Dipole Moment Derivatives Research Articles

O−H Stretch Modes of Dodecahedral Water Clusters: A Statistical Ab Initio Study

Infrared frequencies calculations were carried out for 20 (H2O)20 water clusters obeying the 5(12) dodecahedral geometry, optimized at the B3LYP/6-311++G** level. Their combined spectra contained 800 O-H stretch modes, ranging from 2181 to 3867 cm(-1) (unscaled), which were treated and studied as a database. Of these, 752 modes (94%) could be assigned to a single dominant O-H stretch. These 752 were classified into five subdatabases depending on the local H-bond type of the dominant stretch. The frequency (nu) was correlated with the O-H distance (b(OH)), with H-bond length (R(OO)) where applicable, and with other variables. The parameter b(OH) alone accounted for 96-99% of the variance in nu for stretches in H-bonds. The correlation with R(OO) is substantially weaker. Normal modes were classified as "high ratio" or "low ratio" depending upon the mode's distribution of kinetic energy among the O-H bonds. High-ratio modes (389 modes, or 49% of our sample) are modeled well as a single oscillator undergoing small perturbations by weak coupling from other oscillators. Low-ratio modes involve strong coupling with at least one other O-H stretch for which b(OH2) is close to b(OH). The IR intensities of modes vary widely but can be explained in terms of a single equation giving dipole moment derivatives as a function of b(OH). For the lowest-energy (H2O)20 clusters, their IR stretch spectra contained eight distinguishable absorption bands. An explanation for eight bands in terms of the theory of polyhedral water clusters is offered.

Liquid-phase force field and dipole moment derivatives with respect to internal coordinates of benzene

This paper presents an analysis of the infrared vibrational intensities found for C6H6, C6D6 and C6H5D in the liquid phase, motivated in part by the quite marked intensity differences between the fundamentals of C6H6 and C6D6 in the liquid, and between corresponding vibrations in the liquid and gas phases. The analysis is carried out under the harmonic approximation and results from a determination of the force field for liquid C6H6, C6D6 and C6H5D. The force constants for the liquid-phase are presented and compared to those in the literature for the gas-phase. Previously reported experimental intensities are used along with the eigenvectors of the force field analysis to determine the dipole moment derivatives with respect to symmetry and internal coordinates. The dipole moment derivatives with respect to internal coordinates obtained are ∂μ/∂s=0.38±0.02DebyeÅ−1, ∂μ/∂t=0.24±0.01, ∂μ/∂β=0.26±0.01, and ∂μ/∂γ=0.64±0.03DebyeÅ−1. There is very little difference between the dipole moment derivatives with respect to internal coordinates obtained from non-linear least squares fitting of the two D6h isotopomers and those obtained from non-linear least squares fitting of the three isotopomers. The results show that there is significant intensity sharing in the CH stretch region of C6H5D between the fundamental and combination bands.

On the negative dipole moment derivatives of HRgX (Rg=He, Ar, Kr; X=F, Cl) molecules

The large dipole moment and the negative dipole moment derivatives with respect to H–Rg displacement of the neutral HRgX (Rg=He, Ar, Kr; X=F, Cl) molecules have been rationalised by a charge/charge flux/dipole flux decomposition of the charge density using the ChelpG method. This approach was also applied to the hydrogen halides HF and HCl for the sake of comparison. It was found that the dipole moment of HRgX is dominated by the large positive charge contribution while the negative dipole moment derivative of HRgX is due to the dominance of the negative charge flux contribution.

