Computational search for metastable high-spin C5Hn (n = 4, 5, 6) species

Publication date: 15 September 2018Source: Computational and Theoretical Chemistry, Volume 1140Author(s): Maria G. Moreno-Armenta, Harrison Rojak Pearce, Pierre Winter, Andrew L. CooksyAbstractA search for small hydrocarbon radicals with two electronic spin states of comparable stability has identified 9 candidates among singlet and triplet states of various isomers of cyclic C5H4, cyclic C5H6, and acyclic C5H6. No quartet states of C5H5 were found to be comparable in energy to the doublet state of the same structural isomer. Equilibrium geometries, term energies, and vertical excitation energies have been predicted by CCSD(T)-F12a/cc-pVDZ-F12 calculations. Relative coupled cluster energies are in fair agreement with small active space MCSCF calculations, which were then used for rough predictions of the intersystem crossing (ISC) barriers. Results suggest that only 1,3-cyclopentadienylidene, with a calculated barrier of 71 kJ mol−1, is likely to be experimentally observable in both high-spin and low-spin electronic states. The other candidates found to have ISCs in this work have potential energy curves that pose barriers of less than 35 kJ mol−1 for relaxation to the ground state. Surface hopping calculations on the 1,3-cyclopentadienylidene surface have further characterized the dynamics of the ISC for that system.Graphical abstract

Source: Computational and Theoretical Chemistry - July 29, 2018 Category: Chemistry Source Type: research