Infrared Absorption Intensities Research Articles

A b i n i t i o (STO-3G) dipole moment derivative properties of the CHn series

The atomic and bond dipole moment derivative properties associated with the total infrared absorption intensity of the methylidyne, methylene, and methyl free radicals, and of methane, have been calculated by means of the ab initio STO-3G algorithm. These properties include the coordinate-dependent atomic polar tensors and the following invariant quantities: the dipole derivatives for a bond stretch, mean atomic dipole moment derivatives, atomic anisotropies, and the effective atomic charges. Three sets of calculations were conducted for each species by combining the experimental or theoretically determined equilibrium molecular geometry with the standard or optimum orbital exponent scaling factors. The relationship between each of these dipole derivative properties and, in turn, the equilibrium geometry, the carbon and hydrogen scaling factors, and the number of bonded hydrogen atoms is analyzed. According to any calculation, it is found that the calculated dipole derivative value for a C–H stretch in methane is negative, which agrees with the experimentally deduced results, but is positive for all the radicals, except the doublet state of CH. Furthermore, it is shown that the optimum scaling factors must be used in the calculations in order to consistently obtain good agreement between theory and experiment. Based on both the theoretical equilibrium geometry and the optimum scaling factors of a species, the following trends are exhibited by this homologous series of hydrocarbons: (1) The dipole derivative magnitude for a C–H bond stretch is a monotonic increasing function of the product of the carbon and hydrogen scaling factors. (2) The effective charge of carbon increases as the optimum size of the carbon valence shell increases, and decreases as additional hydrogens are bonded to the carbon. (3) The hydrogen effective charge generally decreases as the number of hydrogens increases. (4) The mean dipole derivative of hydrogen is a monotonic decreasing function of the number of C–H bonds, and is negative only for methane. (5) Calculations on the doublet and quartet electronic states of CH yield different values for the dipole moment, the effective charge, and the anisotropy, the dipole derivatives for a bond stretch have opposite directions.

Absolute Intensity Measurement of the ν4 Band of Fluoroform by the Use of a Tunable Diode-laser Source

Abstract The absolute infrared absorption intensities have been measured for the P35(35) and P36(36) lines, which belong to the ν4 fundamental of fluoroform, by the use of a tunable diode-laser source. The observed intensity, Γ, was 5360+220 cm2 mol−1. This intensity value was compared with that observed by the conventional method.

ChemInform Abstract: INFRARED BAND INTENSITIES OF ETHYLENE OXIDE

The infrared absorption intensities of ethylene oxide and ethylene oxide‐d4 were measured in the gas phase using the pressure broadening method. When a band is overlapped by other bands, it is separated by the simulation calculation. The obtained band intensities were analyzed by the least squares method with the aid of the results from the Coriolis analyses and the CNDO/2 calculations. The correct sign combination of (∂p/∂Qi) has been sucessfully determined. The atomic polar tensors and the local intensity parameters of the CH2 group were calculated. The CH2 local intensity parameters of ethylene oxide were found almost equal to those of cyclopropane, and different from those of C–CH2–C and CH2 = C systems.

Dynamical and optical properties of the ethylene crystal: Self-consistent phonon calculations using an ‘‘a b i n i t i o’’ intermolecular potential

Using an intermolecular potential from ab initio calculations, we have calculated the structure and solved the lattice dynamics problem of the ethylene crystal in the self-consistent phonon formalism. The anharmonic effects, as included by this formalism, systematically improve the optical mode frequencies, in comparison with experiment, but the corrections to the harmonic frequencies are still substantially too small. The crystal structure and its pressure dependence are well represented. From the phonon polarization vectors we have also evaluated the Raman scattering and infrared absorption intensities of the optical modes, applying a scheme which takes into account the mutual polarization of the molecules (the ’’local field corrections’’). The Raman intensities agree quite well with experiment; the infrared intensities are less realistic, probably due to the neglect of intermolecular overlap effects in the intensity calculations. Using an empirical atom–atom potential for hydrocarbons instead of the ab initio potential, the assignment of the optical lattice modes by their calculated frequencies was not fully consistent with the Raman intensity ratios obtained from their polarization vectors.

Unified theory of the dielectric properties and lattice vibrational intensities of the HCN crystal

The effective polarizability of the HCN molecule in its two crystal phases is calculated from the mean crystal dielectric constant and molecular- orbital dipole moment calculations, using lattice dipole sums for molecules treated as one, two and three points. The axial polarizability agrees with the gas-phase value, but the transverse polarizability from each calculation is roughly twice the gas-phase value. The lattice infrared absorption intensities and LO-TO splitting are calculated; the three-point treatment with the crystal-phase polarizability yields agreement with experiment. The lattice Raman intensities are also calculated; they depend markedly on the choice of polarizability. The results illustrate how several properties can be calculated within one model. Some inconsistencies for HCN may be attributable to the effects of hydrogen bonding, but could be resolved by dielectric tensor, refractive index, or lattice Raman intensity measurements.

Infrared band intensities of ethylene oxide

The infrared absorption intensities of ethylene oxide and ethylene oxide-d4 were measured in the gas phase using the pressure broadening method. When a band is overlapped by other bands, it is separated by the simulation calculation. The obtained band intensities were analyzed by the least squares method with the aid of the results from the Coriolis analyses and the CNDO/2 calculations. The correct sign combination of (∂p/∂Qi) has been sucessfully determined. The atomic polar tensors and the local intensity parameters of the CH2 group were calculated. The CH2 local intensity parameters of ethylene oxide were found almost equal to those of cyclopropane, and different from those of C–CH2–C and CH2 = C systems.

