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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.

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.

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.

Quantum chemical calculations for possible conformers of the melatonin molecule (N-acetyl–5-methoxytryptamine) and its two catabolites, (N-γ-acetyl-N-formyl-5-methoxykynuramine (AFMK) and N-γ-acetyl-5-methoxykynuramine (AMK)), are performed at different theoretical levels with inclusion of the macrohydration effects within the conductor-like polarizable continuum model (CPCM). The influence of the used in biochemical studies CD3-labels on the vibrational spectra of molecules is considered. It is demonstrated that the theoretical (B3LYP/6-31+G**) vibrational spectra and geometric parameters of the most stable melatonin conformers are in good agreement with the experimental data. On a base of analysis of the theoretical frequency shifts in the theoretical B3LYP/6-31+G** vibrational spectra of different conformations of melatonin catabolites and of the influence of the aqueous surrounding and isotopic substitution, the conclusion is made that the region of nitrogen–hydrogen stretching can be proposed for identification of considered compounds.

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.

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.

IR absorption and Raman spectra of N-methylacetamide and (1S,5S,6R)-6-acetylamino-(5′-methoxyindolo[2,3-b])bicyclo[3.2.1]oct-2-ene are investigated. Optimized structures and harmonic force fields of stable conformers of both compounds are obtained by means of MP2 and DFT (B3LYP) methods using the 6-31+G** basis set. Based on quantum mechanical calculations, a detailed interpretation of spectra is proposed and vibrational frequencies of the most stable conformations are assigned. Correlations between structures and the spectra of N-methylacetamide and (1S,5S,6R)-6-acetylamino-(5′-methoxyindolo[2,3-b])bicyclo[3.2.1]oct-2-ene were considered and analytical spectral regions were proposed.

Quantum-chemical calculations of the optimized structures, harmonic force fields, and frequencies of 1 : 1 and 1 : 2 complexes of 2-(2′-pyridyl)-benzimidazole and 1-methyl-2-pyridine-2-yl-1H-benzimidazole are performed by means of DFT (B3LYP/6-31+G**). The shifts in the frequencies of the vibrational spectra of the investigated complexes are considered with allowance for the conformational structure and effect of the medium. Analytical bands (spectral marks) are proposed that can be used to identify complexes of 2-(2′-pyridyl)-benzimidazole and 1-methyl-2-pyridine-2-yl-1H-benzimidazole with water. It is concluded that considering the environment within a model of a polarized continuum allows the forecasting of possible shifts in the frequencies in the vibrational spectra of the studied compounds in aqueous media and DMF.

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 (S 0) 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 18 1 1 .

The adsorption of silver clusters Ag n (n = 1–7) on different sites of an α-SiO2 (0001) surface is studied using density functional theory calculations in the general gradient approximation. The most stable configurations of Ag n (n = 1–7) adsorbed on the α-SiO2 surface are determined, and the correlations between cluster size and adsorption energy are found. It is established that the optimized geometry parameters of Ag n (n = 1–7) and the values of their adsorption energy are in good agreement with the results from earlier investigations and confirm the validity of the chosen theoretical model.

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 (S 1) 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 (S 1) 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 (S 1) electronic state.

Detailed studies of the molecular and electronic structures, vibrational frequencies, and infrared intensities of [M−] and [M-H−] anions of aniline and its derivatives (2-, 3-, 4-fluoroanilines, N-[(2E)-1-methylbut-2-en-1-yl]aniline, (2-cyclopent-2-en-1-ylphenyl)amine, N-[(2E)-1-methylbut-2-en-1-yl]aniline, and N-cyclopent-2-en-1-ylaniline) have been carried out using the density functional method with UB3LYP functional and 6-31G** basis set augmented with sp diffuse functions on nitrogen, fluorine, and three carbon atoms of benzene ring (in 2, 4, and 6 positions). For comparison, similar calculations were carried out for the closed-shell neutral molecules ([M]). The studies have provided detailed insight into the structure changes that take place in negative ions of aniline and its derivatives.