Dipole moment derivatives with respect to the internal coordinates of benzene in the liquid and gas phases

This paper presents a comparison of the dipole moment derivatives with respect to internal coordinates in the liquid and gas phases for benzene-h6, benzene-d6 and benzene-d1. The literature values of the integrated intensities of the infrared active fundamentals of the three gaseous isotopomers are used to determine the dipole moment derivatives with respect to internal coordinates, using the methods described in the previous paper for the liquid phase. As was found for the liquid phase in the previous paper, there is uncertainty surrounding the intensities of the individual CH stretching fundamentals of benzene-d1 due to intensity sharing with active combinations. The magnitudes of the dipole moment derivatives with respect to internal coordinates in the gas phase are ∂μ/∂s=0.50±0.03DÅ−1, ∂μ/∂t=0.28±0.03, ∂μ/∂β=0.24±0.01, and ∂μ/∂γ=0.65±0.02DÅ−1, where s, t, β and γ are the CH stretching, and CC stretching, the HCC bending and the HCCC torsion displacements, respectively. The experimental intensities are different for the three isotopomers in the liquid and gas phases, and the calculations show that these differences are mainly due to a difference between the CH stretch dipole moment derivatives in the two phases. This difference was related qualitatively to the intermolecular interaction of the H with the π-cloud of the nearest neighbour creating a pseudo-hydrogen bond.

Absolute line intensities in methyl bromide: The 7-μm region

This work deals, for the first time, with the modeling of absolute line intensities in the fundamental ν 2 and ν 5 bands of CH 3 79Br and CH 3 81Br at 7 μm. For that, four unapodized absorption spectra of CH 3Br (natural abundance, 99% purity, P × L = 0.082 − 0.165 atm × cm, room temperature) were measured in the range 1260–1560 cm −1, at a resolution of 0.002 cm −1 using a Fourier transform spectrometer Bruker IFS 120 HR. For both isotopomers, 313 line intensities were analyzed within the dyad system required to account properly for the strong Coriolis coupling between ν 2 and ν 5. The intensity fit of experimental data led to the determination of the dipole moment derivatives d 2 = ∂ μ/∂ q 2 and d 5 = ∂ μ/∂ q 5 relative to the ν 2 and ν 5 bands, as well as the first-order Herman–Wallis correction in K to d 5. The observed line intensities are fitted to 3.0% (3.3%) for ν 2 at 1309.9 cm −1 and 2.6% (3.0%) for ν 5 at 1442.9 cm −1, respectively for CH 3 79Br and CH 3 81Br. The values derived for the vibrational band strengths of ν 2 and ν 5 are 55.7(0.6) and 39.2(0.3) cm −2 atm −1 at 296 K, respectively. The corresponding assignments and line positions of the dyad from previous work [F. Kwabia Tchana, I. Kleiner, J. Orphal, N. Lacome, O. Bouba, J. Mol. Spectrosc. 228 (2004) 441] are combined with the present intensity study to provide an improved CH 3Br database for atmospheric applications.

Vibrational assignment and dipole moment derivatives of hexafluorobenzene between 4000 and 250 cm −1

The liquid phase vibrational assignment and dipole moment derivatives of hexafluorobenzene are reported. These are obtained by fitting the imaginary molar polarizability spectrum of hexafluorobenzene to classical damped harmonic oscillator bands. Most of the observed transitions were assigned to infrared active fundamentals or binary combinations. From the active combination transitions, the wavenumbers of the inactive fundamentals were obtained. In addition, ab initio calculations at the CCD/cc-pVDZ level of theory were used to determine the harmonic force field and dipole moment derivatives of gaseous hexafluorobenzene. It was determined that in the gas phase ∂μ y / ∂s 1=−5.53 Debye Å −1, ∂μ x / ∂t 2=1.03, ∂μ x /∂β 1=0.78, and ∂μ z /∂γ 1=0.57 Debye Å −1 while in the liquid ∂μ y / ∂s 1=−4.00 Debye Å −1, ∂μ x / ∂t 2=1.27, and ∂μ x /∂b 1=0.50 Debye Å −1. ∂μ z /∂γ 1 could not be determined for the liquid phase because the fundamental is below the limits of the current measurements. The differences between the liquid and gas phase dipole moment derivatives of hexafluorobenzene were found to be consistent with the differences previously reported for benzene.

