Singlet—triplet gap in HCl halocarbene

Density functional calculations of the influence of substitution on singlet–triplet gaps in carbenes and vinylidenes

“…To carry out these simulations, structures and force constants were calculated at levels of electronic structure theory that would not be expected to be particularly trustworthy, and Gilles et al 39 noted that this could lead to substantial error in the assigned multiplet splittings. The present DFT predictions are in reasonable agreement with the different gradient-corrected DFT prediction of Russo et al 42 (within 0·16 eV) and the empirically In tert-butylvinylidene, the DFT predicted relative energy of the 3 AЈ state is excellent being less than 1 kcal mol…”

“…Our predicted DFT C-I bond length is 0·05 Å shorter than the HF/STO-3G* result of Gilles et al, 39 but the latter level of theory is too low to be regarded as a trustworthy benchmark. Our DFT geometries for HCI agree closely with those calculated by Russo et al 42 using similar levels of DFT. Russo et al 42 noted that the vibrational frequencies predicted at the DFT level were in much better S. E. WORTHINGTON AND C. J. CRAMER agreement with experiment 39 than those derived from the HF/STO-3G* calculations of Gilles et al 39 Hence, the current DFT singlet geometries for HCBr and HCI appear reasonable.…”

“…Agreement is good ( ± 0·01 Å in bond lengths, ± 2Њ in angles), however, between the current predictions and either the MCSCF calculations of Scuseria et al 40 or the DFT calculations of Russo et al 42 Experimental data are unavailable for the substituted vinylidenes. We are unaware of any other calculations on tert-butylvinylidene, for which the structures of the various electronic states are unremarkable.…”

“…[64][65][66] DFT has proven to be an extremely useful tool for other carbenes and isoelectronic systems. 13,17,18,29,33,42,[67][68][69][70][71][72][73][74][75][76] The accuracy of various DFT functionals in the prediction of S-T gaps appears to derive from their ability to account for important non-dynamic correlation effects in the hypovalent systems (that is, the extent to which multiple configurations having the same state symmetry mix into the final state representation; see Figure 1). DFT, by construction, also accounts for dynamic correlation effects in an approximate fashion, and accomplishes all of this within what amounts to a single-determinant formalism.…”

Laser Transient Absorption Spectroscopy of Bromomethylene

“…All simple Spectroscopic studies of halomethylenes can shed light carbenes possess at least three low-lying electronic states on the relative strengths of the different interstate couplings and the observed spectral complexities arise from coupling in CH 2 . Except possibly for the case of HCI (7,8), the and perturbations between energy levels nominally associ-lowest electronic state is singlet in character, X 1 A, and the ated with these different electronic states. For CH 2 , the low-triplet state, corresponding to X 3 B 1 in CH 2 , lies at increasest state is a triplet (X 3 B 1 ), which lies some 3150 cm 01 (5) ingly higher energy the lighter the halogen atom.…”