Quantum-mechanical calculations of optimized structures, harmonic force fields, and vibrational spectra were performed for 10 L-glutamic acid conformers. The vibrational spectra were interpreted using B3LYP/6-31+G** calculations for the stablest conformer. Satisfactory agreement between the experimental and theoretical data was obtained. Vibrational frequency shifts caused by isotopic substitution of various types in the L-glutamic acid molecule were analyzed taking into account the conformational structure and the influence of water medium and molecule ionization. Isotopic tags are suggested that can be used in biochemical studies taking into account their special characteristics.

The vibrational structure of the UV absorption spectrum of acryloyl chloride vapor was analyzed to obtain detailed information about the torsional vibration levels of the trans and cis isomers in the ground (S0) and excited (S1) electronic states. The spectrum contained 114 absorption bands of which ∼90% were assigned. The 0-0 transition frequencies of the trans and cis acryloyl chloride isomers were determined. Several Deslandres tables for torsional vibrations from the 0–0 transition frequencies and local origins corresponding to the fundamental frequencies of two isomeric molecule forms in both electronic states were constructed. The corresponding systems of torsional vibration levels were determined, and the harmonic frequencies θe and anharmonicity coefficients x11 of the trans and cis isomers were calculated. The torsional vibration levels in the ground electronic state obtained from the vibrational structure of the UV spectrum are compared with those determined using the Fourier spectrum. The 0–3 torsional transition of the trans isomer was found to be displaced because of Fermi resonance with a fundamental frequency.

The systems of torsional vibration levels of the trans and cis methacryloyl chloride isomers in the ground (S 0) and excited (S 1) electronic states obtained by analyzing the vibrational structure of the gas-phase UV spectrum were used to reproduce the internal rotation potential functions of the molecule in both electronic states. The kinematic F factor in the S 0 and S 1 electronic states was calculated taking into account the relaxation of geometric parameters depending on the internal rotation angle. The internal rotation potential function parameters in the S 0 state are substantially different from the parameters obtained using the torsional levels of the IR Fourier transform spectrum; at the same time, they are substantiated by quantum-mechanical calculations.

Quantum-mechanical calculations of the optimized structures, barriers to internal rotation about the Si-C bond, harmonic force fields, and vibrational frequencies of CCH3SiF3, CH2ClSiF3, CHCl2SiF3, and CCl3SiF3 were performed using the Hartree-Fock approximation and density functional theory at the MP2/6-31G*, B3LYP/6-31G*, B3LYP/6-311++G**, B3LYP/aug-cc-pVDZ, and B3LYP/aug-cc-pVTZ levels. A new interpretation of the infrared absorption and Raman spectra of the compounds was suggested on the basis of the theoretical results

The internal rotation potential function of the acryloyl chloride molecule in the S 0 and S 1 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 S 0 ground state was calculated including geometric parameter relaxation as a function of internal rotation angle. The torsional potential parameters in the S 0 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.

The laser-excited Raman spectra of liquid CH3SiClnBr3−n (n = 0, 1, 2) were studied. Quantumchemical calculations of these substances with geometry optimization were performed to determine their harmonic force fields and vibrational frequencies. The calculations were made using the HF/6-31G* and HF/6-311++G** approximations and density functional theory at the B3LYP/6-31G* and B3LYP/6-311++G** levels. An interpretation of the spectra was suggested and the calculated force fields were discussed in comparison with the data on related compounds.

The infrared spectra (4000–400 cm− 1) of solid and the Raman spectra (3500–30 cm− 1) of liquid and solid 1-nitropropane, CH3CH2CH2NO2, have been registered. Both the trans and gauche conformers have been identified in the fluid phase, while the trans form remains in the stable solid. Temperature dependence (190–230K) of the liquid 1-nitropropane Raman spectra has been carried out. From these data, the enthalpy difference was determined to be 870 ± 105 J-mol−1, with the gauche conformer being the more stable rotamer. Ab initio and DFT calculations at different levels of approximation (HF, MP2, B3LYP, B3PW91) gave optimized geometries, harmonic force fields, and vibrational frequencies for the trans and gauche conformers. All the calculations (except the B3PW91/6-31G* level) predicted gauche as the low-energy conformer. Theoretical force constants are analyzed for formulating constraints in the molecular force field model of 1-nitropropane.

