Vibrationally resolved electronic absorption spectrum of 1,2-dihydrogenated[60]fullerene has been recorded in a 6 K neon matrix after mass-selected deposition of m/z = 722 cations produced from reaction of protonated methane and C60 in an ion source. One system has the origin band at 688.5 ± 0.1 nm and another commencing at 404.8 ± 0.1 nm. Theoretical computations were used to calculate the relative energies of three isomers of dihydrogenated[60]fullerene and time-dependent density functional theory predicted the vertical excitations to 50 electronic states

Filipkowski, Karol

Maier, John P.

Rice, Corey Allen

edoc

M3028 ECS Journal of Solid State Science and Technology, 6 (6) M3028-M3030 (2017)JSS FOCUS ISSUE ON NANOCARBONS—IN MEMORY OF SIR HARRY KROTOElectronic Spectrum of Dihydrogenated Buckminsterfullerene in a6 K Neon MatrixK. Filipkowski, C. A. Rice, and J. P. MaierzDepartment of Chemistry, University of Basel, 4056 Basel, SwitzerlandVibrationally resolved electronic absorption spectrum of 1,2-dihydrogenated[60]fullerene has been recorded in a 6 K neon matrixafter mass-selected deposition of m/z = 722 cations produced from reaction of protonated methane and C60 in an ion source. Onesystem has the origin band at 688.5 ± 0.1 nm and another commencing at 404.8 ± 0.1 nm. Theoretical computations were usedto calculate the relative energies of three isomers of dihydrogenated[60]fullerene and time-dependent density functional theorypredicted the vertical excitations to 50 electronic states.© The Author(s) 2017. Published by ECS. This is an open access article distributed under the terms of the Creative CommonsAttribution Non-Commercial No Derivatives 4.0 License (CC BY-NC-ND, http://creativecommons.org/licenses/by-nc-nd/4.0/),which permits non-commercial reuse, distribution, and reproduction in any medium, provided the original work is not changed in anyway and is properly cited. For permission for commercial reuse, please email: oa@electrochem.org. [DOI: 10.1149/2.0071706jss]All rights reserved.Manuscript submitted December 5, 2016; revised manuscript received January 4, 2017. Published January 14, 2017. This paper ispart of the JSS Focus Issue on Nanocarbons–In Memory of Sir Harry Kroto.Fullerenes are spherical or ellipsoidal structures of pure carbon,such as C60, C70, and C84. These molecular geometries are the smallercounterparts of extended carboneous nanotubes. C60 is the most stablefullerene and was first generated more than 30 years ago in the labora-tory by laser vaporization.1 It has also been suggested that fullerenesform around stars with carbon-rich atmospheres and hydrogen-poorstellar environments.2–5 Hydrogenated amorphous carbon grains inthe interstellar medium (ISM) may decompose from shock waves intopolycyclic aromatic hydrocarbons (PAHs) and fullerenic species;6PAHs may comprise ≈ 20 % of carbon-containing compounds inspace.7,8Buckminsterfullerene C60 was first detected in a young planetary9and reflection nebula.10 However, given the significant photon flux be-low the hydrogen Lyman α energy, neutral C60 present in the diffuseISM would be ionized, being predicted first by Kroto.11 Recently, ithas been shown that C+60 is the carrier of five astronomical absorp-tion features, known as diffuse interstellar bands (DIBs).12–15 It hasalso been suggested that C+60 may undergo ion-neutral reactions withatomic hydrogen,2 making C60Hn+ (n > 1) cations possible speciesin the ISM. These types of protonated species could also be candidatemolecules for the DIBs observed towards reddened stars. Another ion-neutral reaction that would produce C60 H+2 is C60 + H3+ → C60 H++ H2, and recombing with free electrons, the reaction C60H + H3+→ C60H2+ + H2 can proceed. Hydrogenated fullerenes, C60 Hn , couldbe created in the diffuse ISM over billions of years; however, this isdependent on the electron