S.M. Melikova

Unusual spectroscopic properties of CF3H dissolved in liquified Ar, N2, CO, and CO2

Abstract The FTIR spectra of CF 3 H have been studied in liquefied Ar, N 2 , CO, and CO 2 . The effect of a blue shift of frequency of the C – H stretching vibration accompanied by a decrease in the integral intensity of the corresponding ν 1 band was found in the studied series of solvents. The combination bands ascribed to simultaneous excitation of vibrations of interacted molecular partners have been revealed in CO and CO 2 solutions. DFT/B3LYP and ab initio MP2 calculations utilizing the 6-311++G(3df,3pd) basis set suggest weak linear F 3 CH⋯ B complex formation, reproduce the experimentally observed unusual trends for B= Ar , N 2 , CO, CO 2 , and predict the conventional red frequency shift of the ν 1 band for B =NH 3 .

Spectroscopic and structural consequences of intramolecular hydrogen bond formation in ortho-dimethylaminomethylphenol

Abstract Ab initio and density functional calculations are applied to analyse the structure of the Mannich base ortho -dimethylaminomethylphenol with emphasis on a detailed description of the properties of the intramolecular hydrogen bond. The calculated structures of the components, phenol and dimethylbenzylamine, are compared to the geometries of the hydrogen-bonded and open forms of the Mannich base. Additionally, the gas-phase infrared spectra of the Mannich base and of dimethylbenzylamine are presented. The experimental spectra are confronted with theoretical infrared spectra and interpreted with the aid of a detailed normal coordinate analysis. Trends in the modifications of computed harmonic force constants upon closure of the intramolecular hydrogen bond are monitored and discussed.

Influence of hydrogen bonding on the conformation of ortho-aminomethylphenol

Abstract Intramolecular hydrogen bonding in ortho -aminomethylphenol is analysed with the aid of ab initio and density functional theory calculations. Selected properties of the components, phenol and benzylamine, are compared to those of the hydrogen-bonded form of the Mannich base as well as that of the non-hydrogen-bonded structure. Additionally, the gas phase infrared spectrum of benzylamine is analysed in terms of the possible conformations of the molecule.

Effect of electrical and mechanical anharmonicity on vibrational spectra of H-bonded complexes: phenoltctdot;B (B = acetonitrile, pyridine) systems

Abstract The model of the anharmonic dipole moment function of the H-bonded complex AHtctdot;B is applied to C6H5OH(D) complexes with acetonitrile and pyridine. The frequencies and absolute intensities data for the overtones and the fundamental absorption bands in a wide spectral region (50–8000 cm−1) and derivatives of the dipole moment function are presented and compared with ab initio calculation results on the DFT B 3 LYP 6–31 G ∗∗ level.

Infrared studies of weak B…HCl (B = HCl, CO, Xe, N2) complex formation in solid Kr solutions

Abstract IR spectra of small B…HCl (B = HCl, N 2 , Xe, CO) complexes have been studied in solid phase at equilibrium conditions by using the technique of crystal growth from a liquid Kr solution. Triplet to doublet structure evolution of the ν(HCl) fundamental band has been revealed at liquid to crystal state transition of the noble (Xe, Kr) gas solutions. Residual rotational structure observed at wings of the ν(HCl) band and spectral moments analysis suggest that noncomplexed HCl molecules continue to rotate in solid solutions studied. Self-association of HCl molecules has been found in solid Kr, while this process was strongly suppressed in solid Xe. Spectral parameters of the ν c fundamental bands and enthalpy of formation ΔH were estimated for B…HCl complexes in solid Kr. Comparative analysis of the ν c (CO) and ν c (HCl) bands shows that the ν c (HCl) bands is perturbed due to intermolecular H-bonding and the OC…HCl complex does not rotate in solid Kr. Relative changes of the integral intensity A of the fundamental ν c (HCl) and ν c (CO) bands due complex formation have been derived from the temperature dependence of the A value.

The model analysis of the effects of electrical and mechanical anharmonicity on vibrational spectra of H-bonded complexes

The model of anharmonic dipole moment function is applied for the analysis of the hydrogen bridge XH· ··Y vibrations. The model allows to predict the characteristic features of the hydrogen bond formation in the intensities of n(XH) and n(XY) transitions. Three complexes of phenol with different proton acceptors (acetonitrile, pyridine and trimethylamine) are chosen as model systems. The experimental data and the model calculations are compared with the Density Functional Theory calculations at B3LYP/6-31G pp level. q 2000 Elsevier Science B.V. All rights reserved.

