D. N. Shchepkin

Infrared matrix isolation spectra of SF6 dimers

Abstract The infrared spectra of 32 SF 6 , 33 SF 6 and 34 SF 6 dimers were studied in argon and nitrogen matrices. The spectra of SF 6 dimers of like and unlike isotopomers were also calculated taking into account the resonance dipole–dipole and dipole-induced dipole interactions between two triply degenerate oscillators. Two absorption bands with site structure are observed for ( 32 SF 6 ) 2 , ( 33 SF 6 ) 2 and ( 34 SF 6 ) 2 in argon; the ν X , Y band is blue shifted and the ν Z band is red shifted from the ν 3 SF 6 band in accordance with calculated spectra. Three and two components of the predicted quadruplets are identified for 32 SF 6 – 34 SF 6 , 32 SF 6 – 33 SF 6 , respectively. In the spectra of (SF 6 ) 2 in nitrogen matrices the splitting of ν X , Y component of the resonance doublet was observed.

Absorption spectrum of the (CF4) dimer in liquid argon solution

The concentration dependence of the shape of absorption bands in the spectrum of CF4 in liquid argon is studied in the concentration range (0.01–17)×10−3 molar fractions at 93 K. In all spectral regions related to ν3, the shape of the spectral function is determined, along with the Fermi resonance 〈νi,ν3+1,ν4|≈〈νi,ν3,ν 4+2|, by the resonance dipole-dipole interaction. In the spectral region of the Fermi doublet ν 1+ν3≈ ν1+2ν4, the spectrum of the contact (CF4)2 dimer is identified. Agreement between this spectrum and the calculated spectrum is achieved by simultaneously taking intramolecular and intermolecular resonances into account. The distance RC-C in the dimer is 4.85(15) Å. The calculations of the spectra of (12CF4)2 and (13CF4−12CF4) dimers with this value of RC-C in the region ν 3≈2ν4 agree with the experiment.

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.

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.

Integral Intensities of Absorption Bands of Silicon Tetrafluoride in the Gas Phase and Cryogenic Solutions: Experiment and Calculation

The spectral characteristics of the SiF4 molecule in the range 3100–700 cm−1, including the absorption range of the band ν3, are studied in the gas phase at P = 0.4–7 bar and in solutions in liquefied Ar and Kr. In the cryogenic solutions, the relative intensities of the vibrational bands, including the bands of the isotopically substituted molecules, are determined. The absorption coefficients of the combination bands 2ν3, ν3 + ν1, ν3 + ν4, and 3ν4 are measured in the solution in Kr. In the gas phase of the one-component system at an elevated pressure of SiF4, the integrated absorption coefficient of the absorption band ν3 of the 28SiF4 molecule was measured to be A(ν3) = 700 ± 30 km/mol. Within the limits of experimental error, this absorption coefficient is consistent with estimates obtained from independent measurements and virtually coincides with the coefficient A(ν3) = 691 km/mol calculated in this study by the quantum-chemical method MP2(full) with the basis set cc-pVQZ.

Anharmonicity of the XH bond. Changes on H-bond formation☆

Abstract Presently available experimental data on changes in the anharmonicity constant x 11 of the XH bond upon formation of a H-bonded complex are considered. The observed dependence of x 11 on the relative frequency shift Δν/ν is shown to result from contributions of different modulation mechanisms by low-frequency intermolecular vibrations. Within the uncertainty of approximations used in determining these contributions, the anharmonicity is shown to be constant.

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.

Effects of pair resonant dipole-dipole interactions on the formation of band profiles in infrared absorption spectra

Resonant dipole-dipole interactions are shown to play a crucial role in forming the profiles of several bands in the fundamental and overtone regions of the vibrational spectrum for molecules with a relatively large first derivative of the dipole moment (P′>0.3 D). Analytic expressions are derived for the probability density of the matrix element for the interaction of one-and two-dimensional oscillators. We computed the band profiles in the infrared absorption spectrum for a pair of molecules at a fixed distance R ∼ 5 Å, typical of condensed media. Comparison is made with experimental data for low-temperature condensed systems: matrices and solutions in liquefied gases.

The vibrational spectrum of the OCS molecule based on the data on spectra of liquid and cryosolutions

The IR absorption spectra of liquid OCS (T = 135(1) K) and of the following solutions—OCS + Ar (T = 90 K), OCS + N2 (T = 90 K), OCS + Kr (T = 130 K), and OCS + Xe (T = 163 K)—are measured in the range 800–7000 cm−1. From 16 to 40 bands corresponding to transitions to vibrational states up to the third order inclusive are interpreted for basic isotope modification and for the isotopically substituted molecules 18O12C32S, 16O13C32S, and 16O12C34S. In the spectra of the liquids, the spectral moments M(1) and M(2) of all the observed bands are determined. The harmonic frequencies ωi and the anharmonicity constants xik are calculated for all the systems, including the liquid. The anharmonicity is found to be constant within the experimental error. A large shift Δω3 is primarily determined by the dipole-induced dipole interaction.