Infrared and Raman spectra of 1,2-difluoro-1,1,2-trichloroethane (DFTCE) were measured in the gaseous, liquid and glassy states within a wide temperature interval. The complete assignment of the spectra was made on the basis of experimental information and theoretical (ab initio and DFT) force field calculations. It was found that in all aggregate states the substance existed as a mixture of three conformers, the most stable having trans-position of C–Cl bonds. Enthalpy differences between conformers in the gaseous phase were determined to be 1.93±0.25 (t−g + ), 0.75±0.20 (t−g − ) and 1.09±0.20 (g − −g + ) kJ mol −1 . The potential function of internal rotation (PFIR) was estimated from the torsion fundamentals and calculated at the HF/6-31G∗ and B3LYP/6-31G∗ levels of theory.

Ab initio and DFT results on harmonic force constants for trans - and gauche -conformers of CH 3 CH 2 CH 2 Cl, CF 3 CH 2 CH 2 Cl and CCl 3 CH 2 CH 2 Cl are used for formulating constraints in molecular force field models described compounds with hindered internal rotation around the C–C bond.

The fully optimized geometries and vibrational frequencies of trans - and gauche -conformers of CF 3 CH 2 CH 2 Cl and CCl 3 CH 2 CH 2 Cl were obtained at the B3LYP and BLYP levels of hybrid functional theory DFT with the different basis sets. Corresponding ab initio calculations were also performed at the HF and MP2 levels of theory. DFT calculations using Becke's exchange and Lee–Yang–Parr correlation functional give a correct picture of the relative stability of different conformers and present rather good agreement of calculated and experimental frequencies. On this basis, the regularized quantum mechanical force field (RQMFF) for both trans - and gauche -conformers of CF 3 CH 2 CH 2 Cl and CCl 3 CH 2 CH 2 Cl were obtained.

We present a systematic application of Tikhonov’s regularization method to joint treatment of ab initio and experimental vibrational data for a series of mono-, di-, and tri-substituted haloethanes, based on uniform MP2/6-31G* level of theory. This leads to MP2/6-31G*-“regularized” force field parameters that exactly reproduce experimental frequencies and isotopomer shifts (within prescribed error levels) and are “closest” (in Euclidean norm) to the ab initio force field. We correct a number of previous experimental spectral assignments and investigate the limits of transferability (e.g., of methyl-group force field parameters from one species to another) and other common simplifying approximations (e.g., MVFF modified valence force field treatment). Our results demonstrate how one can systematically combine experimental and ab initio information to create a data base of freon-type force field parameters having greater accuracy and reliability than could be obtained from theory or experiment alone.

The direct and inverse vibrational problems are solved for the rotational isomers of the glyoxal and oxalyl halide molecules in the ground and first excited singlet states.

The IR and Raman spectra of bis(N-2-chloroethyl)nitramine (BCENA) in the liquid and crystalline states and in CCl4 and CH3CN solutions are studied. The spectra are compared, and it is concluded that BCENA exists as a mixture of conformers of different polarities in the liquid state and as one less polar conformer in the crystalline state. To determine the conformations corresponding to the total electron energy minima and interpret the vibrational spectrum of BCENA, we performed an ab initio quantum chemical calculation of the BCENA molecule in the Hartree-Fock approximation using the 3–21G* and 6–31G* basis sets. Out of twelve possible conformations five are stable; the most stable conformer is C2(GG). The frequencies and forms of normal vibrations of stable conformers are calculated using scaled quantum chemical force fields. The calculated and experimental frequencies are compared, and the relations between the frequencies of skeletal stretching and bending vibrations are analyzed. It is concluded that the BCENA crystal is formed by the C2 (GG) conformer. The vibrational spectrum is interpreted, and the frequencies are assigned to vibrations of conformers differing in form.

