Dimerization of methanimine and its charged species in the atmosphere of Titan and interstellar/cometary ice analogs

Abstract

Aims. We theoretically investigated the dimerization of methanimine, CH 2 =NH, a process that has been invoked to explain the formation of haze in the atmosphere of Titan and nitrogen organic compounds in interstellar/cometary ice analogs. Methods. We used density functional theory to characterize the minima and transition states of the investigated processes, while we computed the energetics with the more accurate coupled cluster method. We then obtained rate coefficients via combination of capture theory and statistical calculations. Results. The process involving two neutral molecules is characterized by significant energy barriers and cannot occur under the low temperature conditions of Titan or interstellar/cometary ices unless an external energy source is provided. On the contrary, the processes involving one molecule of either ionized or protonated methanimine are barrierless reactions and can therefore contribute to the formation of larger ions. In particular, the reaction involving ionized methanimine can also be efficient in the very low temperature conditions of the interstellar medium, leading to products of general formula C 2 N 2 H + .Conclusions. The present work suggests that polymerization of methanimine is not an efficient process in space unless an ionization/protonation or a significant energy source is available.

Angular Distribution of Ion Products in the Double Photoionization of Propylene Oxide

“…In order to clarify this qualitative speculation it should be highly helpful to perform further theoretical calculations on the structure and energetic stability of the intermediate propylene oxide dication, as well as of all possible ionic species that can be formed following its unimolecular two-body fragmentation by Coulomb explosion. Similar calculations have been carried out in our laboratory for simpler systems (Teixidor et al, 2003; Candori et al, 2007; Leonori et al, 2009a,b; Rosi et al, 2012; Skouteris et al, 2015).…”

“…After the pioneering work of Hipple concerning the spontaneous dissociation processes of ions (Hipple, 1948), the importance of the fragmentation dynamics following single and double photodissociation photoionization processes has been investigated in a number of papers, respectively by R. N. Zare, who first fully described the dynamics of molecular photodissociation (Zare and Herschbach, 1962, 1963; Zare, 1972; Greene and Zare, 1982), and by J. H. D. Eland et al (Eland and Treves-Brown, 1992; Field and Eland, 1993; Eland, 2006). Following such basic contributions, various authors contributed to this Research Topic (Fišer et al, 2009; Price et al, 2017), also highlighting the role of singly and doubly charged ions in the chemistry of upper planetary atmospheres (Thissen et al, 2011; Falcinelli et al, 2014, 2016a) and in space (Ascenzi et al, 2004; Bartolomei et al, 2008; Skouteris et al, 2015). Furthermore, dissociation dynamics of multiply charged ions has been studied [see for example Geronés et al and references therein (Geronés et al, 2007)] with related implications on chemistry of the interstellar medium (Geronés et al, 2012).…”

Molecular Dications in Planetary Atmospheric Escape

“…The presence of CO 2 , N 2 O in the ISM has been demonstrated by microwave spectroscopy, whereas C 2 H 2 was detected by IR spectroscopic measurements [33]. Acetylene is also found as a minor component in the atmosphere of gas giants like the planet Jupiter, in the atmosphere of Saturn's satellite Titan, and in comets, where photochemical experiments have demonstrated that this simple hydrocarbon is a likely precursor of C 2 , a widely observed component in such environments [45][46][47][48].…”

An Experimental and Theoretical Investigation of 1-Butanol Pyrolysis

“…The potential energy surface of the species of interest was calculated employing a computational strategy which has already been utilized with success in several cases (see, for instance Leonori et al, 2009a,b; de Petris et al, 2011; Rosi et al, 2012; Skouteris et al, 2015; Troiani et al, 2017). In this scheme the lowest stationary points were optimized at the B3LYP (Becke, 1993; Stephens et al, 1994) level of theory in conjunction with the correlation consistent valence polarized set aug-cc-pVTZ (Dunning, 1989; Kendall et al, 1992).…”