A priori results for molecular geometry, scaled quantum mechanical (SQM) force field, and vibrational spectra of pyridazine

Infrared spectra of pyrazine, pyrimidine and pyridazine in solid argon

“…The assignments for the region below 1050 cm K1 have also been the motive of some controversy in the past. In consonance with the predictions of Boese and Martin [23], and also with our theoretical calculations, the bands corresponding to modes (19) and (20), of B 2 symmetry, were observed as low-intensity absorptions at 1062.7 and 1045.5 cm K1 , respectively. Note that mode (19) has been repeatedly misassigned in the past to the band due to mode (5), around 1168 cm K1 (as discussed above, mode (5) has been wrongly assigned to a band around 1350 cm K1 , which is due to a combination tone-see Table 4).…”

“…The proposed vibrational assignments were claimed to satisfy the three Teller-Redlich product rules within limitations imposed by evident Fermi resonance perturbation of some of the fundamentals [12]. However, several changes to the assignments made by Stidham and Tucci [12] were later proposed by Jordan and Parmenter [13], Chappel and Ross [14], Ozono et al, [15] Wiberg [16,17], Navarro et al [18] and Bérces et al, [19] some of these supported by results of empirically-based traditional normal mode analysis or low-level ab initio predictions of the vibrational spectra. Higher level theoretical calculations of vibrational spectra of pyridazine (undertaken still within the harmonic approximation) were reported more recently by Billes et al [20,21] and Martin and Alsenoy [22], whereas Boese and Martin [23] and K. Berezin, Nechaev and El'kin [24] reviewed the vibrational assignments for pyridazine taking into consideration results of anharmonic vibrational calculations.…”

Vibrational spectrum of pyridazine

“…The last ring deformation normal modes, and l 9 (A 1 ) l 24 (B 2 ), were assigned at 632 and 663 cm~1, respectively, by Ozono et al 40 on the basis of the B-type contour for the high wavenumber. These results are not in agreement with the calculations of Be rces et al 28 and Jordan and Parmenter,37 which reversed the assignment. In the present work, the bands in the Raman spectrum at 665 and 623 cm~1 were observed, both shown to be depolarized, but with an A-type contour at 665 cm~1 (Fig.…”

“…Past theoretical treatments did not Ðnd sufficient experimental data to clarify this region. 28,30,45,46 In the present work it was possible to resolve the IR band in the liquid phase at 3057 cm~1 into two bands at 3057 and 3068 cm~1 and 3052 and 3067 cm~1 working with and solutions, respectively. This resolution CCl 4 CS 2 could be due to a decrease in the nitrogenÈhydrogen intermolecular interaction when pyridazine is in nonpolar solvents.…”

“…However, sometimes the individual deviations between the calculated and experimental wavenumbers were as much as 76 cm~1. Be rces et al 28 determined an a priori molecular geometry and an a priori SQM harmonic force Ðeld for ground-state pyridazine and checked the vibrational assignments of the and The ab initio HF theoretical pyridazine-h 4 -d 4 . force Ðeld of pyridazine was scaled by scale factors taken over Ðxed from the SQM force Ðeld of benzene9 without any change.…”