The interstellar chemistry is very vivid and complex with many interconnected chemical reactions. The chemical networks that lead to the formation of interstellar molecules in interstellar and circumstellar regions form the backbone of astrochemistry. This thesis works towards getting more insights on the gas-phase dynamics of the interstellar medium (ISM) and provide information for better astrochemical models by building experimental set-ups for laboratory astrophysics and examining the dissociation and ionization dynamics of selected molecules of astrophysical relevance.
Anion detection in the astrophysical environments is very challenging. So far only six anions have been detected in the interstellar and circumstellar regions, and out of which three are nitrogen terminated carbon chain anions (CnN-). The thesis presents the first study on the dissociation dynamics of CnN- (n=1-3,5-7) anions in ISM and CSM and identifies three more new physico-chemical processes that anions can take part in interstellar and circumstellar regions. This work answers one of the important questions, namely how these anions, especially small ones in this series, are formed in the regions where they are detected. The results reveal the possible presence of two new anions, namely C2- and C2N-, in the outer envelope of the carbon-rich star IRC +10216 and the thesis call for the search of these species. In another work, the dissociation pathways of FeO molecule upon dissociative electron attachment (DEA) in Sagittarius B2 (Sgr B2) are identified and a call for the search of Fe- and O- in Sgr B2 is made. As part of this thesis work, a new experimental setup was developed to perform multiphoton ionization and dissociation (MPI/MPD) experiments on polycyclic aromatic hydrocarbon (PAH) molecules of astrophysical interests. The formation of small hydrocarbons via dissociative ionization of PAH molecules, specifically anthracene, phenanthrene and pentacene, in the presence of intense UV field (multiphoton regime) were explored with this setup and the results revealed a wealth of information of astrophysical importance. In another significant work, 22-pole radiofrequency ion-trap experimental setup was built and commissioned with aims to do temperature-dependent reaction rate studies of ion-neutral reactions and lifetime studies of short lived anions of astrophysical relevance. The setup has exciting applications in a range of fields like ion-physics, physical chemistry, atmospheric chemistry, biochemistry etc.