A new approach to the analysis of the force fields of polyatomic molecules is discussed. The results of quantum chemical calculations in combination with experimental data are used in a regularizing procedure, where the nonempirical matrix of the force constants determines the stabilizer of Tikhonov's functional. The use of stable numerical methods allows the specific modeling of the force fields of polyatomic molecules with due account of rotational isomerism.

We describe a novel method for employing calculated ab initio potential data together with Tikhonov’s variational procedure to extract fundamental molecular force field parameters from experimental spectral data, the formal ‘‘inverse problem’’ of vibrational spectroscopy. In this approach, the ab initio quantities serve to ‘‘regularize’’ the initially ill‐posed problem (in the sense of Tikhonov), leading to variationally stable and unique force field parameters that optimally mimic overall patterns of the (approximate) ab initio quantities, but exactly reproduce the available experimental data within specified experimental precision. In this manner, ab initio and experimental data can be jointly combined to produce more stable and reliable force fields (improvable to any degree through higher level ab initio treatment, additional experimental data, etc.) than could be attained by theoretical or experimental methods alone. The proposed procedure allows use of any system of generalized coordinates, including redundant systems of internal or symmetry coordinates, simplifying the transfer and comparison of force constants in series of related molecules. The procedure is illustrated with numerical application to CHF2Cl and its isotopomers at MP2/3‐21G*, MP2/6‐31G* levels of theory, demonstrating the stability and consistency of force fields obtained from different levels of theoretical input.

Stable numerical methods for constructing molecular force fields on the basis of experimental data using Tikhonov's regularization method of ill-posed problems are proposed.

Infrared and Raman spectra of t , T , t -2,3,4,5-tetrachlorohexa-1,3,5-triene were measured in liquid and crystalline phases. It is suggested that the non-planar structure of this compound may be due to the 1–3 effect. In the liquid state a mixture of rotational isomers, of C 2 and C i symmetry, was confirmed by the freezing-out of some characteristic bands in the 1600 cm −1 region in the IR and Raman spectra of the t , T , t -compound. Normal coordinate analysis was carried out using force constant values from the force field previously determined for chloroderivatives of buta-1,3-diene. A complete assignment of observed frequencies is proposed.

The Raman (50–3200 cm−1) and infrared (50–3200 cm−1) spectra of bis(N-ethyl)nitramine, (CH3CH2)2NNO2, in the liquid and crystal states have been recorded. Optimized geometries and conformational stabilities have been obtained from ab initio calculations utilizing the RHF/6-31G∗∗ level. This compound was shown to have two stable conformations with a planar nitramine fragment and the CH3 groups orthogonal to it and located either on the same or on the different sides of it. The computed energy difference between two conformers is 0.57 kcal/mol. (CH3CH2)2NNO2 exists as a mixture of the two conformations in the liquid state, while only the most stable one, with the CH3 groups located on the different sides of the nitramine fragment, remains in crystal state. The vibrational frequencies have been calculated using ab initio scaled force fields, and the vibrational spectra have been interpreted in detail.

A complete optimization of the nitromethane geometry at the HF/6-31G and HF/ 6-31G* (5D) levels for staggered (one CH bond situated in a plane perpendicular to the plane of the heavy atoms) and eclipsed conformations is reported. The geometrical parameters obtained for the staggered conformation are in quite good agreement with the microwave structure (ref. 1). The effect of electron correlation on the energy difference between the two conformers is estimated using single point MP4SDQ/6-31G* calculations at the 6-31G geometry. The harmonic force field for both conformers are calculated at the HF/6-31G//HF/6-31G level. Taking into account the known overestimation of the vibrational frequencies by ∼20% in ab initio calculations, the experimental frequency assignment is confirmed. The six scale factors for the force field were evaluated using the experimental frequencies of nitromethane and nitromethane-d 3 (ref. 2). The vibrational frequencies for the five isotopomers of staggered nitromethane are determined with the scaled quantum mechanical force field (SQMFF). A detailed interpretation of conformational effects in the IR spectrum of crystalline CHD 2 NO 2 is proposed.

