Size dependent reaction kinetics of small gold clusters with carbon monoxide: Influence of internal degrees of freedom and carbonyl complex stability

The reactions of free gold clusters Au^–, , and with carbon monoxide are studied in an rf-octopole ion trap experiment at cryogenic temperatures. While Au^– is unreactive toward CO over the whole temperature range investigated, the two and three atom cluster anions show a maximum adsorption of two CO molecules at temperatures below 250 K. From time resolved trapping experiments the strongly cluster size dependent reaction kinetics are obtained and a distinct reaction mechanism is deduced. The size dependence of the measured rate coefficients reveals the preferred formation and particular stability of the carbonyl complex . Through RRK analysis of the absolute termolecular rate coefficients we are able to estimate the binding energy of CO to and .     

Dependence of negative ion formation on inhomogeneous electric field strength in atmospheric pressure negative corona discharge

The dependence of negative ion formation on the inhomogeneous electric field strength in atmospheric pressure negative corona discharge with point-to-plane electrodes has been described. The distribution of negative ions HO^-, NO_x ^- and CO_x ^- and their abundances on the plane electrode was obtained with a mass spectrometer. The ion distribution on the plane was divided into two regions, the center region on the needle axis and peripheral region occurring the dominant NO_x ^- and CO_x ^- ions and HO^- ion, respectively. The calculated electric field strength in inhomogeneous electric field established on the needle tip surface suggested that the abundant formation of NO_x ^- and CO_x ^- ions and HO^- ion is attributed to the high field strength at the tip apex region over 10⁸ Vm^-1 and the low field strength at the tip peripheral region of the order of 10⁷ Vm^-1, respectively. The formation of HO^-, NO_x ^- and CO_x ^- has been discussed from the standpoint of negative ion evolution based on the thermochemical reaction and the kinetic energy of electron emitted from the needle tip.     

Multiple ionization and fragmentation of the DNA base thymine by interaction with C q+ ions

Ionization and fragmentation of the DNA base thymine upon interaction with keV C^q+ ions (q = 1 - 6) has been studied. By means of time-of-flight spectrometry of two or more thymine fragments in coincidence with an ejected electron we could investigate particular dissociation channels by means of their associated kinetic-energy-release. The fragmentation dynamics are strongly influenced by the C^q+ charge state: for low q values mainly fragmentation due to direct collisions is observed. With increasing q, electron capture becomes more important. For larger q we could identify several Coulomb explosion channels, leading to very energetic fragments.