Absolute integrated infrared intensities of liquid fluorobenzene between 4000 and 400 cm −1 at 25 °C

This paper is a continuation of the study of the integrated absorption intensities of benzene and its simple derivatives. In this paper, the imaginary molar polarizability spectrum reported earlier for fluorobenzene was fit with 169 classical damped harmonic oscillator bands. The standard deviation and RMSE of the fit are both 0.006 cm 3 mol −1and the area under the fitted spectrum is 0.5% larger than the area under the experimental spectrum. Most of the required peaks are assigned to fundamentals, first overtones or binary combinations. From the parameters of the fitted peaks, the integrated intensities, transition moments and dipole moment derivatives with respect to normal coordinates of the infrared active fundamentals are determined. The F-Sum rule is used to compare the integrated intensities to those of benzene and bromobenzene in the literature. Remarkably, the F-Sums of the out-of-plane vibrations are the same in all the molecules while the in-plane F-Sums vary markedly between the different molecules.

A charge–charge flux–dipole flux decomposition of the dipole moment derivatives and infrared intensities of the AB 3 (A = N, P; B = H, F) molecules

The quantum theory of atoms in molecules (AIM) has been used to decompose dipole moment derivatives and fundamental infrared intensities of the AB 3 (A = N,P; B = H,F) molecules into charge–charge flux–dipole flux (CCFDF) contributions. Calculations were carried out at the MP2(FC)/6-311++G(3d,3p) level. Infrared intensities calculated from the AIM atomic charges and atomic dipoles are within 13.8 km mol −1 of the experimental values not considering the NH 3 and PH 3 stretching vibrations for which the experimental bands are severely overlapped. Group V atomic dipoles are very important in determining the molecular dipole moments of NF 3, PH 3 and PF 3 although the atomic charges account for almost all of the NH 3 molecular moment. Dipole fluxes on the Group V atom are important in determining the stretching band intensities of all molecules whereas they make small contributions to the bending mode intensities. Consideration of dipole flux contributions from the terminal atoms must also be made for accurately describing the intensities of all these molecules. As expected from a simple bond moment model, charge contributions dominate for most of the NH 3, NF 3, and PF 3 dipole moment derivatives and intensities. Charge flux and dipole flux contributions are very substantial for all the PH 3 vibrations, cancelling each other for the stretching modes and reinforcing one another for the bending modes.

Using MD Snapshots in ab Initio and DFT Calculations: OH Vibrations in the First Hydration Shell around Li+(aq)

The average OH stretching vibrational frequency for the water molecules in the first hydration shell around a Li(+) ion in a dilute aqueous solution was calculated by a hybrid molecular dynamics + quantum-mechanical ("MD + QM") approach. Using geometry configurations from a series of snapshots from an MD simulation, the anharmonic, uncoupled OH stretching frequencies were calculated for 100 first-shell OH oscillators at the B3LYP and HF/6-31G(d,p) levels of theory, explicitly including the first shell and the relevant second shell water molecules into charge-embedded supermolecular QM calculations. Infrared intensity-weighting of the density-of-states (DOS) distributions by means of the squared dipole moment derivatives (which vary by a factor of 20 over the OH stretching frequency band at the B3LYP level), changes the downshift from approximately -205 to -275 cm(-1) at the B3LYP level. Explicit inclusion of relevant third-shell water molecules in the supermolecular cluster leads to a further downshift by approximately -30 cm(-1). Our final estimated average downshift is approximately -305 cm(-1). The experimental value lies somewhere in the range between -290 and -420 cm(-1). Also, the absolute nu(OH) frequency is well reproduced in our calculations. "In-liquid" instantaneous correlation curves between nu(OH) and various typical H-bond strength parameters such as R(O...O), R(H...O), the intramolecular OH bond length, and the IR intensity are presented. Some of these correlations are robust and persist also for the rather distorted instantaneous geometries in the liquid; others are less so.

