Dipole moment derivatives and infrared intensities. I. Polar tensors
01 Aug 1974-Journal of Chemical Physics (American Institute of Physics)-Vol. 61, Iss: 3, pp 1040-1049
TL;DR: In this article, the analysis of infrared intensity data to obtain atomic polar tensors is reviewed and slightly reformulated to make it more consistent with nomenclature currently in use for normal coordinate calculations.
Abstract: The analysis of infrared intensity data to obtain atomic ``polar tensors,'' introduced first by Biarge, Herranz, and Morcillo (1961), is reviewed and slightly reformulated to make it more consistent with nomenclature currently in use for normal coordinate calculations. Some properties of these polar tensors are examined, including their relation to the ``effective charges'' introduced by King, Mast, and Blanchette (1972). The procedure is illustrated for formaldehyde and for ethylene to obtain the polar tensors and effective charges for the H, C, and O atoms. A revised set of normal coordinates is used for the latter molecule. The results are compared and discussed.
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TL;DR: Atomic charges were obtained from ab initio molecular orbital calculations using a variety of procedures to compare them and assess their utility, and the ability of the charges to reproduce electrostatic potentials was examined.
Abstract: Atomic charges were obtained from ab initio molecular orbital calculations using a variety of procedures to compare them and assess their utility Two procedures based on the molecular orbitals were examined, the Mulliken population analysis and the Weinhold–Reed Natural Population Analysis Two procedures using the charge density distribution were included; the Hirshfeld procedure and Bader's Atoms in Molecules method Charges also were derived by fitting the electrostatic potential (CHELPG) and making use of the atomic polar tensors (GAPT) The procedures were first examined for basis set independence, and then applied to a group of hydrocarbons The dipole moments for these molecules were computed from the various atomic charges and compared to the total SCF dipole moments This was followed by an examination of a series of substituted methanes, simple hydrides, and a group of typical organic compounds such as carbonyl derivatives, nitriles, and nitro compounds In some cases, the ability of the charges to reproduce electrostatic potentials was examined © John Wiley & Sons, Inc
618 citations
TL;DR: The enthalpy for conformational change from nonplanar to planar EMI+ experimentally obtained by analyzing band intensities of the conformers at varying temperatures is practically the same as that evaluated by theoretical calculations.
Abstract: Raman spectra of liquid 1-ethyl-3-methylimidazolium (EMI+) salts, EMI+BF4-, EMI+PF6-, EMI+CF3SO3-, and EMI+N(CF3SO2)2-, were measured over the frequency range 200−1600 cm-1. In the range 200−500 cm-1, we found five bands originating from the EMI+ ion at 241, 297, 387, 430, and 448 cm-1. However, the 448 cm-1 band could hardly be reproduced by theoretical calculations in terms of a given EMI+ conformer, implying that the band originates from another conformer. This is expected because the EMI+ involves an ethyl group bound to the N atom of the imidazolium ring, and the ethyl group can rotate along the C−N bond to yield conformers. The torsion energy for the rotation was then theoretically calculated. Two local minima with an energy difference of ca. 2 kJ mol-1 were found, suggesting that two conformers are present in equilibrium. Full geometry optimizations followed by normal frequency analyses indicate that the two conformers are those with planar and nonplanar ethyl groups against the imidazolium ring pl...
191 citations
TL;DR: In this paper, the atomic polar tensors of the methyl halide molecules (CH3X) were determined using infrared intensity data reported by Russell, Needham, and Overend.
Abstract: Atomic polar tensors have been determined for H, C, and X atoms of the methyl halide molecules (CH3X), using infrared intensity data reported by Russell, Needham, and Overend. The signs for the ∂p/∂Qi’s have been chosen by considering Coriolis coupling constants, agreement between intensity parameter values for CH3X and CD3X, and by considering the values of the atomic polar tensors calculated by CNDO methods for CH3F and CH3Cl. The resulting atomic polar tensors show systematic trends for the CH3X molecules as X change from F to I. The possibility that atomic polar tensors can be transferred from one molecule to another (with some allowance for expected trends) cannot be ignored. Atomic effective charges for each atom have been calculated, and ξH is found to be nearly constant for the four molecules. Additional properties of the atomic polar tensor are examined, including the anisotropy. A ''modified bond moment hypothesis'' appears to be reasonably successful in modeling the infrared intensities of the methyl halides.
