Isotopic effect in anharmonic vibrational spectra of molecules

V. I. Vernadskii Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences. Translated fromZhurmal Strukturnoi Khirnii, Vol. 36, No. 6, pp. 1144–1146, November–December, 1995.     

Prediction of the vibrational spectra of interacting water molecules

A system of computer programs has been developed to predict and interpret the infrared spectra of molecules, ions, radicals and of chemically interacting species. The frequency parameters (or force constants) and the intensity parameters (or atomic polar tensors (APTs)) are calculated using the Gaussian-76 program for $\text{ab}$$\text{initio}$ quantum mechanical calculations with a 4–31G basis set. The resultant wavenumbers and intensities have been used to predict the fundamental infrared spectra of water molecules interacting with different molecular species. The corresponding wavenumber shifts and intensity changes from the spectrum of the non-interacting water molecule are dependent upon both the geometrical orientation and the electron-donating properties of the interacting species. The intensity parameters can be further analyzed by using the charge-charge flux-overlap (CCFO) interpretation of the APTs. This interpretation is helpful in pinpointing the exact source of the perturbation that produces the intensity change. The significance is discussed of each of these CCFO terms in predicting the infrared intensities of molecules undergoing intermolecular interaction.     

Band shape in vibrational spectra and interactions of polar molecules in liquids

The structure and shape of bands in the Raman vibrational spectra of polar molecules in liquids are analyzed. The possibility of using these data to examine interactions of molecules as well as their vibrational and orientational dynamics is shown. Translated from Zhumal Struktumoi Khimii, Vol. 38, No. 2, pp. 270–281, March–April, 1997.     

Density functional theory study of vibrational spectra of acridine and phenazine

Density functional theory (DFT) calculations using Becke's exchange in conjunction with Lee-Yang-Parr's correlation functionals (BLYP), Becke's three-parameter hybrid DFT/HF method using Lee-Yang-Parr's correlation functionals (B3LYP) and ab initio Hartree-Fock (HF) method have been carried out to investigate the structure and vibrational spectra of acridine and phenazine. Structural parameters obtained by B3LYP/6-31G* geometry optimization are in good agreement with available experimental data. The raw BLYP non-CH stretching frequencies approximate the experimental results much better than the HF results with the mean absolute deviation about 16 cm(-1). The scaled B3LYP frequencies are more reliable than that of the BLYP and HF methods with the mean absolute deviation about 17 cm(-1). On the basis of the comparison between calculated and experimental results, assignments of fundamental vibrational modes are examined. Also the structure and vibrational frequencies are compared with those of anthracene, pyridine and benzene to study the similarities and differences.     

Theoretical calculation of the vibrational spectra of some XHn type molecules

The potential function of some molecules of type XH_n has been obtained by a priori calculations of the total energy, within the Born Oppenheimer approximation, for several geometrical configurations. These functions have been used to calculate the simply excited vibrational levels. The calculated values of the electric dipole moment for the different geometrical configurations has enabled the computation of its derivative with respect to the nuclear coordinates. The results reported are critically discussed and some explanations are presented to justify the discrepancies found with the experimental data.

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Zusammenfassung Mittels einer apriorischen Berechnung der Gesamtenergie nach der Born-Oppenheimer-Methode ist die Potentialfunktion für einige Moleküle der Art XH_n in verschiedenen Konfigurationen erhalten worden. Diese Funktionen sind für die Berechnung der monoerregten SchwingungszustÄnde gebraucht worden. Die berechneten Werte des elektrischen Dipolmoments für verschiedene Geometrien haben die Berechnung der Ableitungen des Dipolmoments nach den Kernkoordinaten erlaubt. Die erhaltenen Resultate werden diskutiert und einige ErklÄrungen vorgeführt, um die gefundenen Unterschiede von den experimentellen Ergebnissen zu klÄren.

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Résumé La fonction potentiel de quelques molécules XH_n a été obtenue par le calcul a priori de l'énergie moléculaire, dans l'approximation de Born et Oppenheimer, pour plusieures configurations géométriques. Ces fonctions ont été utilisées pour calculer les vibrations monoexcitées. Les valeurs calculées du moment de dipole électrique pour différentes configurations donnent la possibilité de calculer ses dérivées par rapport aux coordonées nucléaires. On donne des justifications a l'accord peu satisfaisant entre les résultats et l'expérience.