capture and ionization rates.UV/Vis spectra were measured before in the liquid-phase of C60Hnn = 2,4 to determine if the desired synthesis was completed. In thecondensed phase, two distinct absorptions are present for C60H2 at710 and 435 nm.16 In this contribution, a vibrationally well-resolvedelectronic spectrum of C60H2 was measured in a 6 K neon matrix andvertical excitation energies were calculated to assist an assignment.Mass-selective deposition of C60 H+2 was undertaken; however, elec-tron recombination occurred with cations in the crystalline neon andonly neutral C60H2 was observed.MethodsExperimental.—The setup for mass-selected matrix isolation ofions is described elsewhere.17 Buckminsterfullerene C60 vapor wasgenerated by heating the sample to ca. 650 K. Cations, predomi-nately C60Hn+ n> 1 were produced in a hot cathode discharge sourcefrom C60 diluted in gaseous methane. Ions were extracted and guidedzE-mail: j.p.maier@unibas.chthrough an electrostatic bender to a quadrupole mass selector (QMS).Ions of m/z = 722 passed through the QMS and were codepositedwith a mixture of neon and CH3Cl (20 000:1) onto a rhodium-coatedsapphire plate at 6 K. CH3Cl acts as an electron scavenger, creatingCl− by dissociative electron attachment and compensating the positivecharge. After a ≈ 150 μm thick matrix was produced, electronic ab-sorption spectra were measured in the 280−1100 nm range by passingbroadband radiation through crystalline neon, parallel to the matrixsubstrate. Light was wavelength-dispersed by a 0.3 m spectrographand detected with a CCD camera. A photobleaching procedure wasemployed to distinguish absorptions of cations from those of neu-trals. The neon matrix was irradiated with UV light from a mediumpressure mercury lamp. Electrons are detached from Cl− and neutral-ize positively charged species. Absorptions which decrease upon UVirradiation have a cationic origin, whereas those which increase inintensity are due to neutral molecules.Computational.—Equilibrium structures for different isomers ofC60H2 were calculated with density functional theory (DFT) usingB3LYP functional18.19 and cc-pVDZ basis set.20 Computations werecarried out with the Gaussian 09 program package.21 Vertical excita-tion energies of the species (all with C1 symmetry) were calculatedwith time dependent (TD-DFT) to compare experimental and theoret-ical values.Results and DiscussionThe electronic spectrum of 1,2- dihydrogenated[60]fullerene (1,2-C60H2) in a 6 K neon matrix is illustrated in Figures 1 and 2. Thereis one system that has absorptions around 690 nm and another onebeginning at 410 nm. The bands in the near-UV are from a numberof electronic transitions and state-to-state mixing makes for a difficultassignment.The first dipole-allowed electronic transition (Figure 1) has an ori-gin band maximum at 688.5 ± 0.1 nm (14 524 cm−1). There is asecond absorption in a 6 K neon matrix at 677.0 nm (14 771 cm−1),blueshifted to the origin band by 247 cm−1. This vibration is mostlikely a fullerenic breathing mode, involving the carbon cage-structureof the whole molecule. In the liquid-phase,16 the maximum is red-shifted relative to solid-neon by ca. 20 nm. This is due to solvent andtemperature effects, because the measurement was taken at 298 K.Upon photobleaching the matrix, the two bands at 688.5 and 677.0 nmgain intensity (Figure 1, red), concluding that the carrier is neutral.If these were to decrease in overall intensity, they would be from acationic species.) unless CC License in place (see abstract).  ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 131.152.105.233Downloaded on 2018-01-02 to IP ECS Journal of Solid State Science and Technology, 6 (6) M3028-M3030 (2017) M3029Figure 1. Electronic absorption spectrum of 1,2-dihydrogenated[60]fullerenein a 6 K neon matrix in the red of the visible region. The bottom trace was mea-sured after codeposition of m/z = 722 in neon and the top after photobleachingwith < 270 nm light.In the electronic absorption spectrum of 1,2-dihydrogenated[60]fullerene, the first apparent band system has an origin at404.8 nm. One of the most intense transitions is at 402.6 nm, be-ing 20 times stronger than the 404.8 nm one. The 398.3 nm band isdominant in this region and blueshifted to this is another transitionas intense as the one at 402.6 nm. These absorptions possess no sitestructure which is normally present in a crystalline neon matrix at6 K.22 It is difficult to make specific assignments of the electronicabsorption spectrum of C60H2 because of the density of electronicstates in the near-UV (Supplementary Information). Band maxima ofthe absorptions in the 405–350 nm region are collected in Table I.There are three possible isomers that could be produced in the ionsource: 1,2-, 1,4-, and 1,6- dihydrogenated[60]fullerenium (Figure 3).The most stable neutral has the hydrogens between two pentagonsalong a C=C hexagonal junction (1,2-C60H2). 1,4- and 1,6- C60H2 are32 and 83 kJ mol−1 , respectively, higher in energy relative to 1,2-C60H2 at the B3LYP/cc-pVDZ level. This can be explained simply bythe hydrogenation of unsaturated hydrocarbons. H2 addition to a C=Cbond is more favored than other pathways; this would be the mostprobable case for C60. Additionally, theoretical investigations haveFigure 2. Electronic absorption spectrum of 1,2-dihydrogenated[60]fullerenein a neon matrix at 6 K. The bottom trace was observed after deposition ofm/z = 722 into neon and the top after irradiation (< 270 nm) using a mediumpressure mercury lamp equipped with a water filter. Band maxima of labelsa–r are given in Table I.Table I. Band maxima in the electronic absorption spectrum of the1,2-dihydrogenated[60]fullerene, Figure 2.Label λ/nm ν˜/cm−1a 404.8 24704b 402.6 24839c 398.3 25107d 396.7 25208e 394.8 25329f 391.6 25536g 388.3 25753h 385.9 25913i 382.3 26157j 379.5 26350k 376.4 26567l 374.8 26681m 372.9 26817n 367.9 27181o 365.3 27375p 362.1 27617q 358.9 27863r 353.4 28297shown that 1,2-C60H2 is the lowest energy isomer on the potentialenergy surface.23,24The ground-state energies of 1,2-, 1,4-, and 1,6-C60H2 were calcu-lated in the C1 symmetry group. TD-DFT was used to predict the ver-tical excitations at the B3LYP/cc-pVDZ level (Supplementary Infor-mation). The first dipole-allowed electronic transition for 1,2-C60H2is located at 667 nm and is in good agreement with the experimentalvalue (688.5 nm). 1,4- and 1,6-C60H2 have their first excited elec-tronic state at 658 and 1058 nm; however, the oscillator strength ofthat for 1,4-C60H2 is 60 % weaker than of 1,2-C60H2. 1,6-C60H2 hasa similar f -value as 1,2-C60H2, but these wavelengths are not withinthe detection range of the matrix setup.TD-DFT predicts numerous excited electronic states for all threeconsidered isomers in the UV. Therefore, a definite assignment forthe UV absorptions would be inconclusive. There are approximatelya dozen (Supplementary Information) dipole-allowed electronic tran-sitions in the 420–350 nm region where the band system is observed(Figure 2).1,2-C60H2 is not a particularly stable molecule and deprotonationof hydrogenated fullerenes can be achieved with mild bases. The highacidity of the fullerenyl C−H bond arises from the fact that C60H2has pKa1 and pKa2 values of 4.7 and 16, respectively,25 allowing forfurther functionalization of fullerene anions. This could be a possiblemechanism known interstellar molecules to react with fullerenes. Thetimescales could compensate for low densities in the ISM, making theformation of substituted fullerene feasible.Figure 3. Numbering of the relevant carbon sites for C60 molecule in icosa-hedral symmetry.) unless CC License in place (see abstract).  ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 131.152.105.233Downloaded on 2018-01-02 to IP M3030 ECS Journal of Solid State Science and Technology, 6 (6) M3028-M3030 (2017)ConclusionsA vibrationally well-resolved electronic absorption spectrum of1,2-dihydrogenated[60]fullerene has been measured in a 6 K neonmatrix. Theory and experiments show that this molecule has elec-tronic transitions commencing at 700 nm, ca. 410 nm, and continueinto the ultraviolet. This could be an encouragement for gas-phasespectroscopic studies utilizing, for example, the resonant-enhancedmultiphoton ionization technique, which could then be compared di-rectly with absorptions in the interstellar medium.26,27 Laser ablationin the presence of methane or hydrogen molecule would be one pos-sibility to produce C60H2 in a pulsed-supersonic beam, and spectro-scopically, the different C60Hn molecules would have absorptions inspecific regions of the visible spectrum.References1. H. W. Kroto, J. R. Heath, S. C. O’Brien, R. F. Curl, and R. E. Smalley, Nature, 162,318 (1985).2. H. W. Kroto and M. Jura, A&A, 275, 263 (1992).3. A. Goeres and E. Sedlmayr, A&A, 216, 265 (1992).4. I. Cherchneff, Y. H. Le Teuff, P. M. Williams, and A. G. G. M. Tielens, A&A, 572,357 (2000).5. G. Pascoli and A. Polleux, A&A, 799, 359 (2000).6. A. Scott, W. W. Duley, and G. P. Pinho, ApJL, L193, 489 (1997).7. C. Joblin, A. Le´ger, and P. Martin, ApJ, L79, 393 (1992).8. A. G. G. M. Tielens, ARA&A, 289, 46 (2008).9. J. Cami, J. Bernard-Salas, E. Peeters, and S. E. Malek, Science, 1180, 329 (2010).10. K. Sellgren, M. W. Werner, J. G. Ingalls, J. D. T. Smith, T. M. Carleton, and C. Joblin,ApJL, L54, 722 (2010).11. H. W. Kroto, Chains and grains in interstellar space. In Polycyclic aromatic hydro-carbons and astrophysics, p. 197, Dordrecht, The Netherlands: D. Reidel PublishingCompany. 1987.12. E. K. Campbell, D. Gerlich, M. Holtz, and J. P. Maier, Nature, 322, 523(2015).13. G. A. H. Walker, D. A. Bohlender, J. P. Maier, and E. K. Campbell, ApJL, L8, 812(2015).14. E. K. Campbell, M. Holz, and J. P. Maier, ApJ, 17, 822 (2016).15. E. K. Campbell, M. Holz, and J. P. Maier, ApJL, L4, 826 (2016).16. R. V. Bensasson, E. Bienvenue, J.-M. Janot, S. Leach, P. Seta, D. I. Schuster,S. R. Wilson, and H. Zhao, Chem. Phys. Lett., 245, 566 (1995).17. P. Freivogel, J. Fulara, D. Lessen, D. Forney, and J. P. Maier, Chem. Phys. 335, 189(1994).18. A. D. Becke, J. Chem. Phys. 5648, 7 (1993).19. C. Lee, W. Yang, and R. G. Parr, Phys. Rev. B, 785, 37 (1988).20. T. H. Dunning, J. Chem. Phys. 1007, 90 (1989).21. Gaussian 09, Revision E.01, M. J. Frisch et al. Gaussian Inc. Wallingford CT.2009.22. K. Filipkowski, J. Fulara, and J. P. Maier, Int. J. Mass Spectrom. 354, 188 (2013).23. C. C. Henderson, M. C. Rohlfing, and P. A. Cahill, Chem. Phys. Lett. 383, 2131993.24. S. Narita, T. Morikawa, and T.-I. Shibya, J. Mol. Struct. 263, 528 (2000).25. M. E. Niyazymbetov, D. H. Evans, S. A. Lerke, P. A. Cahill, and C. C. Henderson,J. Phys. Chem. 13093, 98 (1994).26. L. M. Hobbs, D. G. York, T. P. Snow, T. Oka, J. A. Thorburn, M. Bishof,S. D. Friedman, B. J. McCall, B. Rachford, P. Sonnentrucker, and D. E. Welty, ApJ,1256, 680 (2008).27. L. M. Hobbs, D. G. York, J.A. Thorburn, T. P Snow, M. Bishof, S. D. Friedman,B. J. McCall, T. Oka, B. Rachford, P. Sonnentrucker, and D. E. Welty, ApJ, 32, 705(2009).) unless CC License in place (see abstract).  ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 131.152.105.233Downloaded on 2018-01-02 to IP 

Electronic Spectrum of Dihydrogenated Buckminsterfullerene in a 6 K Neon Matrix

K. Filipkowski

C. A. Rice

J. P. Maier

Crossref

ECS Journal of Solid State Science and Technology

http://edoc.unibas.ch/58299/1/20180102110716_5a4b59d4a0eb3.pdf

Electronic Spectrum of Dihydrogenated Buckminsterfullerene in a 6 K Neon Matrix

Abstract

Similar works

Full text

Available Versions

edoc

Crossref