Extension of a regularizing algorithm for the determination of equilibrium geometry and force field of free molecules from joint use of electron diffraction, molecular spectroscopy and ab initio data on systems with large-amplitude oscillatory motion

IR spectra of nitrobenzene and nitrobenzene-15N in the gas phase, ab initio analysis of vibrational spectra and reliable force fields of nitrobenzene and 1,3,5-trinitrobenzene. Investigation of equilibrium geometry and internal rotation in these simplest aromatic nitro compounds with one and three rotors by means of electron diffraction, spectroscopic, and quantum chemistry data

“…General molecular model is applicable to both spectroscopic and structural studies making possible their joint treatment. This approach presupposing analysis of the molecular Hamiltonian and adiabatic separation of different molecular degrees of freedom was initially developed for semirigid molecular systems with SAM and later extended to nonrigid polyatomic molecules with one or more coordinates of LAM [51][52][53][54][55][56]. The basic idea of subdividing molecular translations, rotations, and vibrations is supplemented with rigorous adiabatic separation of the LAM coordinates.…”

“…[73,74]. Structural analysis of the GED data jointly with the spectroscopic experimental data and quantum chemical calculation results has been performed with the SYMM/DISP/ELDIFF/LARGE software package [51][52][53][54][55][56], whose molecular model is based entirely on the parameters of the PES and advantage of which in the investigation of structure of flexible molecules is briefly characterized above. The necessary ab initio calculations, including the calculation of quadratic and cubic force constants, have been performed by the MP2(full) method using the aug-cc-pVTZ and ccpVTZ basis sets.…”

“…The barrier height value in kcal/mol is given in braces, DZPE is the difference of zero-point vibrational energies for equilibrium and transition states f The proposed estimate Formulation of general problem on GED analysis for nonrigid molecules using potential procedure Within the framework of the potential procedure [49,50], general formulation of the problem of GED data analysis for molecules with one or more LAM coordinates as well as the resulting equations and methods of their solution were presented in Refs. [51][52][53][54][55][56]. Here, we give a brief description of the approach and its main distinctions for the case of symmetric internal coordinates of LAM.…”

“…The c factor can be obtained [50,52] from the condition of the U VSp residual functional minimum for the vibrational spectroscopy (VSp) data: where v k th (c) = v k [R,V] (c) are theoretical vibration frequencies, which correspond to the V scaled (q) = cV(q) scaled potential and depend on the given R geometry as parameters; v k exp are M experimental frequencies of transitions between LAM energy levels; and p k = 1/r k 2 is the weight of the k-th frequency expressed in terms of the r k experimental error. Proceeding from the solution of the stationary Schrodinger equation with calculated V(q) potential in the Hamiltonian (4), the following equation for evaluating this factor has been suggested on the basis of the quantum mechanical first-order perturbation theory [77]:…”

“…So the theoretical B 0 (k) values for the equilibrium configuration, which are, as in the case of B e (k) equilibrium parameters, calculated according to the procedures outlined in Ref. [52], and the averaged \B 0 (k)…”