Force fields and mean amplitudes of vibration of chromium, molybdenum and tungsten hexafluorides and dioxodifluorides are calculated using Tikchonov's regularization method and are compared with those for oxotetrafluorides.

Force fields and mean amplitudes of vibration of CH2ClSiH3, CHCl2SiH3, CCl3, SiCl3 and CCl3SiF3 are calculated using Tikhonov's regularization method. The transferability of calculated force constants is examined by normal coordinate calculations for CH2ClSiF3, CH2ClSiCl3, CHCl2SiF3, CHCl2SiCl3 and CCl3SiH3.

1-(2-Furyl)-3-amino-4,4-dimethylpentane was used to obtain 3-tert-butyl-1,2-dihydropyrrolizine, the catalytic hydrogenation of which over Rh/Al2O3 at room temperature gives a mixture of cis- and trans-3,8-H-3-ter-butylpyrrolizidines with predominance of the cis isomer, whereas hydrogenation at 90–100 °C gives a mixture containing the trans isomer as the principal component. The three-dimensional structures of the isomers follow from data on the catalytic hydrogenation and isomerization and the IR, Raman, and PME spectra. A considerable percentage of the trans-fused form is characteristic for cis-3,8-H-3-tert-butylpyrrolizidine.

A complete interpretation of the vibrational spectra of chloroprene, 2,3-dichlorobuta-1,3-diene, 1,1,2,3-tetrachlorobuta-1,3-diene, 1,1,2,3,4-pentachlorobuta-1,3-diene and hexachlorobuta-1,3-diene has been carried out and a normal coordinate analysis of these molecules has been performed. The conclusion about the non-planar conformation of the last three molecules was drawn from results of the CNDO/2 conformational calculations. The applicability of the CNDO/2 method to the molecules with the conjugated double bonds is discussed.

8. J. A. Barltrop and J. D. Coyle, Excited States in Organic Chemistry [Russian transla- tion], Moscow (1978), pp. 67"70. 9. I. S. Ioffe and V. F. Otten, Zh. Organ. Khim., 32, No. 4, 1196-1201 (1962). i0. I. S. Ioffe and V. F Otten, Zh. Organ. Khim., i, No. 2, 343-346 (1965). ii. Yu. Yu. Lur'e, Handbook on Analytical Chemistry [in Russian], Moscow (1979), p. 322. 12. B. Stevens, N. Conneily, and P. Suppan, Spectrochim. Acta, 2-2, No. 12, 2121-2122 (1966). 13. Sharma Ashutash and M. K. Machwe, Curr. Sci. (India), 5_~i, No. 13, 657-659 (1982). 14. M. D. Galanin, A. A. Kut'enkov, V. N. Smorchkov, et al., Opt. Spektrosk., 53, No. 4, 683-689 (1982). 15. V. Ya. Artyukhov, R. T. Kuznetsova, and R. M. Fofonova, Zh. Prikl. Spektrosk., 37, No. 4, 576-580 (1982). 16. F. V. Schaefer (ed.), Dye Lasers, Springer, New York (1977). VIBRATIONAL SPECTRA AND CONFORMATIONAL C~9OSITION OF ETHYLENE GLYCOL DINITRATE IN SOLID PHASES G. A. Beresneva, L. V. Khristenko, UDC 539.194.01 S. V. Krasnoshchekov, and Yu. A. Pentin The authors of [i] studied the vibrational spectra of ethylene glycol dinitrate (EGDN) and showed that in the liquid state this compound consists of a mixture of conformers, while in the crystalline state it exists in the form of two modifications: a metastable one (crystal II), obtained by intense supercooling the liquid, and a stable modification (crystal I) obtained by either slowly cooling the liquid, or by heating the metastable modification to a temperature of -50~ If we assume that in a restrained internal rotation around the C--C and C--O bonds, the "staggered" conformations will be stable, while the --C-~NO= groups are planar, then EGDN can exist in the form of ten different nuclear equilibrium configurations. Figure i shows these possible conformations of EGDN. The authors of [i] suggested that each of the solid modifications is formed by only one of the ten possible conformers, which were identified from the data of rotation isomerism of ethyl nitrate [2] and the results of vibrational calculation carried out in [3], using force constants obtained by the MINDO/2 method. In this present work, the IR spectra of crystals I and II were recorded on a Bruker Fourier-type spectrometer with a higher,resolution than that obtained in [i], including the region below 400 cm -I, in which the IR spectra of crystals have not yet been studied. Figure 2 shows the IR spectra of a vitreous EGDN and two of its crystalline modifications (I and II). In the spectrum of crystal II in the 100-900 cm -I region, a region of skeletal stretch- ing and deformational vibrations, which are most sensitive to rotation isomerism, the number of bands exceeds that required for one nuclear configuration at equilibrium. On crystal II § crystal I transition, the bands at 213, 390, 588, 662, 715, 862, 928, i036,'1237, 1392, 1431, 1460, and 1646 cm -i disappear. Bands at 364, 405, 581, 656, 680, 937, 1044, 1232, 1309, 1396, 1422, 1449, and 1666 cm -~, with a low intensity in the spectrum of crystal II, become markedly more intense, and the number of bands in the spectrum of crystal I in the 100-900 cm -i region corresponds to the number of bands for one Conformer. These facts indicate that crystal II is formed by at least two conformers, and crystal I by one conformer, and the conformer forming crystal I is also included in the composition of crystal II. For a more reliable identification of the conformers forming crystals I and II, we calculated the frequencies and forms of normal vibrations of all the ten possible conformers of EGDN. The calculations were carried out in an independent system of local symmetry co- ordinates, by a standard method [4]. The natural coordinates introduced, which are repre- Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 48, No. 6, pp. 946-952, June, 1988. Original article submitted April 8, 1987. 614 0021-9037/88/4806-0614512.50 9 1988 Plenum Publishing Corporation

