Computational study on structure and electron affinities of carbon-containing triatomic molecules

Abstract

The accurate measurement and calculation of molecular electron affinity has been a hot topic. The existing theoretical study does not consider the effects of different basic sets, or various correlation effects or zero point energy correction. In addition, there are some deviations of calculation results from experimental measurements. Therefore, we conduct a high-level <i>ab initio</i> study on the electron affinities of CO₂, OCS, CS₂ and their corresponding anions <inline-formula><tex-math id="M4">\begin{document}$ {\text{CO}}_{2}^{{ - }} $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="10-20231871_M4.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="10-20231871_M4.png"/></alternatives></inline-formula>, OCS^–, <inline-formula><tex-math id="M5">\begin{document}$ {\text{CS}}_{2}^{{ - }} $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="10-20231871_M5.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="10-20231871_M5.png"/></alternatives></inline-formula> by adopting the coupled cluster with singles and doubles (triples) (CCSD(T)), spin-unrestricted open-shell coupled cluster with singles and doubles (triples) (UCCSD(T)), respectively. The equilibrium geometries of the ground states of these molecules are calculated under a series of extended correlation consistent basis sets aug-cc-pV (<i>X</i>+<i>d</i>)Z (<i>X</i> = T, Q, 5) and complete basis set extrapolation (CBS) limit. The effects of core-valence (CV) electron correlation and scalar relativistic (SR) on equilibrium geometry of the ground state are studied, and our results are compared with previous experimental observations and theoretical data. Our calculations are in good agreement with the previous results. It is found that the calculations of equilibrium geometries of these molecules tend to converge. It is noted that the scalar relativistic effect has little influence on the equilibrium structure of the neutral molecule, but it has more significant influence on the bond angle of <inline-formula><tex-math id="M6">\begin{document}$ {\text{CS}}_{2}^{{ - }} $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="10-20231871_M6.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="10-20231871_M6.png"/></alternatives></inline-formula>.With the increase of atomic number, the core-valence correlation effect exerts a more remarkable influence on the equilibrium structures of ground states of CS₂ and <inline-formula><tex-math id="M7">\begin{document}$ {\text{CS}}_{2}^{{ - }} $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="10-20231871_M7.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="10-20231871_M7.png"/></alternatives></inline-formula> molecules except for <i>R</i>_C-S of OCS^–. Based on accurate structures, the adiabatic energy values of neutral molecules CO₂, OCS, CS₂ by CCSD(T) method and those of <inline-formula><tex-math id="M8">\begin{document}$ {\text{CO}}_{2}^{{ - }} $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="10-20231871_M8.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="10-20231871_M8.png"/></alternatives></inline-formula>, OCS^–, <inline-formula><tex-math id="M9">\begin{document}$ {\text{CS}}_{2}^{{ - }} $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="10-20231871_M9.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="10-20231871_M9.png"/></alternatives></inline-formula> by using UCCSD(T) and spin-restricted open-shell coupled cluster with singles and doubles (triples) (RCCSD(T)) are calculated, respectively. And finally, the adiabatic electron affinities (EAs) of the neutral molecules CO₂, OCS, CS₂ are obtained. The effects of different basis sets, CBS, correlation effects and zero-point energy correction on the EA values of these molecules are investigated. It is found that both the scalar relativistic effect and the core-valence correlation effect affect the EAs of neutral molecules, and the core-valence correlation effect has a more significant effect on the EA value. The results show that the correlation effect has more significant influence on the adiabatic EA than the equilibrium structure of the ground state of neutral molecules. Based on the CBS+ΔCV+ΔDK+ΔZPE calculation, accurate EA information is acquired. Our results of EA values are within the experimental error. This work will enrich the information about spectral constants and electron affinities of carbon-containing triatomic molecules, and provide an important reference for experimental spectral analysis.