SO3 formation from the X-ray photolysis of SO2 astrophysical ice analogues: FTIR spectroscopy and thermodynamic investigations

Author(s)

Bonfim, Victor de Souza ^[1] ; de Castilho, Roberto Barbosa ^[2] ; Baptista, Leonardo ^[3] ; Pilling, Sergio ^{[1, 4]}

Affiliation

^[1] Univ Vale Paraiba UNIVAP, Lab Astroquim & Astrobiol LASA, Sao Jose Dos Campos, SP - Brazil

^[2] Univ Fed Rural Rio de Janeiro, Dept Quim, Seropedica, RJ - Brazil

^[3] UERJ, Resende, RJ - Brazil

^[4] ITA DCTA, Inst Tecnol Aeronaut, Sao Jose Dos Campos, SP - Brazil

• Document type: Journal article
• Source: Physical Chemistry Chemical Physics; v. 19, n. 39, p. 26906-26917, OCT 21 2017.
• Web of Science Citations: 3

Abstract

In this combined experimental-theoretical work we focus on the physical and chemical changes induced by soft X-rays on sulfur dioxide (SO2) ice at a very low temperature, in an attempt to clarify and quantify its survival and chemical changes in some astrophysical environments. SO2 is an important constituent of some Jupiter moons and has also been observed in ices around protostars. The measurements were performed at the Brazilian Synchrotron Light Source (LNLS/CNPEM), in Campinas, Brazil. The SO2 ice sample (12 K) was exposed to a broadband beam of mainly soft X-rays (6-2000 eV) and in situ analyses were performed by IR spectroscopy. The X-ray photodesorption yield (upper limit) was around 0.25 molecules per photon. The values determined for the effective destruction (SO2) and formation (SO3) cross sections were 2.5 x 10(-18) cm(2) and 2.1 x 10(-18) cm(2), respectively. The chemical equilibrium (88% of SO2 and 12% of SO3) was reached after the fluence of 1.6 x 10(18) photons cm(-2). The SO3 formation channels were studied at the second-order Moller-Plesset perturbation theory (MP2) level, which showed the three most favorable reaction routes (Delta H < - 79 kcal mol(-1)) in simulated SO2 ice: (i) SO + O-2 -> SO3, (ii) SO2 + O -> SO3, and (iii) SO2 + O+ -> SO3+ + e(-) -> SO3. The amorphous solid environment effect decreases the reactivity of intermediate species towards SO3 formation, and ionic species are even more affected. The experimentally determined effective cross sections and theoretical reaction channels identified in this work allow us to better understand the chemical evolution of certain sulfur-rich astrophysical environments. (AU)

• FAPESP's process: 09/18304-0 - Synthesis and degradation of prebiotic molecular species at planetary atmospheres, comets and interstellar ice analogs
• Grantee: Sergio Pilling Guapyassu de Oliveira
• Support Opportunities: Research Grants - Young Investigators Grants