An Atomic Charge−Charge Flux−Dipole Flux Atom-in-Molecule Decomposition for Molecular Dipole-Moment Derivatives and Infrared Fundamental Intensities

The molecular dipole moment and its derivatives are determined from atomic charges, atomic dipoles, and their fluxes obtained from AIM formalism and calculated at the MP2(FC)/6-311++G(3d,3p) level for 16 molecules: 6 diatomic hydrides, CO, HCN, OCS, CO2, CS2, C2H2, C2N2, H2O, H2CO, and CH4. Root-mean-square (rms) errors of 0.052 D and 0.019 e are found for the dipole moments and their derivatives calculated using AIM parameters when compared with those obtained directly from the MP2(FC)/6-311++G(3d,3p) calculations and 0.097 D and 0.049 e when compared to the experimental values. The major deviations occur for the NaH, HF, and H2O molecules. Parallel polar tensor elements for the diatomic and linear polyatomic molecules, except H2, HF, LiH, and NaH, have values resulting from cancellations of substantial contributions from atomic charge fluxes and atomic dipole fluxes. These fluxes have a large negative correlation coefficient, -0.97. IR fundamental intensity sums for CO, HCN, OCS, CO2, CS2, C2H2, C2N2, H2CO, and CH4 calculated using AIM charges, charge fluxes, and atomic dipole fluxes have rms errors of 14.9 km mol(-1) when compared with sums calculated directly from the molecular wave function and 36.2 km mol(-1) relative to experimental values. The classical model proposed here to calculate dipole-moment derivatives is compared with the charge-charge flux-overlap model long used by spectroscopists for interpreting IR vibrational intensities. The utility of the AIM atomic charges and dipoles was illustrated by calculating the forces exerted on molecules by a charged particle. AIM quantities were able to reproduce forces due to a +0.1 e particle over a 3-8-A separation range for the CO and HF molecules in collinear and perpendicular arrangements. These results show that IR intensities do contain information relevant to the study of intermolecular interactions.

Temperature dependence of the optical properties of liquid toluene between 4000 and 400 cm −1 from 30 to 105 °C

This paper presents the first systematic study of the temperature dependence of the optical properties of a liquid. The real and imaginary refractive index spectra, and imaginary molar polarizability spectra of toluene were determined from 30 to 105 °C in 5 °C increments. The peak positions, heights and widths all vary linearly with temperature. However, the broadening of the peak width and lowering of the height are in such a manner that the integrated intensities, transition moments and dipole moment derivatives remain constant. Points in the absorption spectra were observed to be independent of temperature. These points have been labeled isoentosic points.

The infrared vibrational intensities and polar tensors of HFCO and DFCO

The infrared vibrational intensities of HFCO and DFCO have been calculated at the B3LYP/cc-pVTZ, MP2(FC)/6-311++G(3d,3p) and QCISD(FU)/aug-cc-pVTZ levels. All calculations predict the isotopomers to have identical intensity sums, within about 1 km mol −1. This is in contrast with experimental intensity sum results reported in the literature. Dipole moment derivative directions calculated by the three methods are in excellent agreement for all in-plane normal coordinates. All the theoretical polar tensor elements are also in good agreement with each other having standard deviations varying between 0.003 and 0.043 e. The oxygen and fluorine atoms have negative mean derivatives (≈−0.6 e), whereas the carbon mean derivative is very positive (≈+1.1 e) and the hydrogen one is almost zero (≈+0.03 e). The HFCO theoretical intensity sums calculated by all three methods as well as their carbon and oxygen mean dipole moment derivatives are in good agreement with those estimated from the experimental intensities and atomic mean derivatives of H 2CO and F 2CO.

