Accurate Determination of the Equilibrium and Vibrationally Averaged Structural and Molecular Properties of Difluoromethanimine (F₂CNH) from ab Initio Calculations

Abstract

The availability of large core-valence basis sets together with highly accurate coupled-cluster calculations allow us to present an improved determination of the equilibrium structure of the difluoromethanimine molecule. Core correlation effects and basis set incompleteness have been taken into account to obtain best estimates of the equilibrium geometry. In addition, two important molecular properties, namely, the dipole moment and the nuclear quadrupole coupling constants, have been investigated. The molecular dipole moment has been calculated at the coupled-cluster level using basis sets of different quality, including diffuse functions and taking into account both core correlation effects and basis set incompleteness. The quadrupole coupling constants, evaluated from the electric field gradient at the quadrupolar nuclei, have been computed at the multiconfiguration self-consistent field, Møller-Plesset perturbation to second order, and coupled-cluster levels of theory employing large core-valence basis sets. Because experiment usually determines vibrational ground state molecular parameters, to directly compare theoretical and experimental results a vibrational averaging procedure has been carried out. This allowed us to evaluate the vibrational corrections both for the molecular structure and properties investigated.

Theoretical study of 14N quadrupole coupling constants in some NO-containing complexes: N2O3 and FNO

“…Surprisingly, the cc-pVDZ basis set used in the CASSCF treatment yielded for the EFG tensor components relatively good agreement with experiment, despite the fact that this level of theory produces a poor estimate for geometry in the optimization process. Similar unclear trends in the EFG parameters with the extension of the basis set have been observed by Puzzarini et al [37][38][39].…”

“…In this respect it is interesting that the deviation of the CASSCF(18,15)/d-aug-cc-pVTZ estimate of v cc (À v aa À v bb ) for both nitrogen nuclei with respect to the experimental values amounts to about 0.8%, which is lower than for the CCSD(T)/aug-cc-pVTZ estimate of v cc , acquiring 1.54% and 2.51% at N 1 and N 2 nuclei, respectively. Notice that v cc is the QCC tensor As concerns the effect of the basis sets displayed in Tables 3 and 4, there is little and unclear dependence of the EFG values on increasing the basis set size from cc-pVDZ to d-aug-cc-pVQZ and aug-cc-pCVTZ, including the wCVTZ basis set type recommended for the EFG computations by Puzzarini and Gambi [37]. Comparison with experimental values shows that tendencies of particular tensor components with basis set changes may be different, and improvement of the EFG values for N 1 is often accompanied by deterioration of the values for N 2 .…”

“…The vibrational corrections to the electric properties were ignored in our estimates on grounds that the procedures for their evaluation are highly computer-time consuming, and that the zero-point corrections were found to be negligible for the 14 N quadrupole coupling constants in systems similar to ours [37][38][39]. Geometry optimization and harmonic vibrational frequency calculations were performed using the ''no symmetry" option giving rise to a further increase in the dimensionality of calculations.…”

Submillimeterwave spectrum of CH2PH and equilibrium structures of CH2PH and CH2NH

“…The C@N bond length in CH 2 NH, 1.271 Å , is significantly longer than in the few other molecules for which a reliable equilibrium structure is available: HNCO (1.215 Å ) [47], HNCNH (1.222 Å ) [48], and CF 2 NH (1.239 Å ) [49]. The NH bond length, 1.019 Å , is also longer than in HNCO (1.004 Å ), HNCNH (1.009 Å ) and CF 2 NH (1.013 Å ).…”