Amorphous Ammonia–Water Ice Deposited onto Silicate Grain: Effect on Growth of Mantles Ice on Interstellar and Interplanetary Dust

Abstract

The interaction of molecules on the mineral surface is interesting in understanding the development of icy mantles on interstellar and interplanetary dust. The ice grains can freeze and cover the silicate cores, growing an amorphous ice mantle. In the interstellar medium, olivine is a silicate that has been found in many places in dust. Previously we have simulated the interaction between amorphous water ice and forsterite surface. In this work we describe a more realistic situation, by adding ammonia molecules in a model of amorphous dirty ice onto forsterite surface. The NH 3 is a part of the volatile components of cometary and interstellar ices. We propose models that describe a mixture of amorphous ice (ammonia−water) and forsterite ( 100) surfaces (dipolar and nondipolar). Our quantum mechanical calculations show that the ammonia has a similar affinity (30 kcal/mol) to the forsterite surface as that of water (31 kcal/mol). We calculated also the infrared frequencies to characterize the most reactive sites in the chemisorption processes. We observed important frequency shifts related to the position of the main vibrational modes of the NH 3 moieties, which react chemically with the mineral surface.

DFT study of electronic and redox properties of TiO2 supported on olivine for modelling regolith on Moon and Mars conditions

“…In addition, the bidentate binuclear mode changed the coordination of the neighbor Mg atoms from 4f to 2f (Mg 68 and Mg 138 ). Similar behavior was observed in other previous adsorption studies on forsterite surfaces (Escamilla-Roa et al, 2017Escamilla-Roa and Moreno, 2012;Escamilla-Roa and Sainz-Díaz, 2014). As a result of these strong alterations on the surface, the adsorption energy indicates an exothermic process (À29.08 eV).…”

Adsorption of 5-aminosalicylic acid on kaolinite surfaces at a molecular level

“…The convergence criterion for the self-consistent field was 1 × 10 –6 . The geometry optimizations of various structures were performed at 0 K. This methodology has been used previously to describe the adsorption process successfully (Escamilla-Roa et al , 2014, 2017). In order to estimate the contribution of the weak van der Waals interactions in the adsorption complexes, corrections with the semi-empirical formalisms of Tkatchenko & Scheffler (2009) or Grimme (2006) for weak dispersion forces were included in some optimizations.…”

Volatile Abundances, Extended Coma Sources, and Nucleus Ice Associations in Comet C/2014 Q2 (Lovejoy)

“…It is also worth considering whether the high affinity of H 2 CO, NH 3 , and C 2 H 2 with H 2 O could form either hydrogen bonds or clusters in ices that would decrease the volatility of these complexes compared with pure molecular ices (e.g., Tzeli et al 2000;Duvernay et al 2014;Escamilla-Roa & Sainz-Diaz 2014). The identities and importance of potential additional sources of C 2 H 2 , H 2 CO, and NH 3 in comets need further study, and observational opportunities on comets that can address this should be prioritized, as well as comet sample return missions that can preserve these potential semivolatile sources.…”