The electron and nuclear dynamics of C60 fullerenes
irradiated with femtosecond laser pulses are investigated with
photoelectron and photoion spectroscopy. The focus of this work is
the detailed exploration of the population mechanism of Rydberg
levels within the excitation process of neutral C60. The effect
of excitation wavelength, intensity, chirp, and polarization on the
kinetic energy distribution of photoelectrons in single-pulse
experiments gives first insight into the underlying processes. In
combination with time-resolved two-color pump-probe spectroscopy
depending on either pump, or probe pulse intensity, a more complete
picture of the interaction can be drawn. The results point towards a
very interesting but nevertheless complex behavior including four
steps: (i) non-adiabatic multielectron excitation of the HOMO
(hu) → LUMO+1 (t1g) transition; (ii)
thermalization within the hot electron cloud on a time scale below
100 fs, followed by a coupling of energy to vibrational modes of
the molecule via doorway state(s); (iii) population of
electronically excited Rydberg states by multiphoton absorption, and
(iv) single photon ionization from the excited Rydberg states. This
excitation process results in a characteristic sequence of
photoelectron lines in the photoemission spectra. The comparison of
the experimental results with recent theoretical work gives
convincing evidence that non-adiabatic multielectron dynamics (NMED)
plays a key role for the understanding of the response of C60
to short-pulse laser radiation. 相似文献
We present calculated results for the optimization highly-charged fragment ion formation in the Coulomb explosion of I2 in an intense laser field. Calculations are performed using a simple genetic algorithm and a classical model for the Coulomb explosion process. We find that at low intensity the production of highly-charged fragment ions is optimized by a Fourier-limited pulse, whereas at higher intensity the Coulomb explosion is optimized by a sequence of pulses, with a time-separation determined by enhanced ionization at the critical internuclear distance. Our calculations provide insight into the sensitivity of adaptive pulse shaping experiments to the parameters and evolutionary approaches used.Received: 6 January 2003, Published online: 15 July 2003PACS:
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states) - 82.53.Eb Pump probe studies of photodissociation - 02.60.Pn Numerical optimization 相似文献
The photoionization of the C60 and C240 fullerenes by ultrashort electromagnetic pulses of subfemtosecond duration is studied. The probability for the process to occur during the action of the pulse as a function of the pulse duration is calculated for different carrier frequencies. The spectrum of photoelectrons emitted during the ionization of the fullerenes by a pulse with a corrected Gaussian shape is calculated. 相似文献
Polymer-C60 fullerene composite coatings are studied using thermal desorption mass spectrometry. It is found that thermal desorption spectra of C60 fullerene molecules can exhibit several resolved peaks (at a specified heating rate) corresponding to thermal desorption states. The relative intensity of the thermal desorption peaks depends on the procedure used for preparing the composite coatings, in particular, on the time of sedimentation of the polymer-fullerene suspension. The occurrence of different stages in thermally stimulated desorption of C60 fullerene molecules is explained by the fact that the fullerene molecules can exist in several phase states characterized by different densities and degrees of ordering in the polymer matrix. 相似文献
The interaction of a 60 fs 790 nm laser pulse with beams of Ar+, C+, H2+, HD+ and D2+ are discussed. Intensities up to 1016 Wcm-2 are employed. An experimental z-scanning technique is used to resolve the intensity dependent processes in the confocal volume.Received: 6 January 2003, Published online: 15 July 2003PACS:
32.80.Fb Photoionization of atoms and ions - 33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states) - 42.50.Hz Strong-field excitation of optical transitions in quantum systems; multiphoton processes; dynamic Stark shift 相似文献
The stability of C60 and C70 fullerenes and C60 and C72 nanotubes devoid of 2–12 atoms of the cluster skeleton was theoretically studied. It was established that Cn molecules with an even number of atoms remain stable, which was confirmed by experimental studies of monomolecular decay of clusters with the number of atoms n≥30. The change in the internuclear distances and in the ionization potential of nanoclusters was determined depending on the number of eliminated atoms. Such defects were shown to decrease the ionization potential of nanoclusters by 0.5–0.8 eV. The electron spectrum was calculated within the Harrison semiempirical tight-binding model in the Goodwin modification. A new parametrization of interatomic matrix elements of the Hamiltonian and atomic terms for carbon nanoclusters was suggested. 相似文献