Atomic Mean Dipole Moment Derivative and Anisotropic Contributions to Molecular Infrared Intensity Sums

Atomic anisotropies determined from gas-phase infrared fundamental intensity data for 30 molecules are compared with anisotropies calculated from wave functions obtained with 6-31+G(d,p) and 6-311++G(3d,3p) basis sets at the Hartree−Fock, B3LYP density functional and MP2 electron correlation levels. The discrepancies between the experimental and theoretical anisotropy values are up to 30 times larger than those found for the mean dipole moment derivatives. Although a change in the basis set from 6-31+G(d,p) to 6-311++G(3d,3p) has small effects on the anisotropy values, they are quite sensitive to the inclusion of post-Hartree−Fock electron correlation treatment. Although the calculated results for anisotropies with values <0.7e2 deviate randomly from the experimental results, calculated anisotropies with higher values tend to overestimate the experimental values. Molecules with double bonds (CH2CF2, COH2, COF2, COCl2, cis-C2H2Cl2, CO2, CS2, and OCS) are found to have high atomic anisotropies and large ani...

Differences in the IR Methylene Rocking Bands between the Crystalline Fatty Acids and n-Alkanes: Frequencies, Intensities, and Correlation Splitting

Detailed low-temperature infrared spectra in the methylene rocking−twisting progression band region from 700 to 1000 cm-1 are presented for the C-phase crystalline fatty acids with even numbers of carbons from 16 through 22. There are significant differences between these spectra and those of the corresponding crystalline n-alkanes. The differences in band frequencies, intensities, and splitting are relevant to the interpretation of infrared spectra of complex assemblies of chain molecules such as biomembranes. They are due to chain end and chain-packing differences and can be accounted for using simple models developed in earlier studies, particularly those on the n-alkanes. Band frequency differences result from shifts imposed on the unperturbed frequency by the end groups. Shifts associated specifically with the methyl and acid end groups were estimated from the observed frequencies of the fatty acids, fatty diacids, and n-alkanes and unperturbed frequencies obtained from the dispersion curve for the infinite polymethylene chain. The shifts observed for rocking band frequencies are found to be the sums of the shifts assigned to the end groups. The differences in intensity and intensity distribution can be explained using a model in which the contribution of the individual methylenes to the dipole moment derivative associated with a given band is assumed to be the same except for the terminal methylenes. These methylenes are distinguished by the adjoining chain end group. The intensity differences between a fatty acid and an n-alkane occur because the contribution from the acid-end methylene is much greater than that from the other methylenes. The methylene bands in the spectra of the orthorhombic and monoclinic n-alkanes and C-form fatty acids are split because of interchain vibrational coupling. Their splitting patterns depend on the chain tilt angle. The three different patterns can be accurately reproduced using a simple coupled oscillator model, the different tilts, and three methylene−methylene interchain interaction constants.

Raman and FTIR Spectroscopic Study of LixFePO4 ( 0 ⩽ x ⩽ 1 )

A series of compounds, was prepared by chemical delithiation and investigated with Fourier transform infrared (FTIR) and Raman spectroscopy for the first time. Sample homogeneity with respect to Fe and P was analyzed with an electron microprobe. The imaging capabilities of the electron microprobe reveal larger-sized particles (10-20 μm diam) and fine intergranular particles (⩽1 μm). Elemental analysis with the electron microprobe demonstrates that the particles are relatively homogeneous. Thus, the electron microprobe may be used in conjunction with other instruments that are more commonly used to investigate particle morphology, such as scanning or transmission electron microscopes. Isotopic substitution experiments show that the symmetric and antisymmetric bending vibrations of the anion are highly mixed with translatory vibrations. Consequently, no band in the IR spectrum of may be assigned solely as a lithium ion “cage” mode. Spectroscopic measurements of the series demonstrate that the intramolecular modes of are particularly sensitive to the extraction of ions from and the accompanying oxidation of to Spectroscopic data suggest that the effective force constants (band frequencies), dipole moment derivatives (FTIR intensities), and polarizability derivatives (Raman intensities) change as is converted into Together, the data strongly support the two-phase shell model of delithiation. © 2004 The Electrochemical Society. All rights reserved.

