Quantum chemical study on the formation of isopropyl cyanide and its linear isomer in the interstellar medium

Abstract

The formation mechanism of linear and isopropyl cyanide (hereafter n-PrCN and i-PrCN, respectively) in the interstellar medium (ISM) has been proposed from the reaction between some previously detected small cyanides/cyanide radicals and hydrocarbons/hydrocarbon radicals. n-PrCN and i-PrCN are nitriles therefore, they can be precursors of amino acids via Strecker synthesis. The chemistry of i-PrCN is especially important since it is the first and only branched molecule in ISM, hence, it could be a precursor of branched amino acids such as leucine, isoleucine, etc. Therefore, both n-PrCN and i-PrCN have significant astrobiological importance. To study the formation of n-PrCN and i-PrCN in ISM, quantum chemical calculations have been performed using density functional theory at the MP2/6-311++G(2d,p)//M062X/6-311+G(2d,p) level. All the proposed reactions have been studied in the gas phase and the interstellar water ice. It is found that reactions of small cyanide with hydrocarbon radicals result in the formation of either large cyanide radicals or ethyl and vinyl cyanide, both of which are very important prebiotic interstellar species. They subsequently react with the radicals CH2 and CH3 to yield n-PrCN and i-PrCN. The proposed reactions are efficient in the hot cores of SgrB2 (N) (where both n-PrCN and i-PrCN were detected) due to either being barrierless or due to the presence of a permeable entrance barrier. However, the formation of n-PrCN and i-PrCN from the ethyl and vinyl cyanide always has an entrance barrier impermeable in the dark cloud; therefore, our proposed pathways are inefficient in the deep regions of molecular clouds. It is also observed that ethyl and vinyl cyanide serve as direct precursors to n-PrCN and i-PrCN and their abundance in ISM is directly related to the abundance of both isomers of propyl cyanide in ISM. In all the cases, reactions in the ice have smaller barriers compared to their gas-phase counterparts.

Kinetics of CN (v = 1) reactions with butadiene isomers at low temperature by cw-cavity ring-down in a pulsed Laval flow with theoretical modelling of rates and entrance channel branching

“…Although the present results are consistent with earlier conclusions that pyridine formation is unlikely in these reactions, the fast reaction rates and the dominance of CN-substituted unsaturated products formed implies the above reactions could be prominent elementary steps in systematic growth of more complex nitrogen-containing compounds detected in the ISM. [1][2][3][4]52,53 Although differing in density and collision frequency by many orders of magnitude, these same reactions are certainly important in the chemistry of planetary atmospheres, such as that of Titan, which possess rich chemistry driven by energetic processing of the dense N 2 -CH 4 atmosphere. [54][55][56] Nitriles and unsaturated hydrocarbons are abundant, leading to the formation of aerosol haze layers that have been the subject of intense investigation for decades, while analogous hazes on exoplanets frustrate interrogation of their atmospheres.…”

Survey of Monocot ethno-medicinal plants in Purba Medinipur, Paschim Medinipur and Jhargram districts of West Bengal, India

“…Garrod (2013) showed that the subsequential hydrogenation of HC 3 N in the free-fall collapse phase can form the vinyl cyanide (CH 2 CHCN) (HC 3 N + 2H → CH 2 CHCN). The subsequential hydrogenation of the CH 2 CHCN form C 2 H 5 CN in the grain surface of the hot molecular cores and high-mass protostars (CH 2 CHCN + 2H → C 2 H 5 CN; Garrod 2013), through barrierless and exothermic radical-radical reactions (Singh et al 2021). This particular chemical reaction is demonstrated to be the most efficient way for the formation of C 2 H 5 CN towards the Sgr B2, G10.47+0.03, G31.41+0.31, and other molecular cores (Belloche et al 2009;Manna & Pal 2023;Mininni et al 2023).…”

Study of Complex Nitrogen and Oxygen-bearing Molecules toward the High-mass Protostar IRAS 18089–1732

“…, is formed on the grain surface of high-mass protostars and hot molecular cores (see Mehringer et al 2004;Garrod 2013;Garrod et al 2017Garrod et al , 2022. Garrod (2013) showed that the subsequential hydrogenation of HC 3 N in the freefall collapse phase can form vinyl cyanide (CH CHCN ; Garrod 2013), through barrierless and exothermic radical-radical reactions (Singh et al 2021). This particular chemical reaction is demonstrated to be the most efficient way for the formation of C H CN 2 5 toward Sgr B2, G10.47+0.03, G31.41+0.31, and other molecular cores (Belloche et al 2009;Manna & Pal 2023;Mininni et al 2023).…”