Proton interactions with interstellar and atmospheric molecules are of great interest in many fields of study and are relevant to interstellar medium and earth’s stratosphere. When the solar flare occur, the solar windcarry protons, the main constituent, with high kinetic energy in the range of 1–2 keV enter the earth’s ionosphere. High energy protons transfer their kinetic energy due to collisions with various molecules present in the region resulting in inelastic, charge transfer and reactive processes. Chemistry of interstellar medium (ISM) is different from the conventional study of chemical reactions. Temperature of ISM is as low as 2 K and understanding of chemical reactivity demands cold state specific cross sections. Astrochemical models need data in the broad region of temperatures to understand the reactivity and knowledge of abundance of detected species. The analysis of observed spectra and estimation of abundance often require collisional excitation and deexcitation rate coefficients. Quantum dynamics study of ion-neutral energy transfer process widens the understanding the molecular composition and kinetics of ISM.