Infrared intensities of liquids XXIV: optical constants of liquid benzene-h 6 at 25 °C extended to 11.5 cm −1 and molar polarizabilities and integrated intensities of benzene-h 6 between 6200 and 11.5 cm −1

We have previously reported accurate absolute infrared intensities of liquid benzene-h 6 between 6225 and 500 cm −1, of liquid benzene-d 6 between 5000 and 450 cm −1, and of liquid benzene-d 1 between 6200 and 500 cm −1. The absolute intensities of benzene-h 6 were reported as spectra and tables of the real refractive index, n, the imaginary refractive index, k, and the molar absorption coefficient, E m, and also as tables of the average areas under, and average peak heights of, bands in the imaginary refractive index and molar absorption coefficient spectra. For benzene-d 6 and benzene-d 1, the absolute intensities were reported as spectra and tables of the real and imaginary refractive indices, and as spectra of the molar absorption coefficient and the imaginary molar polarizability ( α″ m) under the Lorentz local field. Further, the contributions from the different bands to the imaginary molar polarizability spectrum below 5000 cm −1 were separated by fitting the spectrum with Classical Damped Harmonic Oscillator (CDHO) bands. The integrated intensities C j were then obtained from the parameters of the CDHO bands as the areas under the corresponding v ̃ α″ m bands. The integrated intensities gave the transition dipole moments and also, for the fundamentals that are infrared-active in the gas phase, the dipole moment derivatives with respect to the normal coordinates under the double harmonic approximation. The present paper completes the experimental study of benzene-h 6 by presenting the results of the following work. The imaginary refractive index spectrum of C 6H 6 was extended to 11.5 cm −1 from its previous lower limit of 500 cm −1. The real refractive index spectrum between 8000 and 11.5 cm −1 was obtained by Kramers–Kronig transformation of the imaginary refractive index spectrum. It agrees excellently with the real refractive index spectrum directly measured below 100 cm −1, which suggests that the accuracy of the k spectrum is very good, particularly at low wavenumbers. The imaginary molar polarizability spectrum of C 6H 6 between 6200 and 11.5 cm −1 was calculated from the n and k spectra and was fitted with 226 CDHO bands and 1 Gaussian band. No baseline was required in the fit and the baseline absorption was described accurately by the bands used. The integrated intensity, C j,of each band used to fit the spectrum was calculated analytically from the band's parameters. The transition dipole moments were then calculated for the clearly assigned transitions, and the dipole moment derivatives with respect to the normal coordinates were calculated under the double harmonic approximation for the fundamentals that are infrared-active in the gas phase. The values obtained are related to literature values for the liquid and the gas, and are very close to those published previously and compared with the intensities of C 6D 6 and C 6H 5D.

Vibrational infrared intensities and polar tensors of 1,2-difluoroethylenes

The polar tensors of cis and trans-1,2-difluoroethylenes have been determined with new normal modes based in a reassignment of ν 7 and ν 12 bands of the trans isomers and frequency values corrected for Fermi resonances and phase shifts. The signs of the dipole moment derivatives (and its directions, for B u symmetry species) were considered to be those of MP2/6-31G** estimates. Root mean square errors calculated for the new tensor element values from each pair of isotopomers ( trans-1,2-C 2H 2F 2/ trans-1,2-C 2D 2F 2 and cis-1,2-C 2H 2F 2/ cis-1,2-C 2D 2F 2) show that the new polar tensor sets fit the isotopic invariance criterion better than previously reported sets. The accuracy of polar tensor transference procedures was tested by calculating the infrared intensities of trans-1,2-C 2H 2F 2 through the new polar tensors of the cis isomer. The resulting estimates are very accurate and also support the new band assignment, though the A 6 intensity remains still somewhat underestimated.

Density functional calculations of the vibronic structure of electronic absorption spectra.