     

儿茶素结构和振动光谱的密度泛函理论研究

本文利用密度泛函理论方法B3LYP在6-311 G(d,p)水平上研究了儿茶素及其异构体表儿茶素分子的几何构型,计算结果与实验所得结构参数一致.计算了儿茶素分子平衡构型下的力常数,使用Wilson的GF矩阵方法计算了振动基频以及相应的势能分布,据此结合理论计算的光谱强度,对儿茶素分子的振动基频进行了完善合理的理论归属.     

Hypervirial SCF treatment for vibrational energy levels of triatomic molecules

The SCF method for the calculation of energy levels of triatomic molecules is applied using the hypervirial perturbative procedure for solving the coupled equations. This treatment allows to obtain in a recursive way the energy corrections and the expectation values required in the SCF treatment, avoiding the explicit calculation of the wave functions. A numerical application is made to the SO₂ and O₃ molecules, comparing our results with those obtained by other methods.     

Density functional theory calculations and vibrational spectra of 6-methyl 1,2,3,4-tetrahyroquinoline

The solid phase FTIR and Raman spectra of 6-methyl 1,2,3,4-tetrahydroquinoline (MTHQ) have been recorded in the regions 4000-100 and 3500-100 cm(-1), respectively. The spectra were interpreted with the aid of normal coordinate analysis following a full structure optimization and force field calculations based on the density functional theory (DFT) using the standard B3LYP/6-311+G(**) basis set combination. A close agreement was achieved between the observed and calculated frequencies by refinement of the scale factors.     

Microwave spectra ofs-cis-Glyoxal (CHO−CHO) molecules in excited vibrational states

The microwave spectra of s-cis-glyoxal molecules in the excited states of torsional (v_t=1,2) and bending (v_bend=1) vibrations have been studied. For the v_t=1 state, the rotational constants have been refined and the quartic constants of centrifugal distorition have been determined. For the excited v_t=2 and v_bend=1 states, the rotational constants have found. For the ground vibrational state, the rotational constants and the quartic constants of centrifugal distortion have been refined. The vibrational frequencies have been determined from the relative intensities of rotational transitions. Ufa Scientific Center of Russian Academy of Sciences, Physics Department. Translated fromZhurnal Strukturnoi Khimii, Vol. 36, No. 3, pp.418–423, May–June, 1995. Translated by I. Izvekova     

Calculation of intensities of torsional transitions in vibrational spectra of molecules with internal rotation

Institute of Physiologically Active Substances. Translated from Zhurnal Strukturnoi Khimii, Vol. 31, No. 6, pp. 36–41, November–December, 1990.     

Density functional theory study of vibrational spectra and assignment of fundamental vibrational modes of 1-methyl-4-piperidone

The FT-IR and FT-Raman spectra of 1-methyl-4-piperidone was recorded and the observed bands were interpreted with the aid of normal coordinate analysis following a full structure optimization and force field calculation based on the density functional theory (DFT) using the standard B3LYP/6-311G** method and basis set combinations. A very good agreement obtained between the simulated and experimental spectra was established and unambiguous vibrational assignments of various modes were proposed based on the results of potential energy distribution (PED) calculations.     

Density functional theory study of vibrational spectra, and assignment of fundamental vibrational modes of succinimide and N-bromosuccinimide

This work deals with the vibrational spectroscopy of succinimide and N-bromosuccinimide. The mid and far FTIR and FT-Raman spectra were measured in the condensed state. The fundamental vibrational frequencies and intensity of vibrational bands were evaluated using density functional theory (DFT) using standard B3LYP/6-31G(*) and B3LYP/6-311+G(**) methods and basis set combinations. The vibrational spectra were interpreted, with the aid of normal coordinate analysis based on a scaled quantum mechanical force field. The infrared and Raman spectra were also predicted from the calculated intensities. Comparison of simulated spectra with the experimental spectra provides important information about the ability of the computational method to describe the vibrational modes. Unambiguous vibrational assignment of all the fundamentals were made using the total energy distribution (TED).     

