Abstract
The results of a detailed study of the photodissociation of carbon cluster ions, C +3 to C +20 , are presented and discussed. The experiments were performed using internally cold cluster ions derived from pulsed laser evaporation of a graphite target rod in a helium buffer gas followed by supersonic expansion. The mass selected clusters were photodissociated using 248 nm and 351 nm light from an excimer laser. Photofragment branching ratios, photodissociation cross sections and data on the laser fluence dependence of photodissociation are reported. For almost all initial clusters, C + n , the dominant photodissociation pathway was observed to be loss of a C3 unit to give a C + n−3 ion. This observation is interpreted as indicating that dissociation occurs by a statistical unimolecular process rather than by direct photodissociation. The photodissociation was found to be linear with laser fluence forn>5 with 248 nm and 351 nm light; quadratic forn=5 for 248 nm and 351 nm; and linear forn=4 at 248 nm. Dissociation energies for the carbon cluster ions implied by these results are discussed. The photodissociation cross sections were found to change dramatically with cluster size and with the wavelength of the photodissociating light.
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The absolute scale is derived from the dimensions of the photodissociating laser beam at the point of photodissociation. The laser beam goes through a small aperature just before entering the vacuum system and appears homogeneous at the point of photodissociation. For clusters with large photodissociation cross sections we were able to deplete the parent by >80% with large laser fluences which indicates that there is good overlap between the cluster ion packet and the photodissociating laser beam. The absolute scale is probably reliable to within a factor of two
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On leave from Institute of Physical Sciences and Technology, University of Maryland, College Park, MD 20742, USA
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Geusic, M.E., Jarrold, M.F., McIlrath, T.J. et al. Photofragmentation of mass resolved carbon cluster ions. Z Phys D - Atoms, Molecules and Clusters 3, 309–317 (1986). https://doi.org/10.1007/BF01384821
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DOI: https://doi.org/10.1007/BF01384821