Evaporation rates for liquid clusters

Frauendorf, S.

doi:10.1007/bf01437069

Cited by 35 publications

(27 citation statements)

References 14 publications

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“…When the fragment is a single particle, as for emission of atoms, electrons and photons, the fragment level density reduces to a single degeneracy factor g due to the spin or polarization of the particle. For photon emission the spectral emission rate is (Hansen and Campbell 1998) Downloaded by [New York University] at 09:06 10 June 2015 and for emission of electrons and atoms (Bertsch et al 1991, Frauendorf 1995, Frobrich 1995, Hervieux and Gross 1995 The reduced mass of the channel, in practice the electron or atom mass, is denoted by m. When electrons are emitted, the charge state of the cluster is changed but the number of vibrational degrees of freedom remains unchanged. When an atom is emitted, the situation is reversed; the daughter has three less degrees of freedom but the same charge state.…”

Section: Decay Channelsmentioning

confidence: 99%

“…The idea Downloaded by [New York University] at 09:06 10 June 2015 that we shall use here is a variant of that used by Frauendorf (1995), where bulk values of free energies and surface tensions were used to obtain level densities through an inversion of the partition function. We shall invert that approach and simplify it by postulating that the cluster level densities are of the harmonic oscillator type and compare the evaporation rates of this parametrization with the bulk values in the form of vapour pressure data in order to judge the validity of the approach.…”

Section: Decay Channelsmentioning

confidence: 99%

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Statistical emission processes of clusters

Hansen

1999

Philosophical Magazine B

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Section: Decay Channelsmentioning

confidence: 99%

Section: Decay Channelsmentioning

confidence: 99%

Statistical emission processes of clusters

Hansen

1999

Philosophical Magazine B

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“…From decay rate theory in the framework of the Weisskopf model [15,36,37], the slope s n of the energydependence is given by [14] …”

Section: Decay Pathway Branching Ratiosmentioning

confidence: 99%

Photodissociation of small group-11 metal cluster ions: Fragmentation pathways and photoabsorption cross sections

Vogel

Herlert

Schweikhard

2003

J. Am. Soc. Mass Spectrom.

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Noble metal cluster ions Cu n ϩ , Ag n ϩ and Au n ϩ (n ϭ 3-21) have been stored in a Penning trap and photodissociated by low intensity laser pulses of 10 ns at photon energies of 3.49 eV and 4.66 eV. The fragmentation pathways, neutral monomer and dimer evaporation, have been monitored as a function of cluster size, excitation energy and element. It is found that the behavior of the branching ratio between monomer and dimer evaporation as a function of excitation energy depends on the metal under investigation. In particular, the slope of the energy dependence is positive for silver but negative for gold and copper cluster ions. Furthermore, photoabsorption cross sections are determined from observed total fragment yields in single-photon dissociation. (J Am Soc Mass Spectrom 2003, 14, 614 -621)

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“…For atom evaporation a rate closely analogous to the Weisskopf rates for neutron emission from hot nuclei is found [16][17][18],…”

mentioning

confidence: 79%

“…(2)-(4) are found by extrapolation from bulk values as in [17,18]: The heat capacity of vanadium between 298 and 2190 K is [24] C P ͑T ͒ n eff ͑b 1 2cT ͒ ,…”

mentioning

confidence: 99%

Radiative Cooling of a Small Metal Cluster: The Case ofV13+

et al. 1999

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Size-selected stored metal cluster ions, V 1 13 , have been heated by photoexcitation (l 730 to 229 nm) to well-defined excitation energies corresponding to temperatures between 1000 and 2100 K. A millisecond pump-probe photodissociation technique was applied to measure the time-resolved radiative cooling. The observed decay rates are directly related to the radiative energy loss and are explained quantitatively by the competing processes of photoemission and atom evaporation. PACS numbers: 36.40.Vz, 44.40. + a, 82.80.Ms Radiative cooling of clusters can be regarded as the microscopic analog of black body radiation. However, in contrast to a macroscopic black body the wavelength of the emitted light exceeds the dimension of its source (the cluster) considerably. Furthermore due to the small heat capacity of clusters, the light emission is suppressed for these particles at high photon energies. Although these effects yield a modification of Planck's law the resulting emission spectra are still smooth as observed in the case of refractory metal clusters (W,Re,Nb) [1,2] and C 60 [3]. In order to obtain sufficient signal intensity in the metal cluster studies, it was necessary to work with a broad distribution of cluster sizes. In addition, the internal energy of the radiating clusters was not well defined. Only in the case of carbon clusters [4] and C 60 , where macroscopic amounts are available, radiative cooling of a single cluster size has been investigated [5][6][7][8], however in all cases for broad thermal distributions.In this Letter we present an alternative approach to measure radiative cooling of clusters. It is based on the storage of clusters in a Penning trap and subsequent photoabsorption which allows one to prepare an ensemble of one cluster size at a well-defined temperature. Their radiative cooling is monitored time resolved via its influence on the fragmentation behavior. The data are compared to a Monte Carlo simulation, where atom and photon emission is described by phase space theory [9] and also multiple photon emission is taken into account.The Mainz Cluster Trap [10] combines an external ion source with a Penning trap-time-of-flight (TOF) mass spectrometer [11]. For the present measurements positively charged clusters are produced by laser vaporization of a vanadium wire and condensation in a helium gas pulse. They are guided towards a Penning trap and stored by a superposition of a homogeneous magnetic field (B 5 T) for radial and an electric quadrupole field for axial confinement (potential well of 1.5 eV). From the ensemble of captured vanadium cluster ions V 1 13 is mass selected by radial ejection of all other ions. The V 1 13 ions are centered by a combination of buffer gas collisions and quadrupolar excitation [12] and confined within a region of about 1.8 mm diameter in the middle of the trap [13].In this process the clusters undergo some 300 collisions with argon atoms and equilibrate to a canonical ensemble at room temperature corresponding to E 0 0.53͑14͒ eV internal energy. The...

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Evaporation rates for liquid clusters

Cited by 35 publications

References 14 publications

Statistical emission processes of clusters

Statistical emission processes of clusters

Photodissociation of small group-11 metal cluster ions: Fragmentation pathways and photoabsorption cross sections

Radiative Cooling of a Small Metal Cluster: The Case ofV13+

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