M. O. Bulanin

On the ethene/HCl Van der Waals complexes observed in liquefied argon and liquefied nitrogen

The mid-infrared (4000–400 cm−1) and far-infrared (300–10 cm−1) spectra of C2H4/HCl mixtures, dissolved in liquefied argon (93–125 K) and in liquefied nitrogen (80–118 K) are discussed. In all spectra, experimental evidence was found for the existence of 1:1 and 1:2 Van der Waals complexes. Using spectra recorded at different temperatures, the complexation enthalpy ΔH° for the 1:1 complex was determined to be −8.7(2) kJ mol−1 in liquid argon and −6.4(4) kJ mol−1 in liquid nitrogen, while for the 1:2 complex a ΔH° of −18.3(6) kJ mol−1 was found. For all species studied, the vibrational frequencies were obtained from ab initio calculations at the MP2/6−311+G** level. Using the SCRF/SCIPCM scheme to correct for the solvent influences, and using statistical thermodynamics to account for the zero-point vibrational and thermal contributions, approximate values for the dissociation energy were calculated from the complexation enthalpies. The resulting values, −12.7(5) kJ mol−1 for the 1:1 complex and −26.9(2) kJ...

Spectroscopic Studies of Diatomics in Dense Non-polar Fluids: an Overview

Abstract In this paper an overview of theoretical and experimental work in spectroscopic, mainly infrared, studies of diatomic molecules in dense nonpolar fluids is presented. Special attention is paid to some unsolved problems encountered in analyses of the band shapes and spectral moments.

Vibration-rotation spectra of HCl in rare-gas liquid mixtures: Molecular dynamics simulations of Q-branch absorption

New experimental results are presented on the fundamental IR band shape of HCl dissolved in neat liquid Ar and Ar doped with Kr and Xe. A strong enhancement of the absorption in the range of a central Q-branch is observed in the spectra of doped solutions. Semiclassical molecular dynamics simulations of the spectral band profile are carried out using (12-6) Lennard-Jones site–site interaction potentials. The parameters of these model potentials were deduced by fitting the available anisotropic interaction surfaces, accurately describing the structure of binary rare-gas-HCl van der Waals complexes. Simulations realistically reproduce the observed triplet band structure and its evolution with changing thermodynamic conditions. The analysis of the influence of anisotropic interactions on the orientational dynamics of solutes and orientation-dependent radial distribution functions reveals the mechanisms that contribute to appearance of the Q-branches. It is shown that long-living solute-solvent spatial correl...

An experimental study of interaction-induced effects in the IR spectra of HI–Xe gas mixtures

Significant interaction-induced perturbation of the dipole moment function for the hydrogen iodide molecule is demonstrated in the absorption spectra of gas mixtures with xenon at elevated pressures. The integrated IR intensity of the (0001) ← (0000) HI fundamental stretch mode is found to increase by about 50% and the intensity of the first vibrational overtone (0002) ← (0000) mode to decrease by an order of magnitude in the spectra of binary Xe:HI van der Waals dimers, compared to the absorption intensities of free HI. Strong m-dependent variation with the perturber gas densities of the spectral line intensities for unbound molecules renders the Herman–Wallis analysis of the vibration–rotation coupling effect on the dipole moment function invalid for the high-density gas systems.

Theoretical study of the spectral and structural parameters of van der Waals complexes of the Li+ cation with the H2, D2, and T2 isotopomers of the hydrogen molecule

The three-dimensional vibrational problem for the isolated binary complexes formed by the Li+ cation with all the isotopomers of the hydrogen molecule is solved by the variational method using sufficiently exact nonempirical adiabatic surfaces of the potential energy and the dipole moment. Information on the largeamplitude vibrations was obtained for the first time, and the anharmonic effects caused by the interaction of the different internal degrees of freedom in these weakly bound van der Waals complexes were consistently taken into account. The frequencies and intensities of many spectral transitions are determined, and the average values of geometrical parameters and the dipole moment are calculated for the ground and excited vibrational states.

