L. A. Koroleva

An analysis of the vibrational structure of the UV absorption spectrum of methacryloyl chloride vapor

An analysis of the vibrational structure of the UV spectrum of methacryloyl chloride vapor was performed. The spectrum contained unique information about the torsional vibration levels of the trans and cis isomers in the ground (S0) and excited (S1) electronic states. 136 absorption bands were revealed, and ∼85% of them were assigned. The 0-0 transition frequencies of the trans and cis isomers were found. Several Deslandres tables were constructed for torsional vibrations from 0-0 transition frequencies and “local origins” corresponding to fundamental and combined frequencies of both isomers. Systems of torsional levels up to high quantum number values (v ≈ 6–8) were determined, and the ωe harmonic frequencies and χ11 anharmonicity coefficients were calculated for both isometric forms in the ground (S0) and excited (S1) states. The results were substantially different from those obtained in an analysis of Fourier-transform IR spectra.

An analysis of the vibrational structure of high-resolution UV spectra and long-wave IR Fourier transform spectra in studies of internal rotation in molecules

The methods for analyzing the vibrational structure of high-resolution UV spectra and long-wave IR Fourier transform spectra in studies of internal rotation in α,β-unsaturated carbonyl compounds R4R3C=CR2-COR1 (R1 = F, Cl; R2 = R3 = R4 = H, CH3) are compared. These methods were found to give different experimental values for systems of torsional vibration energy levels up to high quantum numbers, torsional frequencies (0–1 transitions), and anharmonicity coefficients x11 for trans and cis isomers of the same molecules in the ground electronic state (S0). It was shown that the experimental technique for analyzing the vibrational structure of UV spectra excludes the hydrolysis of compounds under study. Taking into account Fermi resonance and numerous Deslandres tables constructed for trans and cis isomers provides reliable determination of values necessary for the construction of internal rotation potential functions, because they are multiply repeated in various Deslandres tables. An analysis of the vibrational structure of UV spectra gives more reliable Vn internal rotation potential function parameters. The Vn parameter values were substantiated by quantum-mechanical calculations performed by other authors.

Analysis of the vibrational structure of the n-π* transition in the high-resolution UV absorption spectrum of methacrolein vapor

The bands of the vibrational structure of the n-π* transition in the high-resolution UV absorption spectrum of methacrolein vapor were assigned. The 0–0 transitions of the s-trans- and s-cis-isomers were evaluated: ν00trans = 26484.3 cm−1, ν00cis = 25288.8 cm−1. The fundamental vibration frequencies of both isomers were found not only for the ground state, but also for the excited one. The harmonic frequencies ωe and anharmonicity coefficients x11, as well as the frequencies of the 0-υ transitions of the torsional vibrations in both electronic states up to high values of the vibrational quantum number υ, were determined from the Deslandres tables constructed for the s-trans-isomer.

Comparative analysis of the vibrational structure of the absorption spectra of acrolein in the excited (S 1) electronic state

The assignments of absorption bands of the vibrational structure of the UV spectrum are compared with the assignments of bands obtained by the CRDS method in a supersonic jet from the time of laser radiation damping for the trans isomer of acrolein in the excited (S1) electronic state. The ν00trans = 25861 cm−1 values and fundamental frequencies, including torsional vibration frequency, obtained by the two methods were found to coincide in the excited electronic state (S1) for this isomer. The assignments of several absorption bands of the vibrational structure of the spectrum obtained by the CRDS method were changed. Changes in the assignment of (0-v′) transition bands of the torsional vibration of the trans isomer in the Deslandres table from the ν00trans trans origin allowed the table to be extended to high quantum numbers v′. The torsional vibration frequencies up to v′ = 5 were found to be close to the frequencies found by analyzing the vibrational structure of the UV spectrum and calculated quantum-mechanically. The coincidence of the barrier to internal rotation (the cis-trans transition) in the one-dimensional model with that calculated quantum-mechanically using the two-dimensional model corresponds to a planar structure of the acrolein molecule in the excited (S1) electronic state.

Internal rotation potential functions of the acryloyl chloride molecule in the ground (S 0) and excited (S 1) electronic states

The internal rotation potential function of the acryloyl chloride molecule in the S0 and S1 electronic states was reproduced using systems of torsional vibration levels obtained for its trans and cis isomers by analyzing the vibrational structure of the UV spectrum of the molecule. The kinematic factor F in the S0 ground state was calculated including geometric parameter relaxation as a function of internal rotation angle. The torsional potential parameters in the S0 state obtained in this work were substantially different from those determined from the infrared Fourier-transform spectrum ignoring the resonance perturbation of the level with v = 3. The form of the internal rotation potential function and the higher stability of the trans isomer (the main isomer) were substantiated by high-level quantum-mechanical calculations.

