R. F. Tuktarov

RESONANT ELECTRON CAPTURE MASS SPECTRA OF FULLERENES C60 AND C70

Resonant electron capture by C60 and C70 was studied and it was established that long-lived (i.e. mass spectrometrically observable) parent negative ions are formed within an extremely broad energy region (0–14 eV). It has been shown that effective yield curves of C60− and C70− in the thermal energy region have resonant peaks at 0.05 ± 0.01 and 0.06 ± 0.01 eV, respectively. Owing to the higher energy resolution than in previously published experiments, it was possible to observe another resonant state at ca. 0 eV for both fullerenes (as a shoulder on the effective yield curve). This gives evidence of the possibility of s-electron attachment by the fullerenes. A correlation between electron capture, electron loss energy and photoelectron spectra was found. At 6.5 eV and above, C60− and C70− are subject to electron autodetachment and mean lifetime and mean decay rates were directly measured.

p-type doping in organic light emitting diodes based on fluorinated C60

We report on hybrid organic light emitting diodes based on spin coated PVK (poly(vinylcarbazole))/poly-TPD (poly(triphenyldiamine)) formulation electron blocking and conjugated peptide emitter layers while the hole blocking, BCP (2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline), layer is vacuum sublimed. The device structure is realized through the use of fluorinated C60 as a p-dopant in a cross-linked hole transporting formulation. The lowering of the turn-on voltage is demonstrated using a conjugated peptide as the emitter layer. We suggest that fluorinated C60s could play a major role as tunable dopants in organic electronics.

Resonant free electron capture spectra of C60F48

Abstract Resonant electron capture spectra of C 60 F 48 and its oxy-analogue C 60 F 48 O have been studied and interpreted. Long-lived parent negative ions are formed within a 0–8 eV energy range with a maximum yield at approximately 0.14 eV. Going from thermal energy and up to 8 eV, these parent anions undergo fragmentation with generation of even-numbered fluorine negative ions due to sequential loss of F 2 down to C 60 F 36 − and C 60 F 36 O − , respectively; the yield of fragment anions at thermal energy rises with the degree of fragmentation. At approximately 8 eV and above, the odd-numbered fluorine fragment anions were registered. The formation of these anions in the energy range 17–45 eV was associated with the resonant state where the excitation of σ-plasmons is supposed to occur. The appearance energies of positive parent and fragment ions from C 60 F 48 as well as parent C 60 F 36 + have been measured. The parent ion C 60 F 48 − undergoes electron autodetachment at 3–4 eV with a mean lifetime in the millisecond scale. Estimations for CF bond dissociation energy and electron affinity of C 60 F 47 are reported. Published by Elsevier Science B.V.

Lifetime of negative molecular ions of tetracene and pentacene with respect to the autodetachment of an electron

The processes of nondissociative resonant attachment and autodetachment of electrons in a number of poly-cyclic aromatic hydrocarbon molecules have been investigated by mass spectrometry. Long-lived negative molecular ions of phenanthrene and triphenylene have not been observed. Such ions have been detected for anthracene, pyrene, and benzo[e]pyrene capturing thermal electrons. Negative molecular ions of tetracene and pentacene have also been observed up to 2.5–3 eV. The lifetimes of these ions with respect to the auto-detachment of an electron have been measured throughout the energy range where they are observed. This lifetime for tetracene and pentacene is more than 10 ms, which is two or three orders of magnitude larger than that for remaining compounds. Correlation between the lifetime of ions and the electron affinity of the molecules has been revealed.

Slow decay of negative molecular fluorofullerene ions in the electron autodetachment process

The mean lifetimes of negative molecular ions of C60 fullerene and its fluoroderivatives C60F18 and C60F36 with respect to the autodetachment of electrons have been measured as functions of the ionizing electron energy by the method of mass spectrometry of electron resonance capture. The lifetimes of negative ions in the compounds under investigation are within the one-second range, and an increase in the number of addends leads to an increase in the lifetimes of negative ions by 1.5–2.5 orders of magnitude.

In situ hydrogenation of C59N and resonant electron capture of C59NHx (x=0, 1 and 5)

The hydrogenation of the aza[60]fullerene C59N has been studied in situ. The C59N monomer is formed by thermal evaporation and dissociation of the (C59N)2 dimer and is hydrogenated in the heated inlet channel of a mass spectrometer, which is used subsequently for the product analysis. In addition to the expected formation of C59NH, the abundant production of C59NH5 is observed. Increasing the availability of hydrogen for the reduction enhances the formation of C59NH5, which is eventually obtained as the main product. The effective yield curves of the negative ions C59NHx−, where x=0, 1 and 5 are detailed and contrasted with the ion yields of C60Hx−, where x=0, 2 and 6. It is found that increasing hydrogen attainment reduces the energy range in which long-lived molecular ions can result from electron capture.

Processes of hydrogenation of trifluoromethylfullerenes in the mass spectrometer ion source

The processes of hydrogenation of a mixture of trifluoromethylfullerenes was studied in situ by means of positive-and negative-ion mass spectrometry. The effective addition of 1, 5, and 11 hydrogen atoms was revealed. The appearance energies of positive trifluoromethylfullerene ions C60 (CF3)n+ (n = 1–8) and C60(CF3)nH+ (n = 1, 3, 5, 7) were determined.

Formation of Doubly Charged Negative Ions under the Conditions of the Resonant Electron Capture by Fluorofullerenes

Doubly charged negative ions formed when electrons with controlled energies interact with isolated fluorinated fullerene molecules C60Fn (n = 36, 48) have been detected and investigated by resonant electron capture mass spectrometry. The dependence of the intensity of the formation of doubly charged negative ions of fluorofullerenes on the energy of attached electrons has been measured. An original method, which is based on the experimental data and does not require additional calibration quantities, has been developed for estimating the absolute cross section for the formation of doubly charged negative ions. The absolute cross sections for the formation of the most intensely formed ions C60F362− and C60F482− are estimated to be about 1.1 × 10−24 and 1.5 × 10−24 m2 at their maximum-yield energies of 2.0 and 1.6 eV, respectively.

The fragmentation of negative ions of fullerene C60 trifluoromethyl derivatives

The formation and decay of gas-phase negative ions of trifluoromethylated fullerenes C60(CF3)n(n = 2–10) were studied. The resonance electron capture mass spectra were measured to find that the main fragmentation channel of negative ions was the detachment of trifluoromethyl groups. The degree of fragmentation directly depended on the energy of electrons and reached the complete splitting off of all the CF3 addends with the formation of C60− ions. The observed metastable ion signals were analyzed to determine the scheme of sequential fragmentation of negative ions.

Formation of negative ions via resonant low-energy electron capture by cysteine and cystine methyl esters

The processes of resonance low-energy free electron attachment to methyl esters of some sulfur-containing amino acids were studied. The long-lived molecular negative ions of cystine dimethyl ester formed in the valence state via the Feshbach nuclear excited resonance mechanism were detected by mass spectrometry. The reactions of disulfide bond dissociation were identified in an electron energy range of 0—1 eV. They can be considered as model reactions regarding processes of peptide decomposition due to the resonance interaction with low-energy electrons. Predissociation of short-lived molecular ions of cysteine methyl ester formed by capture of electrons with energies of ~1.6 eV is accompanied by the intra-ionic transfer of negative charge from the carbonyl group to the sulfur atom leading to the elimination from the latter of hydrogen atom.