C(2)-H exchange incis-[(en)2Co(HIm)(enH)]Br4 (Im, imidazole; en, ethylenediamine) was studied over a pD range of 9.4 to 10.2 at 60°C where thecis-[(en)2Co(Him)(enH)]4+ andcis-[(en)2Co(HIm)(en)]3+ are the species present in significant concentrations.Cis-[(en)2Co(HIm)(enH)]4+ has pKa1 7.86 and pKa2 9.82 with pKa1 corresponding to coordinated enH ionization and pKa2 to ImH ionization. The kinetic data may be interpreted in terms of an intramolecular H-D exchange mechanism, where the “dangling”-ND2CH2CH2ND2 group acts as a base to remove the imidazole C(2)-H proton from the coordinated DIm moiety. 相似文献
A series of new heterofullerides with compositions Rb2MC60, K2MC60, and KM2C60 (M = Mg, Be) have been synthesized. Measurements of the temperature dependences of the magnetic susceptibility in the temperature interval from 4.2 to 300 K reveal a superconducting transition in heterofullerides K2MgC60, KMg2C60, K2BeC60, and Rb2BeC60 at temperatures Tc = 13–22 K. The electron states with uncompensated spin are studied by the electron paramagnetic resonance technique. The contributions of conduction electrons and localized electrons to the paramagnetic susceptibility are extracted. 相似文献
Resonance-enhanced multiphoton ionization combined with electronic ground state depletion spectroscopy of jet-cooled 2-methylallyl (C4H7) radicals provides vibronic spectra of the 3s and 3p Rydberg states. Analysis of the vibronic structure following one-photon and two-photon excitation of rovibronically cold 2-methylallyl radicals and its isotopologues C4H4D3 and C4D7 reveals transitions to more than 30 vibrational levels in the 3s Rydberg state that are identified and reassigned on the basis of predictions from ab initio calculations and results from pulsed-field-ionization zero-kinetic-energy photoelectron spectra obtained with resonant multiphoton excitation via selected intermediate states. Depletion spectroscopy reveals transitions to short-lived 3p Rydberg states that have a large oscillator strength. 相似文献
Absolute cross-sections for electron-impact dissociative ionization of C2
H2+ and C2 D2+ to CH+, C+, C2+ , H+, CH2+
and C2D+ fragments are determined for electron energies ranging
from the corresponding threshold to 2.5 keV. Results obtained in a crossed
beams experiment are analyzed to estimate the contribution of dissociative
ionization to each fragment formation. The dissociative ionization cross
sections are seen to decrease for more than an order of magnitude, from
CH+ (5.37±0.10) × 10-17 cm2 over C+ (4.19±
0.16) × 10-17 cm2, C2D+ (3.94±0.38) ×
10-17 cm2, C2+ (3.82±0.15) × 10-17 cm2
and H+ (3.37±0.21) × 10-17 cm2 to CH2+
(2.66±0.14) × 10-18 cm2. Kinetic energy release
distributions of fragment ions are also determined from the analysis of the
product velocity distribution. Cross section values, threshold energies and
kinetic energies are compared with the data available from the literature.
Conforming to the scheme used in the study of the dissociative excitation of
C2H2+
( C2 D2+ )\left( {\rm C}_2 {\rm D}_2^+ \right), the cross-sections are presented in
a format suitable for their implementation in plasma simulation codes. 相似文献
Absolute cross-sections for electron-impact ionization and dissociation of
C2H2+ and C2D2+ have been measured for electron energies
ranging from the corresponding thresholds up to 2.5 keV. The animated
crossed beams experiment has been used. Light as well as heavy fragment ions
that are produced from the ionization and the dissociation of the target
have been detected for the first time. The maximum of the cross-section for
single ionization is found to be (5.56 ± 0.03)× 10-17 cm2 around 140 eV. Cross-sections for dissociation of C2
H2+ (C2D2+) to ionic products are seen to decrease for two orders
of magnitude, from C2D+ (12.6 ± 0.3) × 10-17 cm2 over CH+(9.55 ± 0.06) × 10-17 cm2,
C+ (6.66 ± 0.05) × 10-17 cm2, C2+ (5.36 ± 0.27) × 10-17 cm2, H+ (4.73 ±
0.29) × 10-17 cm2 and CH2+ (4.56 ± 0.27) × 10-18 cm2 to H2+ (5.68 ± 0.49) ×
10-19 cm2. Absolute
cross-sections and threshold energies have been compared with the scarce
data available in the literature. 相似文献