Internal rotation potential functions of an acryloyl fluoride molecule in the ground ( S 0 ) and excited ( S 1 ) electronic states

Structural parameters of trans- and cis-isomers of an acryloyl fluoride molecule in the ground (S0) and excited (S1) electronic states are determined. The F(φ) function is expanded into the Fourier series. The internal rotation potential functions (IRPFs) of acryloyl fluoride in both electronic states are derived. To this end, torsional vibrational transition frequencies of both isomers of this molecule were used, which were obtained from the analysis of the vibrational structure Щf a high resolution UV spectrum of acryloyl fluoride vapor with regard to the geometry and energy difference (ΔH) of the isomers. The IRPF parameters Vn of this molecule in the (S0) state, which were derived based on the transition frequencies of torsional vibrations from the vibrational structure of the high resolution UV spectrum and the IR Fourier spectrum coincided.

Analysis of the Vibrational Structure of the n–π* Transition in the High-Resolution UV Absorption Spectrum of Methacryloyl Fluoride in the Gas Phase

The UV absorption spectrum of methacryloyl fluoride molecule in the gas phase is obtained in the wavenumber range of 32300–35900 cm−1. The resolved vibrational structure of this spectrum consists of 153 absorption bands. The assignment of all bands has been made for the first time. Values ν00trans = 35670.0 сm−1 and ν00cis = 35371.1 cm−1 are determined. The fundamental frequencies for isomers in the S0 and S1 states are found. Several Deslandres Tables (DTs) are constructed for the torsional vibration of the s-trans- and s-cis-isomers of the investigated molecule using the NONIUS program. The origins in these DTs correspond to bands attributed to ν00, and to the fundamental frequencies of each isomer in states S0 and S1. These DTs are used to determine harmonic frequencies ωe, anharmonicity coefficients х11, and the frequencies of torsional vibration 0–v transitions up to high values of vibrational quantum number v for s-trans- and s-cis-isomers in both electronic states. The frequencies of torsional vibrations for the s-trans-isomer and the s-cis-isomer in the S0 state are ν″1 = 80.9 сm−1 and ν″1 = 59.8 сm−1, respectively. The frequencies for the s-trans- isomer and the s-cis-isomer in the S1 state are ν′1 = 134.1 сm−1 and ν′1 = 103.6 cm−1, respectively.

Changes in the IR Spectra of Aqueous Solutions of Alkali Metal Chlorides during Crystallization

The IR spectra of aqueous solutions of sodium chloride and rubidium chloride with the same concentration of 0.1 M upon freezing are studied in the middle IR region. The changes that occur in the absorption bands of the bending ν2, compound ν2 + νL, and stretching (ν1, 2ν2, and ν3) vibrations of water molecules with gradual crystallization of the solutions are studied. The obtained spectra of crystallized solutions are compared to the IR spectrum of ice Ih. Analysis allows conclusions about the structure of the investigated frozen crystallized solutions.

Potential function of the internal rotation of a methacrolein molecule in the ground (S 0) electronic state

The structural parameters of s-trans- and s-cis-isomers of a methacrolein molecule in the ground (S0) electronic state are determined by means of MP2 method with the cc-pVTZ basis set. Kinematic factor F(φ) is expanded in a Fourier series. The potential function of internal rotation (PFIR) of methacrolein in this state is built using experimental frequencies of transitions of the torsional vibration of both isomers, obtained from an analysis of the vibrational structure of the high-resolution UV spectrum with allowance for the geometry and difference between the energy (ΔH) of the isomers. It is shown that the Vn parameters of the potential function of internal rotation of the molecule, built using the frequencies of the transition of the torsional vibrations of s-trans- and s-cis-isomers of the methacrolein molecule, determined from vibrational structure of the high-resolution UV spectrum and the FTIR spectrum, are close.

Analysis of methods for calculating the transition frequencies of the torsional vibration of acrolein isomers in the ground (S 0) electronic state

B3LYP, MP2, CCSD(T), and MP4/MP2 in the 6-311G(d, p), 6-311++G(d, p), cc-pVTZ, aug-cc-pVTZ bases used to calculate the transition frequencies of torsional vibration of trans- and cis-isomers of acrolein in the ground electronic state (S0) are analyzed. It is found that for trans-isomers, all methods of calculation except for B3LYP in the cc-pVTZ basis yield good agreement between the calculated and experimental values. It is noted that for the cis-isomer of acrolein, no method of calculation confirms the experimental value of the frequency of torsional vibration (138 cm−1). It is shown that the calculated and experimental values for obertones at 273.0 cm−1 and other transitions of torsional vibration are different for this isomer in particular. However, it is established that in some calculation methods (B3LYP, MP2), the frequency of the torsional vibration of the cis-isomer coincides with another experimental value of this frequency (166.5 cm−1). It is concluded that in analyzing the vibrational structure of the UV spectrum, the calculated and experimental values of its obertone (331.3 cm−1) coincide, along with its frequency. It is also noted that the frequency of torsional vibration for the cis-isomer (166.5 cm−1) can also be found in other experimental works if we change the allocation of torsional transition 1811.