Ion-molecule reactions of ammonia clusters with C60 aggregates embedded in helium droplets
Helium nanodroplets are co-doped with C60 and ammonia. Mass spectra obtained by electron ionization reveal cations containing ammonia clusters complexed with up to four C60 units. The high mass resolution of Δm/m ≈ 1/6000 makes it possible to separate the contributions of protonated, unprotonated and dehydrogenated ammonia. C60 aggregates suppress the proton-transfer reaction which usually favors the appearance of protonated ammonia cluster ions. Unprotonated Cx(NH3)n+ ions (x = 60, 120, 180) exceed the abundance of the corresponding protonated ions if n < 5; for larger values of n the abundances of C60(NH3)n+ and C60(NH)n−1NH4+ become about equal. Dehydrogenated C60NH2+ ions are relatively abundant; their formation is attributed to a transient doubly charged C60–ammonia complex which forms either by an Auger process or by Penning ionization following charge transfer between the primary He+ ion and C60. The abundance of CxNH3+ and CxNH4+ ions (x = 120 or 180) is one to two orders of magnitude weaker than the abundance of ions containing one or two additional ammonia molecules. However, a model involving evaporation of NH3 or NH4 from the presumably weakly bound CxNH3+ and CxNH4+ ions is at odds with the lack of enhancement in the abundance of C120+ and C180+. Mass spectra of C60 dimers complexed with water complement a previous study of C60(H2O)n+ recorded at much lower mass resolution.
Physical Chemistry Chemical Physics
Royal Society of Chemistry
Digital Object Identifier (DOI)
H. Schöbel, C. Leidlmair, P. Bartl, S. Denifl, O. Echt, T. D. Märk, and P. Scheier, Ion-molecule reactions of ammonia clusters with C60 aggregates embedded in helium droplets, Phys.Chem.Chem.Phys. 13 (2011) 1092-1098, DOI:10.1039/C0CP01268H