Experimental analysis and modified rotor description of the infrared fundamental band of HCl in Ar, Kr, and Xe solutions.

We report an experimental study of the rotovibrational fundamental PQR-band shapes in the IR absorption spectra of HCl dissolved in condensed rare gases in a wide range of temperatures. The effective vibrational frequencies are determined from analysis of the fine rotational structure partially resolved in the band wings. The central Q-branch components appear redshifted with respect to the effective vibrational frequencies, their shifts in different solvents found to match the HCl stretching mode shifts in binary Rg...HCl van der Waals heterodimers. Theoretical quasi-free rotor and modified rotor models are applied to describe evolution of the band profiles at changing thermodynamic conditions. Both models are shown to reproduce equally well the observed spectral density distributions in the band wings. However, the modified rotor formalism that accounts for depopulation of the lower-energy rotational solute states provides better agreement with the experiment in the range of the P- and R-branch maxima. We surmise that the Q branches separated from the measured spectral profiles are formed by transitions between rotationally hindered states of diatomic molecules coupled to the solvent by the local anisotropy of the interaction potential.

First vibrational overtone bandshape of HCl in fluid SF6 : An experimental and theoretical study

The first overtone band profiles are recorded in the IR spectra of the HCl molecular probes diluted in SF6, both below and above the critical point of the solvent. The spectral density distribution is considered as an additive superposition of the contributions due to the quasifree rotating and the rotationally-hindered probes. A recently proposed spectral theory is applied for description of the quasifree contribution. Good agreement is obtained between the experimental and calculated spectral profiles. The vibration–rotation coupling constant for the HCl molecules is found to decrease in high-density fluids. The central Q-branch components associated with the hindered solute states are separated from the measured spectra and their transformation is studied in a broad range of well-controlled thermodynamic conditions. We discuss the possible influence of the interaction-induced dipole transitions on the absorption in the vicinity of the band center.

Dipole moment functions of van der waals complexes of HF and HCl with rare gas atoms

Abstract A simple electrostatic model based on a single-centre multipole expansion is applied to derive the dipole moment functions of complexes formed by the HF (DF) and HCl (DCl) molecules with rare gas atoms. Vibrationally averaged ground state dipole moments agree quite well with the available experimental data. Some transition dipole moments for the internal modes of complexes are also estimated.

Collision-induced shift of the ionization continuum and interaction polarizabilities of rare-gas atoms

Contributions to the incremental pair polarizability traces of Ne, Ar, Kr and Xe due to the shift of the ionization continua are evaluated using the Kramers–Kronig-type integral expression modified to account for the effect of atomic collisions. Interaction trace functions are computed and their shapes explained by the interplay between attractive and repulsive interactions, resulting in the redistribution of the dipole oscillator strength distribution in the continuum. The effect of the spin–orbit coupling on the interaction polarizability is demonstrated. The calculated second dielectric virial coefficients B e are in better agreement with the room-temperature experimental data than the results of other recent studies are. The strong temperature dependence of B e found in experiments remains unexplained, however.

Interferometric determination of the dispersion of vibrational polarizability and the integrated intensities of fundamental bands of 32, 34SF6 and NF3 molecules

The refractivity of gaseous SF6 and NH3 in the region of the intense absorption bands of these compounds was measured by two-beam, two-color interferometry using a He-Ne laser and a CO2 laser tunable throughout its emission lines. Quantitative data on the profiles of the absorption bands of these gases were also obtained by IR Fourier spectroscopy. By using the joint processing of the results of refractometric and spectral measurements on the basis of the Kramers-Krönig formalism, the dispersion dependences of the vibrational polarizabilities of the given molecules were calculated and the integrated intensities of their fundamental vibrational bands were refined. A table of values of total and vibrational polarizabilities at the emission frequencies of the CO2 laser was compiled.