Anharmonic force field, structure, and thermochemistry of CF2 and CCl2Electronic supplementary information (ESI) available: Force constants and thermochemical properties of CF2 and CCl2. See http://www.rsc.org/suppdata/cp/b2/b202865d/

Abstract

The anharmonic force field up to quartic terms has been calculated for both CF 2 and CCl 2 at the CCSD(T) level of theory with large basis sets. The calculated spectroscopic parameters are in excellent agreement with the available experimental data. The equilibrium structure of CCl 2 has been calculated at the CCSD(T) level of theory with the cc-pV5Z basis set (including core correlation corrections). It is in excellent agreement with the semi-experimental equilibrium structure derived from the experimental rotational constants and the ab initio rovibrational interaction parameters. The heats of formation of CF 2 and CCl 2 have been calculated using the W2 method and are À193.43 and 227.96 kJ mol À1 , respectively.

A Combined Ab Initio/Franck–Condon Study of the ÖX̃ Single‐Vibronic‐Level Emission Spectrum of CCl2 and the Photodetachment Spectrum of CCl2−

“…Considering the computed equilibrium bond lengths, r e (CCl), and bond angles, θ e (ClCCl), for the four electronic states studied, the maximum spreads of the computed r e and θ e values obtained with the three basis sets used here employing the RCCSD(T) or CASSCF/MRCI methods are less than 0.008 Å and 0.29° respectively, which may be considered as the maximum uncertainties associated with the computed geometrical parameters obtained in the present study. For the ${{\rm{\tilde X}}{}^{\rm{1}}{\rm{A}}_{\rm{1}} }$ state of CCl 2 , the averages of the calculated r e and θ e values obtained employing the larger AV5Z and ACVQZ basis sets are 1.7133±0.0019 Å and 109.24±0.06° respectively, which agree very well with available experimental equilibrium values (1.7113±0.0010 Å and 109.22±0.10°)21 and r 0 / θ 0 values (1.714±0.001 Å and 109.35±0.04°;26 see Table 1). Similarly for the ${{\rm{\tilde A}}^{\rm{1}} {\rm{B}}_{\rm{1}} }$ state of CCl 2 , there is good agreement between the computed r e and θ e values (averages of CASSCF/MRCI values using the AVQZ and AV5Z basis sets:1.6539±0.0014 Å and 131.68±0.04°) and the experimental r 0 and θ 0 values (1.652±0.005 Å and 131.4±0.9°) obtained from rotational analysis in the LIF study 7.…”

“…For earlier experimental and/or lower‐level theoretical values, see refs. 20, 21 and 23.) Considering the computed equilibrium bond lengths, r e (CCl), and bond angles, θ e (ClCCl), for the four electronic states studied, the maximum spreads of the computed r e and θ e values obtained with the three basis sets used here employing the RCCSD(T) or CASSCF/MRCI methods are less than 0.008 Å and 0.29° respectively, which may be considered as the maximum uncertainties associated with the computed geometrical parameters obtained in the present study.…”

Multireference Correlation Consistent Composite Approach [MR-ccCA]: Toward Accurate Prediction of the Energetics of Excited and Transition State Chemistry†

“…There has also been significant divergence between the experimental (−3 ± 3 kcal mol −1 ) and theoretical values (−19.5 ± 2 kcal mol −1 ) − for the Δ E S−T of dichloromethylene (CCl 2 ). This may be connected with the fact that CCl 2 is a lot less stable than some other halocarbenes, for example, difluoromethylene (CF 2 ), making it difficult to study using matrix-isolation techniques …”

“…This may be connected with the fact that CCl 2 is a lot less stable than some other halocarbenes, for example, difluoromethylene (CF 2 ), making it difficult to study using matrix-isolation techniques. 98 MR-ccCA-AQCC(S_DT) estimates ∆E S-T for CCl 2 as -19.7 kcal mol -1 , which is in good agreement with the -19.2 kcal mol -1 of a recent theoretical prediction using CASBCC4 method by Shen et al 96 The contribution of the various components of MR-ccCA to the estimated value indicates that a high-level correlated theoretical method is needed to predict quantitative results for halogen-containing compounds. To illustrate, the CASPT2/aug-cc-pVnZ (where the aug-cc-pV(n+d)Z basis set was used for chlorine) CBS limits using S_DT, S_TQ, and P_DTQ extrapolation schemes are -17.2, -17.6, and -17.6 kcal mol -1 , respectively.…”

The Singlet–Triplet Separation in CF2: State‐of‐the‐Art Ab Initio Calculations and Franck–Condon Simulations Including Anharmonicity

“…[c] See original work and also ref. 25. [d] The electron kinetic energy of the origin peak centre; see original work.…”