Decay of C60 by delayed ionization and C2 emission: experiment and statistical modeling of kinetic energy release.

C(60) molecules highly excited in the nanosecond regime decay following ionization and dissociation by emitting a series of carbon dimers, as well as other small fragments if excitation is strong enough. The fragmentation mass spectrum and kinetic energy release of all charged fragments obtained in these experiments are interpreted within the framework of the Weisskopf theory, using a realistic Monte Carlo procedure in which the rates of all relevant decay channels are modeled using Arrhenius expressions. Comparison between the measurements and the simulated spectra allows the distribution of deposited energy to be accurately estimated. The dependence of the fragment kinetic energies on the laser fluence, found in the simulation but not observed in the experimental results, indicates that the small fragments are not necessarily emitted from small fullerenes resulting from C(60) by sequential decay. Rather, direct multifragmentation of C(60) is invoked to interpret the observed patterns. The possible role of post-ionization of neutral emitted fragments is discussed.

Translational, rotational and vibrational energy partitioning in the sequential loss of carbon dimers from fullerenes.

The sequential thermal dissociation of up to five carbon dimers from neutral, singly and doubly charged C(60) molecules is theoretically investigated in the framework of phase space theory. Using a semiclassical treatment of vibrations and rotations, we quantify the amount of kinetic energies released in the form of translation, rotation, and vibration under realistic experimental conditions. Our results reveal that translational and vibrational energies of the dimers are nearly equilibrated after a few emissions, whereas the rotational contribution lies far below equipartition. An approximate treatment in which dimers are rotationally and vibrationally frozen essentially leads to the same conclusions.

Vibrational Structure of the (2)1Sigma+u-X(1)1Sigma+g Transition of the Ba2 Molecule.

Resonant two photon ionization (R2PI) technique was used to obtain the excitation spectrum of the Ba2 molecule. A group of 12 vibrational bands was found in the 740-764 nm region. As a result of mass selective detection, they were attributed unambiguously to the Ba2 molecule. By comparison to recent theoretical calculations, those bands were assigned to the (2)1Sigma+u-X(1)1Sigma+g transition; they may be fitted to give the following vibrational constants (in cm-1): omega"e = 33.2 +/- 0.2, omega"ex"e = 0.5 +/- 0.2, omegae = 65.2 +/- 0.2, and omega'ex'e = 0.4 +/- 0.2. Copyright 1998 Academic Press.