3-nm bands of allowed 1 T 1u ← 1 1 A g transitions for C 60 in hexane are equal to -1.45 and -0.46 cm -1 ⋅K -1 , respectively. The peak and half-width values of the 337.2-nm band for C 60 in polystyrene remain unchanged on cooling to 77 K. Absorption in the 700-800-nm region for concentrated hexane solutions of fullerene at 292 K results from the production of (C 60 ) n -clusters.Keywords: vibronic spectra, broadening, temperature effect, dispersion interactions, 0-0 band, solvatochromic shift, (C60)n-clusters.Introduction. The spectral properties of fullerene C 60 are interesting because of the broad application of materials based on carbon nanoparticles in science, industry, and medicine [1][2][3][4][5][6][7]. The solution of several astrophysical problems was also directly related to the study of the spectral properties of fullerenes [8,9]. Polymers that can be used as a basis for creating optical emission limiters, photo-conducting materials, and materials suitable for transforming solar energy into electrical are being sought [3, 10-12]. For example, the ability of C 60 bound covalently to phthalocyanine to transform long-lived (0.2 ms) photoinduced states with charge separation [11] was used to fabricate a solar cell in which the polymer matrix acted as an external light-collecting antenna and effected charge transfer into the reaction center, the phthalocyanine-fullerene dyad [12].Fullerene C 60 is a spherical molecule with point-group symmetry I h . The unique structure is responsible for its unusual photophysical properties that differ substantially from those of heterocyclic compounds. The vibronic spectra of C 60 exhibit both allowed and symmetry-forbidden transitions. Extensive theoretical and experimental investigations enabled bands and lines in spectra of fullerene C 60 to be identified [9,[13][14][15][16][17][18][19][20][21][22][23][24][25][26] and general trends of the shift upon changing the nature of the medium to be explained [13,14]. As a rule, n-alkanes were used as the solvents [13,14]. The bands and symmetry assignment of transitions for C 60 have been described in detail [16]. Measurements at low temperatures were made in glassy solvents such as toluene [15], 3-methylpentane, and hexane [16,17] at 77 K, in inert-gas matrices at 4.2 K and lower [9,18,19,26], and in the gas phase (in molecular beams cooled by expansion) [21][22][23][24]....

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Absolute absorption cross sections of gas phase C60 at 600 °C

Abstract: Absolute partial and total crosssection functions for the electron impact ionization of C60 and C70Absolute photodissociation cross sections of gas phase sodium chloride at room temperature

Cited by 33 publications

References 8 publications

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

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

Direct observation of transition from delayed ionization to direct ionization for freeC60andC70<

Absorption and fluorescence spectra of C60 fullerene concentrated solutions in hexane and polystyrene at 77–300 K

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