Electronic Excitations and Low-Energy Electron-Induced Scattering Studies of Acrylonitrile (CH₂CHCN)

Abstract

We report here theoretical investigations on structural, spectroscopic, and electron scattering for acrylonitrile (CH2CHCN), a molecule of importance in astrochemistry as well as the chemical industry. Quantum chemical calculations for ground and excited states are performed using density functional theory (DFT) and time-dependent-DFT methods, respectively. The results of geometry optimization and vibrational frequencies agree well with data available in the literature, while vertical excited singlet-state energies are extended to higher excited states as compared to earlier studies, including Rydberg and valence excitations. Quantum defect analysis and comparison of the theoretically predicted energies with earlier reported experimental works led to the confirmation of some spectral assignments and the revision of a few assignments. Vibrational frequencies calculated for the cationic ground state are used to tentatively assign vibrational bands appearing along with the Rydberg transitions. Triplet excited-state energies for which no data is available in the literature are reported here for the first time. Low-energy (0.1 to 20 eV) electron scattering calculations are performed using the ab initio R-matrix method. Several types of resonances are predicted in the energy-dependent elastic cross-section, most of which are in good agreement with earlier experimental or theoretical works, while a few new resonances are found above 6 eV. Additionally, calculations of eigenphase sum, differential, momentum transfer, electronic excitation, ionization, and total cross-sections are being reported for the first time. This work represents a comprehensive theoretical study of the electronically excited states as well as low-energy electron scattering of acrylonitrile, which would be useful for understanding its chemistry in the interstellar medium as well as industrial applications.

Theoretical Investigation of Dissociative Electron Attachment of Acrylonitrile

“…As stated earlier, the low-energy feature in DEA is primarily caused by electron capture in one of the LUMOs as a one-particle shape resonance. The existing dissociation peak at 1.5 eV can be thus correlated with one-particle shape resonance observed at 1.4 eV in our previous cross-sectional study on acrylonitrile …”

“…Looking into the importance of the various anion formation channels of acrylonitrile, we attempt to compute here DEA cross-sections for the two most probable dissociation channels of acrylonitrile (CN – and C 3 N – ). This is our attempt to compute DEA for acrylonitrile which is in continuation of the work published earlier . Along with that, we have also calculated the rate coefficient of various processes.…”

“…The resonance positions and widths obtained here are used for the DEA cross-section calculations. More details about the R-matrix method are given in earlier publications, ,,− and the methodology employed for DEA cross-section calculations , is explained in brief below and can also be found in the report by Munro et al…”

“…Figure2c), while Figure2brepresents the π bonding nature of the highest occupied molecular orbital (HOMO). This LUMO π* antibonding above the CN bond is primarily responsible for resonances below 3 eV.34 Due to this attachment of electrons, energy is transferred from the π CN bond to the σ CC bond in nitriles as a result of cleavage over the C2−C4 bond17 (Figure2a).The present DEA on CN − shown in Figure3is calculated using bond dissociation energy B(C 2 H 3 −CN) = 5.4 eV,17 electron affinity (CN) = 3.82 eV,17 and vibrational frequency 882 cm −1 21. As seen in Figure3, the CN − ion starts appearing at a very low energy around 1.5 eV.…”

Theoretical Investigation of Electron Impact Scattering on Imidazole

“…However, to make calculations easier, this electron scattering problem was carried out with a fixed nuclei approach using the UK polyatomic R -matrix code driven by the Quantemol-N system . The R -matrix theory is a well-known scattering approach, and its application to electron–molecule scattering has been thoroughly discussed in Tennyson’s report and in our previous publications. − Hence, we present a brief description of the theoretical approach to avoid repetition.…”