Density functional theory study on molecular structure and vibrational IR spectra of isocytosine

Density functional theory with the combined Becke3-LYP exchange-correlation energy functional [DFT(B3-LYP) method] using the 6-31G(d, p) basis set is applied to predict molecular parameters (geometries, rotational constants, dipole moments) and vibrational IR spectra (harmonic wavenumbers, absolute intensities) of six tautomers of the isocytosine molecule. The results are compared with the corresponding data calculated at the conventional ab initio Hartree-Fock (HF) level using the same basis set and with available experimental data. Calculations show that (a) three amino tautomers are slightly nonplanar species with, evidently, a distorted amino group, (b) the DFT (B3-LYP)/6-31G(d, p) method predicts better molecular parameters, than do the HF calculations, and (c) the DFT(B3-LYP)-calculated vibrational IR spectra of isocytosine agree well with the available recorded IR spectra, and they show marked improvement over the IR spectra predicted at the HF/6-31G(d, p) level. Tautomeric stabilities of isocytosine are discussed on the basis of computed electronic energies by the DFT(B3-LYP) and ab initio approaches [including the MP2 and MP4(SDQ) calculations of electronic energies] and predicted zero-point vibrational energies by DFT(B3-LYP) and HF methods. This relative energies at 0 K of the tautomeric forms of isocytosine predicted by both conventional ab initio and DFT(B3-LYP) methods correlate well with the experimental data, showing the predominance of the aminohydroxy tautomer of isocytosine for an isolated molecule. © 1997 John Wiley & Sons, Inc.     

Density functional theory studies on the electronic and vibrational spectra of octaethylporphyrin diacid

The ground-state structure and electronic and vibrational spectra of octaethylporphyrin diacid (H4OEP2+) have been studied with the density functional theory. The geometrical parameters computed with B3LYP, PBE1PBE and mPW1PW91 functionals and 6-31G* basis sets are well consistent with the experimental values. Electronic absorption spectrum of H4OEP2+ has been studied with the time-dependent DFT method, and the calculated excitation energies and oscillator strengths are compared with the experimental results. The Raman and IR spectra of H4OEP2+ and the Raman spectrum of its N-deuterated analogue (D4OEP2+) were measured. The observed Raman and IR bands have been assigned based on the frequency calculations at the B3LYP/6-31G* level of theory.     

Density functional theory study of vibrational spectra, and assignment of fundamental vibrational modes of 1-bromo 4-fluoronaphthalene

The FTIR and FT-Raman spectra of 1-bromo 4-fluoronaphthalene have been recorded in the regions 4000-100cm(-1) and 3500-100cm(-1), respectively. The spectra were interpreted with the aid of normal coordinate analysis based on DFT (density functional theory) using standard B3LYP/6-311+G** basis set combination for the most optimized geometry. Normal coordinate calculations performed with the DFT force field and subsequently corrected by a recommended set of scale factors, yielded fairly good agreement between observed and calculated frequencies. On the basis of the comparison between calculated and experimental results, assignments of fundamental modes were examined.     

Density functional theory study on the structure and vibrational spectra for cyanuric chloride

The molecular structure and vibrational spectra of cyanuric chloride have been investigated by density functional theory (DFT) using standard B3LYP/6-31G* and B3LYP/6-311+G** method and basis set combinations. The DFT force field transformed to natural internal coordinates was corrected by a well-established set of scale factors that were found to be transferable to the title compound. Both the calculated structural parameters and vibrational frequencies are in good agreement with the available experimental data.     

Correlating the vibrational spectra of structurally related molecules: A spectroscopic measure of similarity

Using catastrophe theory and the concept of a mutation path, an algorithm is developed that leads to the direct correlation of the normal vibrational modes of two structurally related molecules. The mutation path is defined by weighted incremental changes in mass and geometry of the molecules in question, which are successively applied to mutate a molecule into a structurally related molecule and thus continuously converting their normal vibrational spectra from one into the other. Correlation diagrams are generated that accurately relate the normal vibrational modes to each other by utilizing mode‐mode overlap criteria and resolving allowed and avoided crossings of vibrational eigenstates. The limitations of normal mode correlation, however, foster the correlation of local vibrational modes, which offer a novel vibrational measure of similarity. It will be shown how this will open new avenues for chemical studies. © 2017 Wiley Periodicals, Inc.