Photoionization of C4 molecular beam:: Ab initio calculations

Large computations are performed on the C-4(+) cation in order to characterize its stable isomers and its lowest electronic excited states using configuration interaction methods and large basis sets. Several stable isomers are found including a linear C-4(+)(l-C-4(+)), a rhombic C-4(+)(r-C-4(+)) (or cyclic), and a branched (d-C-4(+)) structure. Our calculations show a high density of electronic states for all of these isomers favoring their interactions. By combining the present ab initio data and those on neutral C-4, the l-C-4(X)+h nu -> l-C-4(+)(X+)+e(-), d-C-4(X)+h nu -> d-C-4(+)(X+)+e(-), and r-C-4(X)+h nu -> r-C-4(+)(X+)+e(-) vertical photoionization transition energies are computed at 10.87, 10.92, and 10.77 eV, respectively. Photoionizing a C-4 molecular beam results on an onset at 10.4-10.5 eV and then to a linear increase of the signal due to the opening of several ionization channels involving most of the C-4 and C-4(+) isomers and electronic states. (c) 2007 American Institute of Physics.