2026-09-20T00:02:27Zhttps://iris.unitn.it/oai/request

oai:iris.unitn.it:11572/3684362026-04-03T00:46:07Zcom_11572_237821com_11572_101871col_11572_237822ou_ou00011

Dissociative charge transfer of organic molecules induced by collisions with the He+ cation. A joint experimental and theoretical study of relevance for the interstellar medium evolution Cernuto, Andrea Cernuto, Andrea Ascenzi, Daniela Settore FIS/01 - Fisica Sperimentale Settore CHIM/02 - Chimica Fisica Collisions with He+ are an important pathway for the destruction of complex organic molecules in the interstellar medium (ISM). We have carried out dissociative charge transfer reactions of He+ with two oxygen containing organic molecules, ubiquitous in ISM: dimethyl ether (DME, CH3OCH3 ) and methyl formate (MF, HCOOCH3). Since they have a prebiotic relevance, several models were developed to explain how these molecules are formed and destroyed in the ISM. The reactions have been investigated by using the home-built Guided-Ion Beam Mass Spectrometer (GIB-MS) apparatus. Absolute cross sections and branching ratios of the products have been measured as a function of the collision energy in the hyperthermal energy range (i.e. from about 0.1 eV to 7 eV). The presence of the molecular ion was not observed among the products for these reactions, which means that the nascent DME and MF radical cations are formed in a dissociative state. Insights on both the charge transfer processes have been obtained by investigating the nature of the non-adiabatic transitions between the reactant and product potential energy surfaces (PES). The PES has been represented by using a semi-empirical method to model the inter-molecular interactions. To explain the experimental evidence, two excited states of DME and MF radical cations have been invoked: He+ captures an electron from inner valence orbitals of both the organic molecules, having binding energies ~10 eV higher than the HOMO. An improved Landau-Zener-StÃ1⁄4ckelberg model has been developed to obtain the total integral cross-section to be compared with the experimental results. Inter-molecular interaction and electron densities of the orbitals involved in the reaction turned out to be key points to describe the dynamics of the two studied dissociative charge transfers. A very good agreement is obtained between the experimental and calculated total cross-sections at low collision energy, which is the most relevant range for the interstellar environment. These results represent a significant starting point to estimate rate constants for the total dissociation of DME and MF by collisions with He+ ions in the ISM at low temperatures. 2017 info:eu-repo/semantics/doctoralThesis https://hdl.handle.net/11572/368436 http://dx.doi.org/10.15168/11572_368436 10.15168/11572_368436 eng firstpage:1 lastpage:169 numberofpages:169 info:eu-repo/semantics/openAccess Università degli studi di Trento place:TRENTO license:Tutti i diritti riservati (All rights reserved) license:Tutti i diritti riservati (All rights reserved) license uri:iris.PRI01