Kinetics of dissociation and thermionic emission in the C60 and C70 molecules

Sandler, P.; Lifshitz, Chava; Klots, Cornelius E.

doi:10.1016/0009-2614(92)80073-k

Cited by 99 publications

(22 citation statements)

References 28 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…For the reaction just mentioned, for example, a value of 0.46 ± 0.16 eV is obtained [29]. This value agrees, within the error bar, with values reported for metastable dissociation of C z+ 60 (z = 1, 2) into C z+ 58 [30,31], and for electron induced dissociative post-ionization of C + 60 into C 2+ 58 [4]. However, the small differences which one would expect to see in the KER for different precursors (charge state z) and for different reactions and time windows (metastable versus induced) are still masked by the experimental uncertainties.…”

Section: B Appearance and Ionization Energies Of Multiply Charged C 70supporting

confidence: 72%

Electron impact ionization and dissociation of neutral and charged fullerenes

Matt

Echt

Rauth

et al. 1997

Z Phys D - Atoms, Molecules and Clusters

View full text Add to dashboard Cite

Three different types of electron impact ionization experiments have been performed, involving neutral and charged C 60 and C 70 . 1) We have determined absolute partial ionization cross sections for formation of parent ions C z+ 60 and C z+ 70 in charge states up to z = 4, and of singly and multiply charged fragments of size n ≥ 44 and n ≥ 50 from C 60 and C 70 neutral precursors, respectively. 2) Previous appearance energy measurements of C 70 have been improved and extended to z = 5; ionization energies are found to depend linearly on the charge state of the precursor, in agreement with theoretical predictions. 3) A beam of mass selected C 2+ 60 has been crossed with an intense electron beam; the induced reactions (fragmentation, post-ionization, and dissociative post-ionization) have been analyzed.

show abstract

Section: B Appearance and Ionization Energies Of Multiply Charged C 70supporting

confidence: 72%

Electron impact ionization and dissociation of neutral and charged fullerenes

Matt

Echt

Rauth

et al. 1997

Z Phys D - Atoms, Molecules and Clusters

View full text Add to dashboard Cite

show abstract

“…This "linkedchains" stage may allow the ejection of fragments other than C2 and the subsequent annealing of the chain back into a fullerene before further destruction. These endings may have some impact on the discrepancy [15,33] between the theoretical numbers for C6o dissociation energetics (-10 -12 eV for Cz loss) [15,34] and the experimental numbers ( -5 -7 eV) [2,3,7,8,33]. Basically, the theoretical results are for loss of C2 from a closed, fullerenelike structure, whereas experiments probe loss of C-containing species (C -C4) from the different, moreopen structures discussed above.…”

Section: Shown Inmentioning

confidence: 99%

Fragmentation ofC60: Experimental detection of C,C2,
Lykke
¹

1995
Phys. Rev. A
40
1
14
0
View full text Add to dashboard Cite

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...

show abstract

“…Our result immediately shows that the yield of dimer emission, η C2 , does not exceed that of electron emission by more than a factor of η C2 /η e < (1 − η e )/η e ≈ 40 (or a maximum of 65 if we take into account the uncertainty of η e ). This constitutes the first experimental proof that thermionic emission is not merely parasitic to dissociation [6].…”

Section: Quantum Yield For Thermionic Emissionmentioning

confidence: 96%

“…This would support the notion that emission of C 4 or even larger fragments is a significant feeding channel in the amazingly efficient production of even-sized fragment ions below C + 58 . Is it really true that thermionic emission from excited C 60 is merely parasitic to emission of C 2 [6]? This would imply that the activation energy, D 60 , for the reaction C 60 → C 58 +C 2 is small compared to the ionization energy of C 60 , which is known to be IE 60 = 7.6 eV [14,15].…”

Section: Introductionmentioning

confidence: 98%

“…Excited fullerenes exhibit a rich spectrum of unimolecular decay modes: loss of C 2 or larger fragments [1][2][3][4], of electrons [5][6][7][8][9], and emission of photons (infrared and blackbody-like radiation) [10][11][12][13]. Each of these processes has been thoroughly investigated by a number of groups, none of them is quantitatively understood.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Photoexcited C60: fragmentation and delayed ionization

Deng

Littlefield

Echt

1997

Z Phys D - Atoms, Molecules and Clusters

View full text Add to dashboard Cite

We investigate two reaction channels of C 60 , excited by a pulsed laser at 355 nm: i) The relative and absolute yields of even-sized fragment ions are measured over a wide range of laser fluences. At low fluence we find a dramatic dependence of the abundance ratio of C + n−2 versus C + n . This result argues against the notion that unimolecular emission of C 4 or larger fragments contributes significantly to the production of even-sized fragment ions. ii) We count the number of delayed electrons emitted from C 60 , or one of its products, after photo-excitation. For high laser fluences, this number reaches a value of (2.6 ± 1.1) % per photoexcited C 60 . This sets a lower bound to the ratio of effective rate constants, k e (E * )/ k j (E * ), where k e refers to electron emission, and the sum in the denominator extends over all reaction channels.

show abstract

Kinetics of dissociation and thermionic emission in the C60 and C70 molecules

Cited by 99 publications

References 28 publications

Electron impact ionization and dissociation of neutral and charged fullerenes

Electron impact ionization and dissociation of neutral and charged fullerenes

Fragmentation ofC60: Experimental detection of C,C2,
Lykke
¹

1995
Phys. Rev. A
40
1
14
0
View full text Add to dashboard Cite

Photoexcited C60: fragmentation and delayed ionization

Contact Info

Product

Resources

About

Kinetics of dissociation and thermionic emission in the C60 and C70 molecules

Cited by 99 publications

References 28 publications

Electron impact ionization and dissociation of neutral and charged fullerenes

Electron impact ionization and dissociation of neutral and charged fullerenes

Fragmentation ofC60: Experimental detection of C,C2,Lykke1 1995Phys. Rev. A401140View full textAdd to dashboardCite

Photoexcited C60: fragmentation and delayed ionization

Contact Info

Product

Resources

About

Fragmentation ofC60: Experimental detection of C,C2,
Lykke
¹

1995
Phys. Rev. A
40
1
14
0
View full text Add to dashboard Cite