Structure, Stability, and Spectroscopic Properties of Small Acetonitrile Cation Clusters

Abstract

Ionization and fragmentation pathways induced by ionizing agents are key to understanding the formation of complex molecules in astrophysical environments. Acetonitrile (CH 3 CN), the simplest organic nitrile, is an important molecule present in the interstellar medium. In this work, DFT and MP2 calculations were performed in order to obtain the low energy structures of the most relevant cations formed from electron-stimulated ion desorption of CH 3 CN ices. Selected reaction pathways and spectroscopic properties were also calculated. Our results indicate that the most stable acetonitrile cation structure is CH 2 CNH + and that hydrogenation can occur successively without isomerization steps until its complete saturation. Moreover, the stability of distinct cluster families formed from the interaction of acetonitrile with small fragments, such as CH n + , C 2 H n + , and CH n CNH + , is discussed in terms of their respective binding energies. Some of these molecular clusters are stabilized by hydrogen bonds, leading to species whose infrared features are characterized by a strong redshift of the N− H stretching mode. Finally, the rotational spectra of CH 3 CN and protonated acetonitrile, CH 3 CNH + , were simulated using distinct computational protocols based on DFT, MP2, and CCSD(T) considering centrifugal distortion, vibrational−rotational coupling, and vibrational anharmonicity corrections. By adopting an empirical scaling procedure for calculating spectroscopic parameters, we were able to estimate the rotational frequencies of CH 3 CNH + with an expected average error below 1 MHz for J values up to 10.

Bimolecular reactions of CH2CN2+ with Ar, N2 and CO: reactivity and dynamics

“…[112][113][114] In addition the energetics and geometries we derive are in good agreement with recent computational studies. 115 Calculations were also employed to determine the energy of the lowest energy structure of the HC 2 N + monocation formed when the dication loses a proton. The lowest energy state of HC 2 N + determined from these calculations is a doublet that has a linear N-C-C geometry, with the H bonded to the terminal C slightly off the N-C-C axis.…”

“…112–114 In addition the energetics and geometries we derive are in good agreement with recent computational studies. 115…”

A spectral survey of CH3CCH in the Hot Molecular Core G331.512-0.103

“…Aside from observational advantages, the intrinsic spectroscopic properties of CH 3 CCH can directly affect the observed spectra and therefore can give powerful insights on the physics of the emitting gas. Rotational spectroscopy is a conspicuously fruitful technique to infer information on the molecular species and its environment (e.g., Domenicano & Hargittai 1992;Winnewisser et al 2003;Grubbs & Cooke 2010), and is nowadays highly assisted by quantum-chemistry (e.g., Puzzarini et al 2012b,a;Cernicharo et al 2015;McGuire et al 2016;Cazzoli et al 2016;Cerqueira et al 2020;Santos et al 2020). The rotational Hamiltonian is described in terms of the zeroth-order rotational constants (A, B, and C), and the higher-order centrifugal-distortion constants (e.g., D J , D JK , D K , H J , H JK , H KJ and H K , for symmetric tops).…”

Multiply charged naphthalene and its C10H8 isomers: bonding, spectroscopy, and implications in AGN environments

“…In addition to fragmentation processes, the ionisation of small cycles, including aromatic rings, can induce molecular isomerisation (Jašík et al 2015;Monfredini et al 2016;Fantuzzi et al 2018;Quitián-Lara et al 2018;Monfredini et al 2019;Fantuzzi et al 2019;Wolff et al 2020), which is usually accompanied by a severe loss of molecular integrity. Several examples were demonstrated by screening the potential energy surface (PES) of a given molecular structure for each charge state under consideration (Jašík et al 2015;Fantuzzi et al 2018;Gutsev et al 2020;Hendrix et al 2020;Cerqueira et al 2020). For benzene, the basic unit of PAHs, the six-membered ring structure is the global minimum for the neutral and singly charged states, but the dicationic singlet ground state has an unusual pentagonal-pyramidal geometry (Krogh-Jespersen 1991;Jašík et al 2014Jašík et al , 2015Fantuzzi et al 2017;Wolff et al 2020;Pozo-Guerron et al 2020).…”