On the concept of temperature for a small isolated system

Andersen, J. U.; Bonderup, E.; Hansen, Klavs

doi:10.1063/1.1357794

Cited by 184 publications

(139 citation statements)

References 11 publications

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“…75 If the microcanonical heat capacities C n of the cluster ions are approximated by the equipartition theorem, C n = (3n -7)k B , one can derive a quantitative relation between relative dissociation energies D n / D n and relative ion abundances A n / A n , where the tilded quantities are functions that are obtained by fitting smooth functions to D n and A n , respectively. 76 Normalization to these smooth functions is needed because local anomalies in the ion abundance provide information about local variations in D n , not about global trends.…”

Section: Abundance Anomalies and Adsorption Of H 2 On Graphitic Sumentioning

confidence: 99%

Adsorption of hydrogen on neutral and charged fullerene: Experiment and theory

Kaiser

Leidlmair

Bartl

et al. 2013

The Journal of Chemical Physics

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A consistent and accurate ab initio parametrization of density functional dispersion correction (DFT-D) for the 94 elements H-Pu The Journal of Chemical Physics 132, 154104 (2010) Helium droplets are doped with fullerenes (either C 60 or C 70 ) and hydrogen (H 2 or D 2 ) and investigated by high-resolution mass spectrometry. In addition to pure helium and hydrogen cluster ions, hydrogen-fullerene complexes are observed upon electron ionization. The composition of the main ion series is (H 2 ) n HC m + where m = 60 or 70. Another series of even-numbered ions, (H 2 ) n C m + , is slightly weaker in stark contrast to pure hydrogen cluster ions for which the even-numbered series (H 2 ) n + is barely detectable. The ion series (H 2 ) n HC m + and (H 2 ) n C m + exhibit abrupt drops in ion abundance at n = 32 for C 60 and 37 for C 70 , indicating formation of an energetically favorable commensurate phase, with each face of the fullerene ion being covered by one adsorbate molecule. However, the first solvation layer is not complete until a total of 49 H 2 are adsorbed on C 60 + ; the corresponding value for C 70 + is 51. Surprisingly, these values do not exhibit a hydrogen-deuterium isotope effect even though the isotope effect for H 2 /D 2 adsorbates on graphite exceeds 6%. We also observe doubly charged fullerene-deuterium clusters; they, too, exhibit abrupt drops in ion abundance at n = 32 and 37 for C 60 and C 70 , respectively. The findings imply that the charge is localized on the fullerene, stabilizing the system against charge separation. Density functional calculations for C 60 -hydrogen complexes with up to five hydrogen atoms provide insight into the experimental findings and the structure of the ions. The binding energy of physisorbed H 2 is 57 meV for H 2 C 60 + and (H 2 ) 2 C 60 + , and slightly above 70 meV for H 2 HC 60 + and (H 2 ) 2 HC 60 + . The lone hydrogen in the odd-numbered complexes is covalently bound atop a carbon atom but a large barrier of 1.69 eV impedes chemisorption of the H 2 molecules. Calculations for neutral and doubly charged complexes are presented as well.

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Section: Abundance Anomalies and Adsorption Of H 2 On Graphitic Sumentioning

confidence: 99%

Adsorption of hydrogen on neutral and charged fullerene: Experiment and theory

Kaiser

Leidlmair

Bartl

et al. 2013

The Journal of Chemical Physics

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“…In order to express the rate constant in Arrhenius form, we expand the logarithm of the level density around the average energy E − E b /2. Combining all the factors in front of the level density ratio in equation (A.1) into a frequency ν, we then obtain [14,31],…”

Section: Appendix Amentioning

confidence: 99%

“…A statistical equilibrium of an isolated molecule can be represented by a microcanonical ensemble of molecules with fixed excitation energy E, and a microcanonical temperature may be introduced, defined by the relation 1/k B T = d/dEρ(E), where ρ(E) is the level density and k B Boltzmann's constant [31]. For the large fullerene molecules, it can with sufficient accuracy be calculated as the temperature T of a canonical ensemble with average excitation energy equal to E. Even at excitation energies of 10-20 eV, the range relevant for our experiments, the temperature is moderate and hence nearly all the energy resides in vibrations.…”

Section: Depletion and Coolingmentioning

confidence: 99%

Radiative cooling of fullerene anions in a storage ring

Andersen

Gottrup

Hansen

et al. 2001

The European Physical Journal D

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Abstract. Thermionic emission from hot fullerene anions, C − N , has been measured in an electrostatic storage ring for even N values from 36 to 96. The decay is quenched by radiative cooling and hence the observations give information on the intensity of thermal radiation from fullerenes. The experiments are analysed by comparison with a simulation which includes the quantisation of photon energy and the statistics of emission. Experiments with heating of the molecules with a laser beam confirm the interpretation of the observations in terms of radiative cooling and give an independent estimate of the cooling rate for C − 60 . The measured cooling rates agree in general within a factor of two with the prediction from a classical dielectric model of a thermal radiation intensity of ∼ 300 eV/s for C60 at 1 400 K, scaling approximately with the 6th power of the temperature and with the number of atoms in the molecule. PACS

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“…8. In this case, similar to [13], the finite-heat-bath correction [19,20] is taken into account by setting τ −1 (T ) = A exp(−E a /k B T * ), where T * = T − E a /2C [the microcanonical heat capacity is assumed to be C = (3n − 6)k B , where n = 20N]. As seen in Our next aim is to analyze the stability of two-dimensional and three-dimensional systems based on the C 20 fullerenes, which will be done in a future work.…”

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confidence: 99%