160 citations
TL;DR: In this paper, the infrared intensities for the three fundamental vibrations of the H2O monomer have been analyzed to obtain experimental values for the atomic polar tensors (APTs) for the atoms in the monomer.
Abstract: The infrared intensities for the three fundamental vibrations of the H2O monomer have been analyzed to obtain experimental values for the atomic polar tensors (APTs) for the atoms in the monomer. These APTs have been compared with values calculated for the monomer by an ab initio quantum mechanical treatment using IBMOL‐5 with a 4‐31G basis set. The agreement is satisfactory enough to extend the ab initio calculation to the atoms in the linear water dimer. It is argued that the differences in the APTs from monomer to dimer (and, hence, the intensities for the intramolecular vibrations of the water dimer in terms of the corresponding intensities for the monomer) can be predicted with reasonable certainty by this treatment. The spectrum predicted for the water dimer compares very favorably with the experimental spectrum for the dimer in a N2 matrix, reported by Tursi and Nixon. The calculated APTs for the atoms in the monomer and in the dimer are subjected to a ‘‘charge–charge flux–overlap’’ (CCFO) analysis...
154 citations
TL;DR: It is found that the two solvated isomers can be clearly distinguished by their infrared spectral profile in the 1000-2000 cm(-)(1) range.
Abstract: The density functional theory based molecular dynamics simulation method (“Car−Parrinello”) was applied in a numerical study of the electronic properties, hydrogen bonding, and infrared spectroscopy of the trans and cis isomer of N-methylacetamide in aqueous solution. A detailed analysis of the electronic structure of the solvated molecules, in terms of localized Wannier functions and Born atomic charges, is presented. Two schemes for the computation of the solute infrared absorption spectrum are investigated: In the first method the spectrum is determined by Fourier transforming the time correlation function of the solute dipole as determined from the Wannier function analysis. The second method uses instead the molecular current−current correlation function computed from the Born charges and atomic velocities. The resulting spectral properties of trans- and cis-NMA are carefully compared to each other and to experimental results. We find that the two solvated isomers can be clearly distinguished by the...
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275 citations
TL;DR: In this paper, two rules are presented which relate the intensities of vibrational fundamentals of different isotopic species, analogous to the Teller-Redlich product rule which relates frequencies.
Abstract: Two rules are presented which relate the intensities of vibrational fundamentals of different isotopic species. They are thus analogous to the Teller‐Redlich product rule which relates frequencies. They apply to either infrared or Raman intensities. One rule permits the calculation of dipole‐moment derivatives without the determination of normal coordinates. The application of the rules is illustrated.
274 citations
TL;DR: In this article, carbon-13 frequency shifts for C 2 H 4, C 2 D 4, and as -C 2 H 2 D 2 have been measured in isotopic solid solutions in crystalline films at 60 K.
218 citations
TL;DR: In this article, an analysis of the parallel band of C/sub 2/H/sub 4/ at 2988.66 cm/ sup -1/ was carried out and the inertial constants B and C for each molecule in the ground vibrational state were determined.
Abstract: From an analysis of the parallel band of C/sub 2/H/sub 4/ at 2988.66 cm/ sup -1/ aud the parallel band of C/sub 2/D/sub 4/ at 2201.013 cm/sup -1/ the inertial constants B and C for each molecule in the ground vibrational state were determined as B = 0.9998, C = 0.8294, aud B = 0.7334, C = 0.5636, respectively. From these inertial constants the molecular parameters are deduced to be r/sub CC/ = 1.337 A, r/sub CH/= 1.086 A and < /sub HCH = 177 deg 22'. (auth)
186 citations