Organic substances in cometary grains: comparison of secondary ion mass spectral data and californium-252 plasma desorption data from reference compounds

Secondary ion mass spectra (SIMS) and Cf-252 plasma desorption ionization mass spectra (PDMS) of two carboxylic acids and two purine nucleobases have been compared. Results demonstrate that the positive ion mass spectra as well as the negative ion mass spectra are very similar in SIMS and PDMS. The principal characteristics are formation of quasimolecular ions (M + H)(+) or (M-H)(-) and loss of small molecules producing nonradical fragment ions; fumaric acid exhibits a remarkable formation of radical cations and anions. A set of simplified rules has been formulated for typical ion production processes involved in these techniques. This work contributes to the development of methods for data interpretation applicable to in situ analyses of cometary grains during the ROSETTA space mission of European Space Agency to the comet 46p/Wirtanen. (C) 1999 Elsevier Science B.V.