Gas phase electronic spectroscopy of ionic carbon chains, rings, fullerenes and analogues

Abstract

Low temperature gas phase electronic spectra of ionic carbon chains, rings, fullerenes and analogues are presented. These data were obtained through action spectroscopy experiments using a cryogenic radiofrequency ion trapping apparatus. Action spectra of C2n+ (n = 4−14) monocyclic carbon ring cations were recorded by helium tagging. A linear shift of the origin band wavelength of the lowest energy electronic transition of this series with increasing ring size was observed. The potential relevance of these cyclic structures to astrochemical environments is discussed. Higher energy electronic transitions of C20+ were also recorded using a two colour fragmentation approach to obtain data on the bare ion. Theoretical calculations were carried out to support the assignment of a C5+ electronic transition observed in the visible. It was found that DFT is not appropriate to calculate the electronic structure of this small open-shell linear carbon cation. CASPT/ccpvdz and NEVPT2/ccpvtz calculations were used to optimise the electronic structure and calculate the electronic transitions. CCSD(T) single point energy calculations support the identification of the lowest energy geometry. The electronic spectrum of C60+ synthesised in a laser vaporisation source is presented and compared with that of C60+ generated from a commercial sample by electron impact. The source conditions were optimised for C60+ in order to synthesise metallo fullerenes of astrochemical interest. Mass spectra of first attempts to synthesise Na+@C60 are also presented. Electronic spectra of the endohedral fullerenes H2O@C60+ and D2O@C60+ are presented. These data were obtained by one-photon dissociation of weakly bound helium complexes synthesised in a 3K ion trap. The spectra are compared with the electronic transition of the empty C60+ cage, shown to be responsible for several DIBs. The spectrum of H2O@C60+ is found to be much richer in structure, composed of features assigned to rotational excitation of H2O accompanying the electronic transition of the C60+ cage. Two-colour experiments were used to separate contributions from ortho- and para-H2O@C60+ nuclear spin isomers stored in the trap. The obtained data from measurement on H2O@C60+ were compared with D2O@C60+ providing insight into the nature of the transitions observed in the spectra