Spectroscopic characterization of the complex of vinyl radical and carbon dioxide: Matrix isolation and ab initio study

Abstract

We report on the preparation and vibrational characterization of the CH⋯CO complex, the first example of a stable intermolecular complex involving vinyl radicals. This complex was prepared in Ar and Kr matrices using UV photolysis of propiolic acid (HCOOH) and subsequent thermal mobilization of H atoms. This preparation procedure provides vinyl radicals formed exclusively as a complex with CO, without the presence of either CO or CH monomers. The absorption bands corresponding to the ν(CH), ν(CH), ν(CH), ν(CO), and ν(CO) modes of the CH⋯CO complex were detected experimentally. The calculations at the UCCSD(T)/L2a level of theory predict two structures of the CH⋯CO complex with C and C symmetries and interaction energies of -1.92 and -5.19 kJ mol. The harmonic vibrational frequencies of these structures were calculated at the same level of theory. The structural assignment of the experimental species is not straightforward because of rather small complexation-induced shifts and matrix-site splitting of the bands (for both complex and monomers). We conclude that the C structure is the most probable candidate for the experimental CH⋯CO complex based on the significant splitting of the bending vibration of CO and on the energetic and structural considerations.

Atomic basis functions for molecular electronic structure calculations

“…The atomic basis sets are now made available 93 that allow quantitative calculations of the structure and energetics of typical molecular systems. We are somewhat sorry for our belated report, for they have already been, and are being, used by our colleagues in their studies of unusual molecules under the unusual conditions of lowtemperature high-energy chemistry [94][95][96][97][98][99][100] .…”

Matrix Isolation and Ab Initio Study on the CHF3···CO Complex

“…The augmented valence correlation consistent with basis sets of type L2a_3 was used . This type of basis sets has been successfully used in the previous studies of intermolecular complexes. ,, The L2a_3 basis set is analogous to the aug-cc-pVTZ basis set, but it includes a larger number of primitive Gaussian functions [see the Supporting Information (SI) for details]. Using the optimized geometry, we calculated harmonic vibrational frequencies, and IR intensities at the same level of theory.…”