Validation of the mPW1PW Quantum chemical calculations for the vibrational study of organic molecules – re‐assignment of the isopropylamine vibrational spectra

The validity of the mPW1PW91 density functional theory (DFT) method coupled to the all‐electron basis set 6‐31G* (mPW1PW/6‐31G*) for the study of amines, using isopropylamine (iPram) as a case study, was evaluated. Validation was performed by comparing the calculated values with the corresponding experimental results obtained and/or reported in the literature. Moreover, the accuracy of that theoretical level was compared with that of other widely used theoretical levels, namely HF/6‐31G*, B3LYP/6‐31G* and MP2/6‐31G*. The effect of basis set improvement within the mPW1PW protocol was evaluated considering the widely used 6‐311G** basis set. On the whole, the results clearly show that the mPW1PW/6‐31G* calculations are a suitable tool for the prediction of the structural and vibrational features of iPram. The validation of the theoretical methodology allowed a complete revision of the vibrational assignments previously reported in the literature, being the result of several proposed re‐assignments. Copyright © 2010 John Wiley & Sons, Ltd.     

Theoretical analysis of vibrational spectra of tautomeric purine forms

A theoretical analysis of vibrational spectra of purine tautomers was carried out using the DFT/B3LYP/6-31G(d)* method. The influence of intermolecular interaction in purine dimers was estimated. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 1, pp. 23–27, January–February, 2008.     

Quantum chemical calculations of vibrational spectra of <Emphasis Type="Italic">para</Emphasis>-ethylbenzenesulfonic acid

Quantum chemical calculations of vibrational spectra of para-ethylbenzenesulfonic acid have been conducted by means of a non-empirical SCF MO LCAO method with the use of the 6-31G(d) basis set. Calculated IR and Raman frequencies are assigned to vibrations of specific atomic groups. It is shown that para-ethylbenzenesulfonic acid can serve as a reasonable quantum chemical model in calculations of vibrational spectra for polystyrene sulfonic resins of various degrees of hydration.     

The vibrational spectra of dibenzofuran

Infrared spectra, polarized along all three orthogonal crystal axes of dibenzofuran, have been recorded from 50 to 3500 cm^?1. The polarized Raman spectra of single crystals have been measured in all possible crystal orientations, and this information has been supplemented by the measurement of depolarization ratios of the Raman lines in solution and melt spectra. This work extends the range of an earlier study carried out before the crystal structure of dibenzofuran was known. With the new data, several changes in the assignment of the molecular fundamentals are necessary; even so, the experimental assignments remain incomplete in many instances. Some lattice modes of the single crystal were observed in the infrared and Raman spectra, and a partial assignment is presented.     

Generalized skeletal approximation in the analysis of vibrational spectra of polymers

A mathematical procedure is given for analyzing the low-frequency region of the vlbrational spectrum for a defective polymer; this reduces the order of the secular equation to the number of degrees of freedom of the atoms forming the skeleton. As a result, the matrices for the kinetic and potential energies become frequency-dependent, and they describe the vibrations of the skeleton at frequencies near zero, with the nodes bearing lumped masses equal to the masses of the repeating units.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 41–47, November, 1978.     

Use of a computer for mathematical analysis of composite vibrational spectra

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 51, No. 3, pp. 523–531, September, 1989.     

Quantum mechanical analysis of resonance Raman spectra of thymine

A direct quantum mechanical calculation of the relative intensities of lines in resonance Raman (RR) spectra of thymine was performed. The method of calculation is based on the adiabatic model in the Herzberg-Teller approximation. It is shown that the basic features of the intensity distribution in the spectra can be explained only by taking into account the vibronic mixing of electronic states and the contribution to the components of the scattering tensor from excited electronic states located close to the resonance state. The calculated results agree satisfactorily with experimental RR spectra of thymine excited by laser radiation at 266, 240, 218, and 200 nm. A comparative analysis of the intensity distribution in the RR spectra of thymine and uracil is carried out.     

Theoretical prediction of vibrational spectra: The out-of-plane force field and vibrational spectra of pyridine

The harmonic force field for the out-of-plane vibrations of pyridine has been calculated from ab initio Hartree-Fock wavefunctions obtained with a 4–21 basis set of contracted Gaussians. To account for systematic errors, the calculated force constants were scaled, using only two independent sclae factors which were transferred unchanged from benzene. The resulting scaled quantum mechanical force field, which is strictly a priori in that it is not based on any experimental data on pyridine, predicts the 64 out-of-plane fundamental frequencies of pyridine and its deuterated isotopomers of C_2v symmetry with a mean deviation from experiment of only 8.5 cm^?1. Addition of polarization functions to the basis set for the nitrogen atom and refinement of the two scale factors by fitting them to the observed pyridine spectra produce no significant improvement in the fit. Assignments of the vibrational spectra are discussed.     

Polarised raman and infrared spectra and vibrational analysis forα-naphthylamine

The Raman spectrum of polycrystalline α-naphthylamine was recorded in the region 100–4000 cm⁻¹. Polarisation measurements were made in CS₂ and CHCl₃ solutions. The infrared spectrum was recorded in nujol mull in the region 200–4000 cm⁻¹. The resolution was better than 2 cm⁻¹ and the accuracy of the measurements was within ± 2 cm⁻¹ for all the spectra. Vibrational assignments have been proposed for the observed frequencies. Out of the 54 normal modes of vibrations, 51 modes could be observed experimentally.     

Quantum chemical interpretation of 13C NMR spectra of adsorbed molecules

In order to assist the interpretation of carbon-13 NMR spectra for molecules sorbed on solid surfaces, a theoretical analysis of resonance shifts was performed which were measured for simple alkenes and arenes in zeolites of type X and Y and on silica gel surfaces. Quantum chemical computations for simple models of adsorption complexes on the basis of CNDO and PCILO methods were combined with resonance shift calculations by means of the Ramsey theory and by employing an empirical formula to find out the most probable structures for the adsorption complexes.     

Davydov splitting of vibrational spectra of adsorbates

A monolayer of adsorbed molecules that form a two-dimensional lattice whose unit cell contains several orientationally nonequivalent molecules is considered. General expressions for the polarizability tensor of this system and the frequencies and integral intensities of s-and p-polarized spectral lines with regard for the electronic polarizability components of the molecules are found. As a result, the discrepancy between the calculated and experimentally observed values of the Davydov splitting for the system CO/NaCl(100) is reduced from 25 to 5%.     

Medium-range structural properties of vitreous germania obtained through first-principles analysis of vibrational spectra

We analyze the principal vibrational spectra of vitreous GeO(2) and derive therefrom structural properties referring to length scales beyond the basic tetrahedral unit. We generate a model structure that yields a neutron structure factor in accord with experiment. The inelastic-neutron, the infrared, and the Raman spectra, calculated within a density-functional approach, also agree with respective experimental spectra. The accord for the Raman spectrum supports a Ge-O-Ge angle distribution centered at 135 degrees. The Raman feature X(2) is found to result from vibrations in three-membered rings, and therefore constitutes a distinctive characteristic of the medium-range structure.