I t is demonstrated that anisotropies can exist in the angular distributions of dissociative ions produced from a polyatomic molecule by electron impact. In particular, the distributions of 0 ' and CO+ ions from CO, are found to exhibit anisotropies for incident electron energies close to their respective production thresholds. The same symmetry arguments previously used to qualitatively explain similar anisotropies in the case of diatomic molecules can also be used in this case. The C + angular distribution is found to be essentially isotropic.The cross sections for the production of CO:, CO', 0 ' and C c are obtained for incident electron energies up to 300 eV. Large discrepancies exist between these cross section values and those obtained in other recent experiments.It is shown that predissociation via the C state is not a dominant mechanism for the production of fragment ions.

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PACS. 36.20.-r -Macromolecules and polymer molecules. PACS. 87.15.-v -Biomolecules: structure and physical properties. PACS. 47.50.+d -Non-Newtonian fluid flows.Abstract. -We investigate the stretching of a polymer in a uniform flow using molecular dynamics (MD) simulations. Our MD simulations represent an ab-initio experiment with no explicit assumption for the dynamics of a single chain except for using the generic Lennard-Jones and the FENE potentials. In spite of the modest length of our simulated chains, the qualitative features of experiments on DNA are reproduced and the predictions of a wormlike chain theory are found to hold, with the polymer molecule being free draining at large extensions.c EDP Sciences

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