RESUMO

Organic molecules are a potential source of prebiotic chemistry in the interstellar medium (ISM). Methanol (MetOH) is a very important source of more complex molecules. H3 O+ (aq) and Cl- (aq) are fundamental to living organisms and can be generated in the ISM from the dissociation of HCl with just four water molecules, yielding the (H3 O)+ (H2 O)3 Cl- ion-pair. Here, a detailed mechanism, based on density functional theory (DFT) and ab-initio (2nd order Mϕller-Plesset perturbation theory, MP2) calculations, is suggested for the substitution reactions of these water molecules by MetOH. The time required for formation of an appreciable amount of the product ((H3 O)+ (MetOH)3 Cl- ) can be only few years. Such reaction can take place in Sagittarius B2, where HCl, H2 O and MetOH have already been identified and it can be an important source for the formation of more complex prebiotic structures.

Assuntos

RESUMO

The effect of water molecule on the excited states of CH3Cl(H2O), as compared to those of the isolated chloromethane, has been studied at the multireference configuration interaction with singles and doubles (MR-CISD), including extensivity corrections. Eight new Rydberg states are due to the water molecule but the common states of both systems are not severely altered. Potential energy curves of 23 singlet states along the C-Cl coordinate have also been computed at the MR-CISD level. The dissociation energy of the C-Cl bond decreases from ∼0.4 to 0.5 eV due to the water molecule. As for CH3Cl (de Medeiros, V. C., J. Am. Chem. Soc. 2016, 138, 272-280), a stable ion-pair has also been characterized. However, for CH3Cl(H2O), this ion-pair is better described as a solvent-shared semi-ion-pair, CH3+δ(H2O)Cl-δ. This species is connected with three ionic dissociation channels, with two being due to the water molecule. The presence of these new ionic channels, particularly the lowest energy one, [H3C-O]+ + Cl-, raises a very important question of atmospheric relevance: can the interaction of chloroalkanes with water decrease its deleterious effect on the ozone layer? Several potentially new competing dissociation channels are also studied. The latter results can help to set up the most important states to be included in nonadiabatic dynamic calculations to study how the yields of the ionic channels change due to the water molecule.