Dynamic of negative ions in potassium-D-ribose collisions

D.A. and F. F. S. acknowledge the Portuguese Foundation for Science and Technology (FCT-MEC) for a post-graduate Grant No. SFRH/BD/61645/2009 and post-doctoral Grant No. SFRH/BPD/68979/2010, respectively. We are also grateful to the partial funding from the Portuguese research Grant Nos. PEst-OE/FIS/UI0068/2011 and PTDC/FIS-ATO/1832/2012 through FCT-MEC. P.L.-V. acknowledges his visiting professor position at The Open University, UK. The Spanish Ministerio de Economia y Competitividad (Project No. FIS 2012-31230) is also acknowledged. Some of this work forms part of the EU/ESF COST Actions Nano-IBCT-MP1002 and The Chemical Cosmos-CM0805.We present negative ion formation from collisions of neutral potassium atoms with D-ribose (C5H10O5), the sugar unit in the DNA/RNA molecule. From the negative ion time-of-flight (TOF) mass spectra, OH- is the main fragment detected in the collision range 50-100 eV accounting on average for 50% of the total anion yield. Prominence is also given to the rich fragmentation pattern observed with special attention to O- (16m/z) formation. These results are in sharp contrast to dissociative electron attachment experiments. The TOF mass spectra assignments show that these channels are also observed, albeit with a much lower relative intensity. Branching ratios of the most abundant fragment anions as a function of the collision energy are obtained, allowing to establish a rationale on the collision dynamics. (C) 2013 AIP Publishing LLC.publishersversionpublishe