biostudies-literatureUnknown126(14)DeVine JAAlexander von Humboldt-StiftungMax-Planck-GesellschaftFourier transform infrared spectroscopy of laser-irradiated cryogenic crystals shows that vibrational excitation of CO leads to the production of equal amounts of CO<sub>2</sub> and C<sub>3</sub>O<sub>2</sub>. The reaction mechanism is explored using electronic structure calculations, demonstrating that the lowest-energy pathway involves a spin-forbidden reaction of (CO)<sub>2</sub> yielding C(<sup>3</sup>P) + CO<sub>2</sub>. C(<sup>3</sup>P) then undergoes barrierless recombination with two other CO molecules forming C<sub>3</sub>O<sub>2</sub>. Calculated intersystem crossing rates support the spin-forbidden mechanism, showing subpicosecond spin-flipping time scales for a (CO)<sub>2</sub> geometry that is energetically consistent with states accessed through vibrational energy pooling. ThThe journal of physical chemistry. A2270-2277https://www.ebi.ac.uk/biostudies/studies/S-EPMC9014413biostudies-literatureSpin-Forbidden Carbon-Carbon Bond Formation in Vibrationally Excited α-CO.PMC9014413DeVine JASchwarzer DLau JAChoudhury AWodtke AMfalseSpin-Forbidden Carbon-Carbon Bond Formation in Vibrationally Excited α-CO.Fourier transform infrared spectroscopy of laser-irradiated cryogenic crystals shows that vibrational excitation of CO leads to the production of equal amounts of CO<sub>2</sub> and C<sub>3</sub>O<sub>2</sub>. The reaction mechanism is explored using electronic structure calculations, demonstrating that the lowest-energy pathway involves a spin-forbidden reaction of (CO)<sub>2</sub> yielding C(<sup>3</sup>P) + CO<sub>2</sub>. C(<sup>3</sup>P) then undergoes barrierless recombination with two other CO molecules forming C<sub>3</sub>O<sub>2</sub>. Calculated intersystem crossing rates support the spin-forbidden mechanism, showing subpicosecond spin-flipping time scales for a (CO)<sub>2</sub> geometry that is energetically consistent with states accessed through vibrational energy pooling. Th2022-01-01T00:00:00Z2022 Apr2025-04-19T17:36:47.179Z2025-02-19T03:18:33.656ZS-EPMC90144133538044110.1021/acs.jpca.2c01168