| Popis: |
The thermochemistry of triacetylene, C 6 H 2 , the corresponding neutral triacetylide radical, C 6 H . , and the triacetylide anion, C 6 H − , has been evaluated by combining mass spectrometric means with high-level ab initio MO calculations at the CCSD(T) level. Experimentally, the ion/molecule bracketing method has been applied to determine the gas phase acidity (Δ G acid ) of C 6 H 2 as 347 ± 3 kcal mol . For this purpose, C 6 H − anions were reacted with various bases for which Δ G acid is known. The computations lead to a dissociation energy of 126.8 ± 1.6 kcal mol for a C-H bond of triacetylene and an electron affinity of 3.69 ± 0.05 eV for the triacetylide radical C 6 H . . Combining the calculated figures in terms of a thermochemical cycle leads to a theoretical prediction of Δ G acid (298 K) = 346.7 ± 2.8 kcal mol ; this is in excellent agreement with the experimental value. The implications of the present results for interstellar chemistry are discussed. |
