Electron-driven molecular processes for cyanopolyacetylenes HC2n+1N (n = 3, 4, and 5)

Abstract

Linear carbon series cyanopolyacetylenes (HC_2n+1N) (n = 3, 4, and 5) are astromolecules found in the atmosphere of Titan and interstellar media such as TMC-1 (Taurus molecular cloud-1). All these compounds are also detected in IRC + 10 216. In the present work, we comprehensively investigate electron interaction with important cyanopolyacetylene compounds, viz. HC₇N (cyano-tri-acetylene), HC₉N (cyano-tetra-acetylene), and HC₁₁N (cyano-penta-acetylene). The study covers incident electron energies ranging from the ionization threshold to 5 keV. Various electron-driven molecular processes are quantified in terms of total cross-sections. The quantum spherical complex optical potential (SCOP) is used to determine elastic (Q_el) and inelastic (Q_inel) cross-sections. Ionization is the most important inelastic effect that opens various chemical pathways for the generation of different molecular species; we computed the ionization cross-section (Q_ion) and discrete electronic excitation cross-section (ΣQ_exc) using the complex scattering potential-ionization contribution (CSP-ic) method. The cyanopolyacetylene compounds are difficult to handle experimentally owing to the health risks involved. Therefore, there are no prior experimental data available for these molecules; only Q_ion have been reported theoretically. Thus, the present work is the maiden report on computing Q_el, Q_inel, ΣQ_exc, and Q_T. In order to provide an alternative approach and further validation of the present work, we employed our recently developed two-parameter semi-empirical method (2p-SEM) to compute Q_el and Q_T. Additionally, we predict the polarizability of the HC₁₁N molecule, which has not been reported in the existing literature. This prediction is based on a correlation study of polarizabilities of molecules with Q_ion values from the same series of molecules.