Vibronic spectra, ab initio calculations, and structures of conformationally non-rigid molecules of oxalyl halides in the ground and lowest excited electronic states. Part IV: Analysis of the absorption spectra of oxalyl fluoride in the gas phase

Vibronic spectra, ab initio calculations, and structures of conformationally non-rigid molecules of oxalyl halides in the ground and lowest excited electronic states. Part V: Oxalyl chloridefluoride (COCl–COF)

“…However, calculated in such a way (not shown in figure) and experimental bands have significant difference. This result differs from that obtained earlier for transoxalyl chloride [1] and trans-oxalyl fluoride [4], for which calculated and experimental rotational contours of vibronic bands were in good agreement. The possible reason for this is the assumption that the calculation, predicting localization of excitation of oxalyl chloridefluoride molecule on COCl fragment, not exactly evaluates the extent of this localization.…”

“…Similar situation was observed for the trans conformers of the related molecules of oxalyl chloride [1,2] and oxalyl fluoride [3,4]. Since the assignments of m 0 1 (C=O str), m 0 2 (C=O str), and m 0 4 (C-C str) give rise to no doubts, it could be concluded that the CASPT2(8-6)/ccpVTZ method (at least with this basis and active space) poorly predicts these frequencies.…”

“…In spite of the low symmetry, the orbital character in the singlet states (Ã 1 A 00 andB 1 A 00 ) is similar to that in molecules with equivalent CXO fragments (COCl) 2 and (COF) 2 [2,3] and approximately correspond to symmetric and antisymmetric combinations of bonding and antibonding p C=O and non-bonding n O orbitals localized on different fragments. The analyses of the vibronic absorption spectra of (COX) 2 (X = H, F, Cl, Br) [1,4,[32][33][34][35][36][37] established the equivalence of CXO fragments for the trans conformers, at least in the first excited singlet and triplet electronic states. For COCl-COF molecule, the excitation can be localized on one of the carbonyl fragments due to lower symmetry.…”

“…x i Int Dx i Assignments transition was found to be shifted to the blue by about 6000 cm -1 relative to the transition of the trans conformer [4]. For oxalyl chloride molecule, it can be explained by the fact that the minima of the ground (gauche) and excited (cis) states are significantly shifted along the internal rotation coordinate [2].…”

“…1 The first four parts are devoted to the experimental and theoretical investigations of oxalyl chloride (COCl-COCl) [1,2] and oxalyl fluoride (COF-COF) [3,4].…”