Quantum chemical characterization of the \({\tilde{X}}(^{1} A_{1} )\), \({\tilde{a}}(^{3} B_{1} )\), \({\tilde{A}}(^{1} B_{1} )\) and \({\tilde{B}}(2{}^{1}A_{1} )\) states of diiodomethylene and the enthalpies of formation of diiodomethylene, iodomethylene and iodomethylidyne

  • George B. BacskayEmail author
Regular Article
Part of the following topical collections:
  1. Shavitt Memorial Festschrift Collection


The equilibrium energies of the \(\tilde{X}(^{1} A{\kern 1pt}_{1} )\), \(\tilde{a}(^{3} B{\kern 1pt}_{1} )\), \(\tilde{A}(^{1} B{\kern 1pt}_{1} )\) and \(\tilde{B}(2{}^{1}A{\kern 1pt}_{1} )\) states of diiodomethylene (CI2) and its atomization and dissociation energies in the complete basis limit were determined by extrapolating valence correlated (R/U)CCSD(T) and Davidson corrected multi-reference configuration interaction energies calculated with the aug–cc–pVxZ (x = T, Q, 5) basis sets and the ECP28MDF pseudopotential of iodine plus corrections for core and core-valence correlation, scalar relativity, spin–orbit coupling and zero-point energies. The geometries and vibrational frequencies were obtained at the CCSD and complete active space second-order perturbation theory levels of theory with the cc–pVTZ basis. Spin–orbit energies were computed in a large basis of configurations chosen so as to accurately describe dissociation to the 3 P and 2 P states of C and I, respectively. These computations were extended to iodomethylene (CHI) and iodomethylidyne (CI), resulting in small corrections to the thermochemistry and the singlet–triplet gap of CHI computed previously. The onset (T 00) of the \(\tilde{A} \leftarrow \tilde{X}\) excitations in CI2 is predicted to be 12,680 cm−1. The Renner–Teller intersection is computed to have a substantially lower energy (6.5 kcal mol−1) than the dissociation barrier on the \(\tilde{A}\) surface, thus internal relaxation via Renner–Teller coupling is expected to be the dominant photochemical channel. The predicted enthalpies of formation of CI2, CHI and CI in their ground states at 0 K are 109.1 ± 1, 102.8 ± 1 and 132.9 ± 1 kcal mol−1, respectively. The computed singlet–triplet gaps in CI2 and CHI are 11.1 and 4.4 kcal mol−1, respectively.


Iodocarbene Enthalpy of formation MRCI Singlet–triplet splitting Renner–Teller effect Electronic excitation 



I wish to express my thanks to the National Computational Infrastructure (NCI) National Facility and Intersect Australia Ltd for their generous allocation of computer time.


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© Springer-Verlag Berlin Heidelberg 2014

Authors and Affiliations

  1. 1.School of ChemistryThe University of SydneySydneyAustralia

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