Higher-order transitions in the IR spectrum of the weak OC⋯HCl complex dissolved in liquid CO

Abstract Infrared spectra of HCl-doped CO solutions have been studied at T ∼140–90 K. First overtone and combination bands of the OC⋯HCl complex were revealed at the lowest temperature of the liquid solution. Ab initio calculations utilizing the 6-311++G(3df,3pd) basis set with electron correlation at the n th-order Moller–Plesset (MPn, n ⩽4) levels of approximation predict minima for the CO⋯HCl and OC⋯HCl linear structures. Based on simplified treatment of anharmonic interactions between CO and HCl constituents, the model estimations of the dipole transition moments have been performed.

Temperature dependence studies and model calculations of ν(OH) and ν(OD) band shapes of salicylaldehyde

Abstract IR spectra of salicylaldehyde (OH and OD) have been studied over a wide temperature range in teh vapor phase, liquid Xe solution and Ar matrices. Far IR and Raman spectra have been obtained. Ab initio calculations at the 3-21G∗∗ level have been performed in order to establish the geometry of the molecule, normal coordinates and frequencies of vibrations. It has been found that profiles of both ν (OH) and ν (OD) bands are formed by the fundamental transition ν s , by the weak sum transition ν s + ν 3 , where ν 3 = 264 cm −1 is an in-plane vibration involving deformation of the chelate ring with significant stretching of the intramolecular H-bond, and by a series of hot transitions from levels of ν 3 and other low frequency modes ( ν i ) of the chelate ring. The ν (OH) profile is perturbed additionally by several Fermi resonances with overtones and combinations of bending vibrations δ(OH). Anharmonicity constants, which characterize coupling of ν s with ν i and δ(OH), have been derived from the temperature dependence of the first spectral moments of the bands, using the results of the 3-21G∗∗ treatment. Model calculations of ν (OH) and ν (OD) band shapes have been performed.

Vibrational spectra of OC⋯HCl complex in Kr solutions at liquid to solid phase transition

Abstract Fundamental and first overtone bands of HCl, CO molecules and OC⋯HCl complex were studied in liquid and solid Kr solution near the phase transition. Triplet to doublet shape transformations were observed for both fundamental ν (HCl) and first overtone 2 ν (HCl) bands at liquid to crystal state transition. Self-association processes of HCl in Kr solutions have resulted in the registration of two to several new sharp peaks on the low frequency P branch of the ν (HCl) band, whereas they only gave an additional diffuse absorption on the P branch of the 2 ν (HCl) band. Evolution of the ν (CO) and 2 ν (CO) bands, observed at temperature lowering of liquid Kr solution, has shown an increased restriction of the rotational motion of CO in an orienting field of the nearest neighbors. Triplet to singlet shape transformation was found for both the CO bands at liquid to crystal state transition. Asymmetry of the central parts of the bands and high frequency shoulder, which are increased at temperature lowering of the solids, suggest the consecutive transformation of orientational motion of CO into libration and growth of vibrational–translational coupling in CO doped low temperature Kr crystal. OC⋯HCl complex formation with a weak intermolecular H-bond were studied by observation of the red shifted ν c (HCl) band and of the blue shifted ν c (CO) and 2 ν c (CO) sharp bands in the solid state. Spectral parameters of dimer bands were estimated.

Effect of liquid to solid phase transition on rotational and vibrational broadening of vibrational bands of CF3CL in Xe solutions

Abstract Fundamental and second order bands of CF 3 Cl dissolved in Xe solutions have been studied near the melting point by using technique of transparent solid sample growth from the liquid rare gas solution. The widths at half maximum 2 Γ of the bands were noticeably decreased after crystallization, especially in the case of the broadest 2 ν 4 ( E ) band. Experimental data have been interpreted in the framework of Debye limit (〈 ω 〉 τ J ≪1) for the J -model of a heavy symmetrical top rotation. Additional broadening, caused by fluctuational mechanisms of vibrational relaxation, was taken into account. Angular momentum correlation times ( τ J ⊥ and τ J ∥ ) and parts of widths, originated from vibrational relaxation, were estimated for the liquid and solid Xe solutions near the melting point. The results obtained have shown decreasing effect of fluctuational broadening and increasing disturbance of rotational motion of CF 3 Cl when going from the liquid Xe solution to the crystal state.