C₂₀ Carbon Clusters: Fullerene–Boat–Sheet Generation, Mass Selection, Photoelectron Characterization

Abstract

Electron-impact ionization in a time-of-flight mass spectrometer of C(20)H(0-3)Br(14-12) probes-secured from C(20)H(20) dodecahedrane by a "brute-force" bromination protocol-provided bromine-free C(20)H(0-2(3)) anions in amounts that allowed the clean mass-separation of the hydrogen-free C(20) (-) ions and the photoelectron (PE) spectroscopic characterization as C(20) fullerene (electron affinity (EA)=2.25+/-0.03 eV, vibrational progressions of 730+/-70). The extremely strained C(20) fullerene ions surfaced as kinetically rather stable entities (lifetime of at least the total flight time of 0.4 ms); they only very sluggishly expel a C(2) unit. The HOMO and LUMO are suggested to be almost degenerate (DeltaE=0.27 eV). The assignment as a fullerene was corroborated by the PE characterization of the C(20) bowl (EA=2.17+/-0.03 eV, vibrational progression of 2060+/-50 cm(-1)) analogously generated from C(20)H(10) corannulene (C(20)H(1-3)Br(9-8) samples) and comparably stable. Highly resolved low-temperature PE spectra of the known C(20) ring (EA=2.49+/-0.03 eV, vibrational progressions 2022+/-45 and 455+/-30 cm(-1)), obtained from graphite, display an admixture of, most probably, a bicyclic isomer (EA=3.40+/-0.03 eV, vibrational progression 455+/-30 cm(-1)). The C(20) (+(-)) and C(20)H(2) (+(-)) cluster ions generated from polybrominated perylene (C(20)H(0-2)Br(12-10)) have (most probably) retained the planar perylene-type skeleton (sheet, EA=2.47+/-0.03 eV, vibrational progressions of 2089+/-30 and 492+/-30 cm(-1) and EA=2.18+/-0.03 eV, vibrational progressions of 2105+/-30 and 468+/-30 cm(-1)).

Ab initio calculation of carbon clusters. II. Relative stabilities of fullerene and nonfullerene C24

“…Indeed, the bowl-shaped isomer of C 20 has been experimentally detected in photoelectron spectroscopy ͑PES͒ experiment. 8,13 The experiment provides a supporting evidence for the growth mechanism [32][33][34][35][36][37] of the so-called "pentagon road" 32 by which the formation of fullerenes from small carbon fragment can be realized via incorporation of pentagons through annealing ͑ജ1473 K͒, consistent with the IPR. This growth mechanism can explain the high yield of C 60 production.…”

“…It is also worthy to mention that a recent PES measurement 13 of C 20 fullerene has been reported. Here, we replot the simulated anion PES spectrum for C 20 fullerene ͓Fig.…”

“…The experimental photoelectron spectra of carbon clusters C n − in the size of n =2-29 and 44, 60, and 70 have been reported. 8,13,28,30,67,68 However, determination of the C n − structures based on the measured PES spectra is a challenging task especially for small-sized C n − clusters. This is largely …”

“…The IPR can explain the high stability of C 60 fullerene structure whose 12 pentagons are completely surrounded by hexagons, as well as predict successfully the stable fullerenes with "magic number" n = 32, 36, 50, 60, 70, 76, 78, and 84. [3][4][5][6][7][8][9][10][11][12][13] The IPR can be theoretically rationalized on both steric and -electronic grounds. Fullerenes with three-, four-, and seven-membered rings ͑3-, 4-, and 7-MRs͒ are reasonably ruled out due to extra local steric strain and loss of -delocalization.…”

“…21 There have been increasing research interests in small to medium-sized ͑n =20-36͒ carbon clusters since the discovery of the C 60 . [7][8][9][10][11][12][13]17,[22][23][24][25][26][27][28][29][30][31] In our previous paper ͑Paper I 26 ͒, we studied relative stabilities of various isomers of carbon cluster C 20 using high-level ab initio methods. In that study, the bowl-shaped "fullerene fragment" corannulene was theoretically identified as the ground-state isomer of C 20 , which has a lower energy than the ͑only͒ classical fullerene isomer of C 20 .…”