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Understanding Propyl-cyanide and its isomers formation: Ab initio Study of the Spectroscopy and Reaction Mechanisms

Abstract

Recent detection of propyl cyanide (C$_3$H$_7$CN) with both linear and branched structures has stimulated many experimental and theoretical studies. In this theoretical work, we present spectroscopic properties of the far infrared spectra of these species and we investigate their different paths of formation in gas phase. Our spectroscopic study concerns the far infrared spectra of both iso- and anti and gauche-normal propyl cyanide isomers. The equilibrium structures and the potential energy surfaces are calculated using explicitely correlated cluster ab initio methods (CCSD(T)-F12) and a variational procedure designed for non-rigid species and large amplitude motions. Accurate rotational constants, centrifugal distorsion constants, potential energy barriers and surfaces are provided. The ro-vibrational parameters in the ground vibrational states compare very well with experimental data. The low energy vibrational levels correspond to torsional modes. Far infrared energies are calculated up to 500 cm$^{-1}$ using the variational approach and the vibrational second order theory (VPT2), a good agreement with previous experimental values is found. We have also investigated the gas phase formation of the different C$_3$H$_7$CN isomers. After several trials of reacting gaseous species, we have found that one feasible formation route of the C$_3$H$_7$CN isomers can be from the bimolecular reaction of HCN with propene. At the UMP2(full)/aug-cc-pVTZ level of theory, this reaction involves two-steps for each isomer, the first one corresponds to the association of the two radicals while the second one corresponds to H transfer. From highly correlated ab initio calculations by means of CCSD(T)/aug-cc-pVTZ//UMP2(full)/aug-cc-pVTZ, the geometries, energetics and minimum energy paths of the reactions are obtained. Also, the first step' transition state disappears, as the diradical minimum is much less stabilized with UCCSD(T) than by UMP2(full). We employ the zero curvature tunneling and canonical variational (CVT/ZCT) semiclassical method to predict rate constants for propyl cyanide isomers formation in gas phase.

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Publication details

The article was received on 06 Aug 2019, accepted on 01 Oct 2019 and first published on 02 Oct 2019


Article type: Paper
DOI: 10.1039/C9CP04365A
Phys. Chem. Chem. Phys., 2019, Accepted Manuscript

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    Understanding Propyl-cyanide and its isomers formation: Ab initio Study of the Spectroscopy and Reaction Mechanisms

    B. Kerkeni, V. Gámez, M. L. Senent and N. Feautrier, Phys. Chem. Chem. Phys., 2019, Accepted Manuscript , DOI: 10.1039/C9CP04365A

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