Ruslan E. Asfin

Degeneracy Lifting Effect in the FTIR Spectrum of Fluoroform Trapped in a Nitrogen Matrix. An Experimental and Car-Parrinello Molecular Dynamics Study.

The FTIR spectra of fluoroform trapped in argon and nitrogen matrixes are studied at T ∼ 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.

Communication: Evidence of stable van der Waals CO2 clusters relevant to Venus atmosphere conditions

Non-intrusive spectroscopic probing of weakly bound van der Waals complexes forming in gaseous carbon dioxide is generally performed at low pressures, for instance in supersonic jets, where the low temperature favors dimers, or in few-atmosphere samples, where the signature of dimers varying as the squared gas density is entangled with the dominating collision-induced absorption. We report experimental and theoretical results on CO2 dimers at very high pressures approaching the liquid phase. We observe that the shape of the CO2-dimer bands undergoes a distinctive line-mixing transformation, which reveals an unexpected stability of the dimers despite the collisions with the surrounding particles and negates the common belief that CO2 dimers are short-lived complexes. Our results furnish a deeper insight allowing a better modeling of CO2-rich atmospheres and provide also a new spectroscopic tool for studying the robustness of molecular clusters.

Determination of Strong Absorption Band Profiles of Low-Temperature Liquids from Reflection Spectra: The ν3 Band of Liquefied Tetrafluoromethane (CF4).

An experimental unit for recording the combined reflection-absorption spectra of low-temperature liquids was designed and manufactured and an algorithm for obtaining the extinction coefficient was developed. The manufactured experimental unit and the algorithm were tested by recording, for the first time, the absorption spectrum of liquefied CF4. The band parameters derived from the experimental data are compared with estimates available in the literature.

Infrared Studies of the Symmetry Changes of the 28SiH4 Molecule in Low-Temperature Matrices. Fundamental, Combination and Overtone Transitions

Infrared spectra of 28SiH4 in argon and nitrogen matrixes at low temperature 6.5-20 K in the region of overtone and combination transitions were recorded for the first time. Additionally, the high-resolution spectra were obtained in the fundamental region. The frequencies and the relative intensities of all bands were determined. The set of experimental data suggests that the symmetry of molecules studied in the matrixes is different from the symmetry of the free molecules because of an interaction with the environment. The symmetry of 28SiH4 changes from Td to C3v on transition from the gas phase to a nitrogen matrix and to D2d on transition to an argon matrix. A modeling of SiH4 molecule force fields explains the experimental data as a change of a force constant of the selected SiH bond in the case of SiH4 in the nitrogen matrix or force constants of two opposite angles in the case of SiH4 in the argon matrix. In spite of small values of these changes, they result in noticeable spectroscopic effects: the band splitting and appearance of new bands in matrix spectra compared with spectra of free SiH4. The interpretation of transitions in the fundamental and combination regions was performed.

The infrared study of fluoroform + methyl fluoride mixtures in argon and nitrogen matrices. Evidence of nonlinear blue-shifting complex formation

The FTIR spectra of fluoroform + methyl fluoride mixtures trapped in argon and nitrogen matrices are studied at T~10-30 K. Spectroscopic changes observed in the region of the CH stretching mode of fluoroform are typical for weak blue shifting H - bonds of CH⋯F type. The degeneracy lifting effect found on E - type bands of fluoroform interacted with methyl fluoride suggests the complex formation of a nonlinear form. The experimental results are confirmed by ab initio calculations of fluoroform + methyl fluoride based on the second order Møller-Plesset theory of perturbations utilizing advanced basis set. Nonlinear complexes are stabilized by the basic CH⋯F interaction and additionally by van der Waals-type CD⋯FC contacts between deuterated methyl fluoride and fluoroform.

He-broadening and shifting coefficients of HCl lines in the (1←0) and (2←0) infrared transitions

ABSTRACT We report experimental results on the broadening and shifting coefficients in a large interval of J quantum numbers in the fundamental and first overtone vibration–rotation bands of the HCl molecule in mixtures with helium. Many of the values, especially for the overtone transition, are novel. The uncertainties for the isotope-averaged broadening coefficients amount to 2% on average for the fundamental and 1.5% for the overtone bands. Shifts have a typical uncertainty of 3%. GRAPHICAL ABSTRACT

Infrared spectra of thin films of α-crystalline hexafluoroethane: a manifestation of resonant dipole–dipole interaction in the range of fundamental vibrational modes ν5 and ν10

Infrared reflection-absorption spectra of thin films of α-crystalline hexafluoroethane deposited on a gold-plated copper mirror are measured at temperatures of 70 and 80 K. The bands corresponding to strong in the dipole absorption vibrations ν5 and ν10 have complex contours, the shape of which is explained in terms of the resonant dipole–dipole interaction between identical spectrally active molecules of the crystal. Splittings of the complex ν5 and ν10 bands are explained taking into account two effects: the Davydov splitting and the LO–TO splitting of the strong modes. Bands of the asymmetric 13С12СF6 isotopologue in the absorption spectrum of the crystal exhibit an anomalously large isotope shift as compared with the shift in the spectrum of free molecules. This anomaly is explained by intermolecular resonant dipole–dipole interaction of asymmetric 13С12СF6 isotopologue with molecules of the environment, consisting of the most abundant 12C2F6 isotopologue. The correctness of the given interpretation is confirmed calculating these three effects in the model of resonant dipole–dipole interaction.