Calculations of the vibronic structure in electronic spectra of large organic molecules based on density functional methods are presented. The geometries of the excited states are obtained from time-dependent density functional (TDDFT) calculations employing the B3LYP hybrid functional. The vibrational functions and transition dipole moment derivatives are calculated within the harmonic approximation by finite difference of analytical gradients and the transition dipole moment, respectively. Normal mode mixing is taken into account by the Duschinsky transformation. The vibronic structure of strongly dipole-allowed transitions is calculated within the Franck-Condon approximation. Weakly dipole-allowed and dipole-forbidden transitions are treated within the Franck-Condon-Herzberg-Teller and Herzberg-Teller approximation, respectively. The absorption spectra of several organic pi systems (anthracene, pentacene, pyrene, octatetraene, styrene, azulene, phenoxyl) are calculated and compared with experimental data. For dipole-allowed transitions in general a very good agreement between theory and experiment is obtained. This indicates the good quality of the optimized geometries and harmonic force fields. Larger errors are found for the weakly dipole-allowed S0 --> S1 transition of pyrene which can tentatively be assigned to TDDFT errors for the relative energies of excited states close to the target state. The weak bands of azulene and phenoxyl are very well described within the Franck-Condon approximation which can be explained by the large energy gap (>1.2 eV) to higher-lying excited states leading to small vibronic couplings. Once corrections are made for the errors in the theoretical 0-0 transition energies, the TDDFT approach to calculate vibronic structure seems to outperform both widely used ab initio methods based on configuration interaction singles or complete active space self-consistent field wave functions and semiempirical treatments regarding accuracy, applicability, and computational effort. Together with the parallel computer implementations employed, the present approach appears to be a valuable tool for a quantitative description and detailed understanding of electronic excitation processes in large molecules.

Characteristic Substituent-Shift Models for Carbon 1s Ionization Energies and Mean Dipole-Moment Derivatives

Characteristic substituent-shift models for carbon mean dipole-moment derivatives are determined for the halomethanes, fluorochloroethanes, and some other small molecules. These models are analogous to those reported earlier for core ionization energies measured by X-ray photoelectron spectroscopy and are to be expected since Siegbahn's simple potential model relates these to mean dipole-moment derivatives obtained from infrared spectral data. Linear models relating carbon 1s ionization energies and mean dipole-moment derivatives to the number of fluorine, chlorine, bromine, and iodine atoms substituting hydrogen atoms in the halomethanes are reported. The regression coefficients in these models are similar to the coefficients for the fluorine and chlorine atoms found in linear models derived for the mean dipole-moment derivatives and carbon 1s ionization energies of the fluorochloroethanes. The signs of the coefficients in the fluorochloroethane model indicate that the a carbon becames more positive and the β carbon more negative upon fluorine substitution for hydrogen. Standard derivative values of -0.52 ′ 0.05, -0.25 ′ 0.05, -0.18 ′ 0.03, -0.17 ′ 0.03, and -0.01 ′ 0.01 e are proposed for the fluorine, chlorine, bromine, iodine, and hydrogen atoms of saturated fluorochlorohydrocarbons. Characteristic substituent shifts for Mulliken, CHELPG, and Bader charges of the carbon atoms in these molecules are also investigated.

Electric properties of hydrogen iodide: Reexamination of correlation and relativistic effects

The electric dipole moment and the static dipole polarizability of the hydrogen iodide molecule were studied using sophisticated correlated and relativistic methods. Both scalar and spin–orbit relativistic effects were carefully accounted for. We conclude that the large differences between the theoretical and experimental dipole moment, the dipole moment derivative and the polarizability cannot be reconciled by improved account of electron correlation and relativistic effects. The most striking difference between theory and experiment is observed for the polarizability anisotropy. We believe that experimental data, namely the experimental dipole moment (the most recent value is 0.176 au as compared to our best theoretical estimate, 0.154±0.003 au), the parallel polarizability (44.4 and 38.47±0.05 au) and the anisotropy (11.4 and 2.33±0.05 au) must be inaccurate. Experimental and theoretical perpendicular polarizability components (33.0 and 36.14±0.05 au,) and the mean polarizability (36.8 and 36.92±0.05 au) agree better. Our vibrationally corrected relativistic CCSD(T) results represent the most sophisticated predictions of electric properties of HI obtained so far.