Fragmentation ofC60: Experimental detection of C,C2,

Abstract

We report experimental evidence for the loss of neutral C2 from photoexcited C60 and C70. These species are detected by postionization with xuv radiation. Interestingly, C, C3, and C4 also are products in the nascent distribution. An upper limit to the translational energy release into C atoms has been obtained using a resonant autoionization transition. The detection of these products gives insight into the fragmentation mechanism of fullerenes and may also have an impact on the field of fullerene formation.PACS number(s): 36.40.+d, 82.30.Lp, 33.80.Eh There has been much experimental [1 -12] and theoretical work [13 -18] on the dissociation of C60 since its discovery in 1985 [19]. Most of the studies have focused on the detection of only even-numbered carbon clusters (C", n even) appearing in the mass spectra of fragmented C60 [1,14,16]. The original idea that these even numbers occur because of C2 loss by C60 has been taken as truth until recently [9,12,20]. Another possibility is that C60 may initially fragment via loss of a C atom to a metastable C59 followed by loss of another C atom to yield C58.We have used (2+ 1) multiphoton ionization to detect C atoms from C60 photodissociation previously, but were unable to determine if the C atoms resulted from the initial prompt dissociation of C60 (i.e. , in the fullerene stage, n )32) or from smaller fragments after total disintegration of the cage [20].We have also detected large neutral fragments (C5s -C32) from photodissociation of C60 using 118-nm (10.5 eV) radiation for single-photon ionization of the photoproducts [21]. In these measurements, the neutral fragment distribution matched the ionized fragment distribution. Unfortunately, the high ionization potentials for the small C"species [22] precluded their detection with this vacuuin ultraviolet light (for fragments smaller than about C6). We have recently installed an extremeultraviolet (xuv) light source on our mass spectrometer to photoionize all species with ionization potentials ( -14 eV, including all C fragments. In this paper, we report the first observation of C, C2, C3, and C4 in the nascent distribution of dissociated fullerenes and show that C2 loss is not the only small-fragment channel.The time-of-flight mass spectrometer (TOFMS) has been described in detail previously [20]. We utilize laser desorption for the generation of C60 or C70 vapor [7], followed by either 266 nm [from the saine Nd: YAG (yttri-'6 um aluminum garnet) laser that generates the xuv light] or 308-nm (XeCl excimer} laser light for dissociation. The dissociation products are then probed by an xuv laser. The xuv generating system consists of two Nd: YAG-pumped dye-laser systems, a frequency mixing cell, and a capillary waveguide for transport of the xuv beam [23] (see Fig. 1). One of the dye lasers is tuned to 557 nm and mixed with 354.7 nm from the frequencytripled Nd:YAG to generate 216.67 nm [using a 8-barium borate (BBO) crystal]. This uv beam is then combined on a dichroic mirror with the output of the second dye laser...

Tight-binding molecular dynamics simulations of radiation-induced fragmentation ofC60

“…This scenario is supported by some molecular dynamics simulations 10,11,35,36 and has been proven explicitly for photodissociation experiments using nanosecond laser pulses. 37,38 Experimentally, the detection of large neutral fragments from collision experiments, under conditions where the positively charged fragments show a bimodal distribution, was reported by McHale et al 39 A mass distribution closely mirroring that of the positively charged fragments was obtained and provided evidence in favor of a cleavage mechanism producing large neutral fragments at collision energies of 340 eV, rather than the dominance of successive C 2 emission.…”

Dissociation of singly and multiply charged fullerenes: Emission of C4, or sequential emission of C2?

“…4 Neutral C, C 2 , C 3 , and C 4 fragments have been identified, mostly by optical techniques. 9,[52][53][54][55] The importance of C 4 ejection cannot be established from these data, because neither their relative abundances nor their time dependence can be assessed. The odd-sized neutral fragments, for example, are not accompanied by any significant trace of C 59 ϩ or C 57 ϩ .…”

Direct Evidence for the Sequential DecayC60z+→C58zScheier1, Dünser2, Wörgötter3 et al. 1996Phys. Rev. Lett.650361View full textAdd to dashboardCite

“…Other authors, however, have claimed conclusive evidence against a successive statistical evaporation of C 2 [12,18,19]; they consider ejection of larger neutral fragments such as C 4 as the only essential reaction route [20]. As neutral fragments are rather difficult to identify [22] experimental evidence against or in favor of sequential C 2 emission has been so far only indirect. Concerning theoretical investigations it has been conjectured that even-sized fragments larger than C 2 are efficiently produced via an "unzipping" mechanism [23].…”