Rovibrational analysis of c-SiC2H2: Further evidence for out-of-plane bending issues in correlated methods

Ryan C Fortenberry; Carlie M Novak; Timothy J Lee

doi:10.1063/1.5043166

Rovibrational analysis of c-SiC₂H₂: Further evidence for out-of-plane bending issues in correlated methods

J Chem Phys. 2018 Jul 14;149(2):024303. doi: 10.1063/1.5043166.

Authors

Ryan C Fortenberry¹, Carlie M Novak², Timothy J Lee³

Affiliations

¹ Department of Chemistry and Biochemistry, University of Mississippi, University, Oxford, Mississippi 38677, USA.
² Department of Chemistry and Biochemistry, Georgia Southern University, Statesboro, Georgia 30460, USA.
³ NASA Ames Research Center, MS 245-3 Moffett Field, California 94035 USA.

PMID: 30007394
DOI: 10.1063/1.5043166

Abstract

While the issue of properly describing the out-of-plane bends (OPBs) in sp² hybridized carbon atoms has reappeared for c-SiC₂H₂, the present quantum chemical study provides a new characterization of this molecule in order to aid in its potential detection in astrophysically relevant studies. Combining the previous, high-level approach with MP2-F12/aug-cc-pVDZ gives exceptionally accurate results for the comparison of experimental rotational constants and seemingly reliable vibrational frequencies. Most notably, the brightest fundamental vibrational frequency in c-SiC₂H₂, the b₁ OPB, is predicted to lie at 673.4 cm^-1, within 4.0 cm^-1 of the previous matrix isolation experiment. As with c-C₃H₂, CCSD(T)-F12/aug-cc-pVTZ appears to be quite susceptible to over estimating the OPB anharmonic correction in c-SiC₂H₂ and may also do such for in-plane bends, as well. MP2-F12/aug-cc-pVDZ is less susceptible to these errors, and increasing the step size reduces this positive anharmonicity issue in both the cases. The OPB underestimation, however, likely still remains. Finally, estimates for some anharmonic vibrational frequencies are provided for the methylated form, c-SiC₂HCH₃, which is likely also a product of gas phase reactions of ·SiH with various alkynes.