ABSTRACT
The FTIR spectra of fluoroform trapped in argon and nitrogen matrixes are studied at T â¼ 10-30 K. The bands of E symmetry show the splitting effect in a nitrogen matrix, which is absent in an argon matrix. The effect is the most prominent in the case of the ν4 CH bending vibration. It decreases slightly with increasing temperature. Both static and Car-Parrinello molecular dynamic simulations suggest that the degeneracy lifting is due to C3v symmetry lowering caused by interactions between fluoroform and all neighbor N2 matrix molecules.
ABSTRACT
The FTIR spectra of F(2)ClCH and Cl(3)CH(D) in mixtures with trimethylamine (TMA) have been studied in liquefied Kr in approximately 800-4000 cm(-1) frequency range. Spectroscopic evidence of a medium strength H-bond formation with conventional features has been found between these weak CH "proton donors" and TMA. The relative stability of the complexes has been determined in a series of temperature (T = 118-157 K) measurements of integrated intensities of vibrational bands ascribed to monomer and complex species. The complexes found are characterized by the red shift of the nu(1)(CH) stretching vibration of the haloforms studied. In the case of chloroform, the substantial red shift is accompanied by a noticeable broadening effect and by a marked growth of the intensity of this band. The spectroscopic changes caused by the complex formation have been also registered for vibrations of TMA. Specifically, the bands situated in the frequency domain of CH stretching vibrations of TMA show a weak blue shift, whereas the NC stretching vibrations are red-shifted. Ab initio MP2/6-311++G(2d,2p) a priori counterpoise corrected calculations, made for a series of haloforms and TMA, reproduce the main spectroscopic observations. The results obtained also suggest that the vibrational mode coupling between vicinal C-H and C-B (B = Hal, N) bonds is to a great extent responsible for the sign of these bond length changes and for the sign of the frequency shifts of the respective stretching vibrations upon complex formation.
ABSTRACT
The features of blue- and red-shifted electron acceptor-donor (ACH/B) hydrogen bonds have been compared by using quantum chemical calculations. The geometry, the interaction energy and the vibrational frequencies of both blue- (ACH=F3CH, Cl3CH with B=FCD3) and red-shifted (ACH=F3CH, Cl3CH with B=NH3 and ACH=CH3CCH with B=FCD3, NH3) complexes were obtained by using ab initio MP2(Full)/6-31+G(d,p) calculations with the a priori basis-set superposition error (BSSE) correction method. One-dimensional potential energy and dipole moment functions of the dimensionless normal coordinate Q1, corresponding to the CH stretching mode of ACH, have been compared for both types of complexes. Contributions of separate components of the interaction energy to the frequency shift and the effect of electron charge transfer were examined for a set of intermolecular distances by using the symmetry-adapted perturbation theory (SAPT) approach and natural bond orbitals (NBO) population analysis.
ABSTRACT
Mid-infrared spectra of mixed solutions in liquid xenon containing fluoroform and either ammonia or pyridine have been investigated at temperatures between 173 and 213 K. For both Lewis bases, a new band is found in the CH stretching region at a frequency approximately 5 cm(-1) higher than that of monomer fluoroform, which is assigned to a complex between fluoroform and the Lewis base. A detailed analysis of the nu1/2nu(4) Fermi resonance in the proton donor shows that the blue shifts observed for the complexes are not caused by a strengthening of the CH bond during the complexation, but are due to the changes in the Fermi resonance interactions. Information on the nu1/2nu(4) Fermi resonance was also obtained for the complexes of fluoroform with dimethyl ether and trimethyl amine.
