A theoretical study of three gas-phase reactions involving the production or loss of methane cations

Abstract

Hydrocarbon ions are important species in flames, spectroscopy and the interstellar medium. Their importance is reflected in the extensive body of literature on the structure and reactivity of carbocations. However, the geometry, electronic structure and reactivity of carbocations are difficult to assess. This study aims to contribute to the current knowledge of this subject by presenting a quantum mechanics description of methane cation dissociation using multiconfigurational methods. The geometric and electronic parameters of the minimum structure were determined for three main reaction paths: the dissociation CH4(+)→ CH2(+) + H2 and the dissociation-recombination processes CH4(+)↔ CH3(+) + H. The electronic and energetic effects of these reactions were analyzed, and it was found that each reaction path has a strong dependence on the methodology used as well as a strong multiconfigurational character during dissociation. The first doublet excited states are inner-shell excited states and may correspond to the ions that are expected to be formed after electron detachment. The rate coefficient for each reaction path was determined using variational transition state theory and RRKM/master equation calculations. The major dissociation paths, with their rate coefficients at the high-pressure limit, are CH4(+)(X(~)(2)B1) → CH3(+)(A(2)A1') + H((2)S) (k∞(T) = 1.42 × 10(+14) s(-1) exp(-37.12/RT)) and CH4(+)(X(~)(2)B1) → CH2(+)(A(2)A1) + H2((2)Σg(+)) (k∞(T) = 9.18 × 10(+14) s(-1) exp(-55.77/RT)). Our findings help to explain the abundance of ions formed from CH4 in the interstellar medium and to build models of chemical evolution.

Feasibility of novel (H3C)nX(SiH3)3−ncompounds (X = B, Al, Ga, In): structure, stability, reactivity, and Raman characterization from ab initio calculations

“…In all reactions studied in this work (involving the triels), the calculated heights of the energy barriers (20.10-78.83 kcal mol −1 ) are in agreement with the energy barriers calculated in other similar studies. [53][54][55] Moreover, these barriers are in line with those calculated for the kinetics of the group 13 trihy- drides. 56 This finding may indicate the feasibility of the chemical synthesis for these compounds, under typical MOCVD conditions of high temperatures and general thermodynamic disequilibrium.…”

“…The (H 3 C)B(SiH 3 ) 2 compound interact with silane to form one additional bonding B-SiH 3 , while an H atom is detached from SiH 4 and temporarily occupies a site between the two silyl groups (see reactants and the adduct formation in Fig. [53][54][55] Moreover, these barriers are in line with those calculated for the kinetic of the group 13 trihydrides. This adduct gives rise to a first-order TS (ν i = 807.9i cm -1 ), leading to the formation of the reaction products B(SiH 3 ) 3 + CH 4 by overcoming an energy barrier of 21.19 kcal/mol.…”