Dissociative Recombination of Astrochemically Interesting Ions

University dissertation from Stockholm : Department of Physics, Stockholm University

Abstract: In this thesis the major work described concerns experimental determination of the dissociative recombination (DR) reaction for several molecular ions of astrochemical interest. DR is the process where an electron recombines with a molecular ion to form an excited neutral that disintegrates into two or more neutral fragments to release the gained excess energy. It is very efficient under cold conditions and therefore ubiquitously occurring in interstellar environments such as dark clouds and plays an important role in aeronomical plasmae, lightnings and in man-made plasmas such as in combustion engines and fusion reactors. Although DR reactions are crucial processes in all these environments, product branching fractions of DR reactions have proven to be very unpredictable and present one of the great remaining challenges for theoreticians. The experimental work includes determination of reaction rates and product distribution of DR of complex ions such as protonated alcohols and ethers. The following species have been investigated and are discussed in this thesis:CH3OH2+ (protonated methanol), CD3OD2+ (deuteronated methanol), CD3OCD2+ (methoxymethyl cation), CD3CDOD+ (deuteronated acetaldehyde), CH3CH2OH2+ (protonated ethanol) and (CD3)2OD+ (deuteronated dimethyl ether).The results of these measurements are used in astrochemical model calculations in which the rates used hitherto greatly have been based on educated guesses. Employing the outcome of the DR investigations of the CH3OH2+ and CD3OD2+ ions have shown a great impact on such models. The DR investigations have been followed up by astronomical observations. Theoretical models and laboratory experiments show that methanol should be formed from CO on cold grains. This scenario was tested by astronomical observations of gas associated with young stellar objects (YSOs). Two independent tests were showing consistency with methanol formation on grain surfaces.