The electrical conductivity of C60 single crystals is found to increase by 55–120% under β irradiation with low doses. It is shown that this effect can be associated with multistage collision ionization of C60 molecules. 相似文献
The structure of the fullerence fluoride C60F24 of the Th symmetry contains two types of chemically different carbon atoms, namely, atoms of isolated double bonds and atoms of CF groups. X-ray photoelectron and x-ray emission spectroscopic studies of C60F24 revealed a difference in the widths of the x-ray bands corresponding to these types of atoms. Nonempirical quantum-chemical calculations performed for C59NF24+ ions with a hole in the C 1s core level of the fullerence fluoride showed that the difference in the bandwidths may be due to the fact that the vibrational states of the system are different when 1s electrons are removed from chemically nonequivalent atoms. 相似文献
Thin films of fullerenes (C60) were deposited onto silicon using matrix-assisted pulsed laser evaporation (MAPLE). The deposition was carried out from
a frozen homogeneous dilute solution of C60 in anisole (0.67 wt%), and over a broad range of laser fluences, from 0.15 J/cm2 up to 3.9 J/cm2. MAPLE has been applied for deposition of fullerenes for the first time and we have studied the growth of thin films of solid
C60. The fragmentation of C60 fullerene molecules induced by ns ablation in vacuum of a frozen anisole target with C60 was investigated by matrix-assisted laser desorption/ionization (MALDI). Our findings show that intact fullerene films can
be produced with laser fluences ranging from 0.15 J/cm2 up to 1.5 J/cm2. 相似文献
Carbon-based nanoparticles (NPs) such as fullerenes and nanotubes have been extensively studied for drug delivery in recent years. The permeation process of fullerene and its derivative molecules through membrane is essential to the utilization of fullerene-based drug delivery system, but the mechanism and the dynamics of permeation through cell membrane are still unclear. In this study, coarse-grained molecular dynamics simulations were performed to investigate the permeation process of functionalized fullerene molecules (ca. 0.72 nm) through the membrane. Our results show that single functionalized fullerene molecule in such nanoscale could permeate the lipid membrane in micro-second time scale. Pristine C60 molecules prefer to aggregate into several small clusters while C60OH15 molecules could aggregate into one big cluster to permeate through the lipid membrane. After permeation of C60 or its derivatives into membrane, all C60 and C60OH15 molecules disaggregated and monodispersed in the lipid membrane.
Absolute cross sections for electron-impact single ionization, dissociative
excitation and dissociative ionization of the ethynyl radical ion
(C2D+)^+) have been measured for electron energies ranging from the
corresponding reaction thresholds to 2.5 keV. The animated crossed
electron-ion beam experiment is used and results have been obtained for the
production of C2D2+, C2+, C2+_2^+ , CD+, C+ and
D+. The maximum of the cross section for single ionization is found to
be (2.01 ± 0.02) × 10-17 cm2, at the incident electron
energy of 105 eV. Absolute total cross sections for the various singly
charged fragments production are observed to decrease by a factor of almost
three, from the largest cross-section measured for C+, over C2+_2^+
and CD+ down to that of D+. The maxima of the cross sections are
obtained to be (14.5 ± 0.5) × 10-17 cm2 for C2+_2^+,
(12.1 ± 0.1) × 10-17 cm2 for CD+, (27.7 ±
0.2) × 10-17 cm2 for C+ and (11.1 ± 0.8) × 10-17 cm2 for D+.
The smallest cross section is measured to
be (1.50 ± 0.04) × 10-18 cm2 for the production of the
doubly charged ion C2+. Individual contributions for dissociative
excitation and dissociative ionization are determined for each
singly-charged product. The cross sections are presented in closed analytic
forms convenient for implementation in plasma simulation codes. Kinetic
energy release distributions of dissociation fragments are seen to extend
from 0 to 6 eV for the heaviest fragment C2+_2^+, up to 11.0 eV for
CD+, 14.2 eV for C+ and 11.2 eV for D+ products. 相似文献
A semi-empirical molecular dynamics model is developed. The central collisions of C60+C60 and He@C60+He@C60 at different incident energies are investigated based on this model. It is found that the dimer structures have been produced
at proper incident energies and these fullerene dimers could be formed by a self-assembly of C60 fullerene and He@C60. The He atom has a significant effect at higher incident energy and this embedded He atom can enhance the stability of the
dimer structure. 相似文献