The problem of constructing a stable algorithm for the solution of the inverse vibrational problem in the case of polyatomic molecules (with the use of data on Isotopically substituted compounds) in a complete system of dependent natural coordinates was presented to us. Our formulation of the problem has been presented in [2]. Let Z be the linear space of real symmetric matrices of dimensionality n x n, in which the closeness of the matrices is characterized by the Euclidean norm for vectors of dimensionality n(n + 1)/2 which are composed of the elements lying on or above the principal diagonals of the matrices. Let T-I~Z be the prescribed positive definite symmetric matrix of the kinematic coefficients and let A be an operator which correlates to each matrix U~Z, an ordered (in order of increasing size, for example) set (a vector from the Euclidean space R n) of eigenvalues of the matrix T-*U, i.e., the vector of the squares of the frequencies of the normal vibrations A~R =. The operator A is defined and continuous everywhere on Z. The problem of determin

The 3,3-dimethyl-3-silathietane molecule has been investigated by gas-phase electron diffraction analysis with consideration of the vibrational effects. The following geometric parameters were obtained (the distances ra, the angles L~, the errors in the form of 3o in parentheses, for ~ 50): S-C 1.853(4), Si-C m 1.870(5) (m stands for methyl), Si-C r 1.916(3) (r stands for ring), C-H 1.086(3) ~, L(C-Si-C) m = 106.9(7), L(C-Si-C) r = 86.1(3), LSi-C-S = 90.5(5), and LC-S-C = 89.5(4) ~ The fourmembered ring is nonplanar; the angle 9 between the CSiC and CSC planes equals 2 0 . 3 ( 2 0 ) ~

The vibrational spectra of CF 3 CH 2 CH 2 Cl in different states of aggregation is investigated and the normal coordinate analysis of trans - and gauche -conformers is carried out. The assignments in vibrational spectra for both the conformers of CF 3 CH 2 CH 2 Cl are given. It is shown that the stable crystalline modification, crystal II, is formed by the trans -conformer of the molecule.