芳香族ニトロ化合物のニトロ基対称および逆対称伸縮振動の赤外吸収強度

Infrared absorption intensities of the NO2 symmetric and antisymmetric stretching vibrations were measured for some aromatic nitrocompounds. It was shown that in the case of ortho alkyl-substituted nitrobenzenes, the intensities of the symmetric stretching vibration decrease in an orderly fashion when the degrees of the twisting of NO2 group from the plane of benzene ring increase owing to the ortho effect, while the quite opposite behaviour is observed for the antisymmetric stretching. From these results, it was concluded that the factor determining the intensities in question is the conjugation effect between NO2 group and benzene ring. This was confirmed by the fact that in the case of para substituted nitrobenzenes, completely the same tendencies were observed in relation to the changes in the conjugation effect according to the kinds of substituents. Finally, it was shown that the sum of the intensities of the two vibrations is approximately constant for the compounds treated here, except those containing very strong electron-donating groups such as NH2 and N (CH3) 2.

Infrared intensities of the fundamental vibrations of liquid H 2O

Infrared absorption intensities of the fundamental vibrations of liquid H 2O have been obtained by measuring transmissions at two sample thicknesses (about 9 and 0.9 μ). The effect of multiple internal reflections on the observed absorptions is examined in terms of thin-film optics. It is shown that this simple method yields precise absorption intensities, without corrections for the effects of multiple internal reflections. The resulting intensities are 89.9 × 10 3 cm/mmol and 5.91 × 10 3 cm/mmol for the stretching and bending vibrations, respectively. The latter value was estimated after eliminating the absorption of intermolecular vibrations from the 1400–2400 cm -1 region by means of computer simulation.

Finite field method calculations. VI. Raman scatering activities, infrared absorption intensities and higher-order moments: SCF and CI calculations for the isotopic derivatives of H2O and SCF calculations for CH4

Finite-field perturbation methods are applied in calculating polarisabilities and polarisability gradients at the CI level for H2O, D2O, T2O, HDO, HTO and DTO. Dipole moments and dipole moment gradients are also calculated. The resulting Raman scattering activities and infrared absorption intensities are derived and compared with the SCF results in part V along with other theoretical and experimental values. Higher-order moments and polarisability tensor components are calculated for H2O at the SCF and CI levels and for CH4 at the SCF level. The calculated values are compared with the results of other calculations as well as the currently available experimental values.

Enthalpy difference of rotational isomers in liquid butane and pentane from infrared spectra

In the course of a study of the absolute infrared absorption intensities of the fundamentals of liquid normal alkanes at different temperatures, the authors derived the enthalpy difference between the conformational isomers of liquid butane and pentane.(AIP)

Quantitative Infrared Absorption Measurements on Tri-n-Butyl Phosphate

The molar absorptivity, ε(ν̄) of three intense infrared absorption bands in tri- n-butyl phosphate has been measured as a function of concentration. For all three bands, ε(ν̄) is independent of concentration for dilute solutions, then decreases uniformly with increasing concentration, and finally becomes independent of concentration again as one approaches the pure liquid. A saturation effect is found at about 1.0 M for all cases. Deviations from Beer's law behavior are observed at concentrations which depend upon the absorption band and/or the choice of nonpolar solvent. Self-association of the solute molecules is considered to be the cause of the decrease in ε(ν̄) with increasing concentration. From the measured data, it is possible to estimate the number of solvent molecules required to prevent this self-association. For CCl4, we find this value to be 25 molecules of solvent per solute molecule, a value in agreement with elementary geometric consideration.

Infrared photochemistry of ethylene clusters

Infrared irradiation of ethylene clusters formed in supersonic molecular beams, using a low power cw CO2 laser, results in the photodissociation of a large fraction of the van der Waals molecules. Under such conditions, infrared absorption intensity exhibits first-order power dependence and is readily detected as loss in molecular beam intensity. Intramolecular energy transfer rates, determined by measuring spectral linewidths, are shown to vary with the vibrational mode initially excited. Ethulene clsuters containing one quantum of vibrational energy corresponding to the νn7 fundamental in the monomer (949 cm−1) have a vibrationally predissociative lifetime of 0.33 psec. In comparison, the relaxation rate of ethulene-d4 clusters with one quantum of exctation corresponding to the ν12 (1078 cm−1) mode of C2D4 is 0.7 psec.

ChemInform Abstract: INFRARED ABSORPTION INTENSITIES OF ALLENE

Chemischer InformationsdienstVolume 11, Issue 2 Physical Organic Chemistry ChemInform Abstract: INFRARED ABSORPTION INTENSITIES OF ALLENE Y. KOGA, Y. KOGASearch for more papers by this authorS. KONDO, S. KONDOSearch for more papers by this authorT. NAKANAGA, T. NAKANAGASearch for more papers by this authorS. SAEKI, S. SAEKISearch for more papers by this author Y. KOGA, Y. KOGASearch for more papers by this authorS. KONDO, S. KONDOSearch for more papers by this authorT. NAKANAGA, T. NAKANAGASearch for more papers by this authorS. SAEKI, S. SAEKISearch for more papers by this author First published: January 15, 1980 https://doi.org/10.1002/chin.198002049AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume11, Issue2January 15, 1980 RelatedInformation

Infrared absorption intensities of allene

The infrared absorption intensities of the fundamental bands of CH2=C=CH2 and CD2=C=CD2 were measured in the gas phase. The Coriolis interaction between ν7 and ν10 bands of CD2=C=CD2 was analyzed to obtain information about the signs of (∂p/∂Qi). The perturbation was found to be positive. Utilizing the obtained data, the correct sign combination was determined. The polar tensors and the atomic effective charges as well as the local intensity parameters have been obtained using the determined sign combination of (∂p/∂Qi). The results were discussed in connection with the empirical rules for the signs of CH bond stretching and bending motions. Predictions of this rule were found to be well satisfied in this molecule.

Finite field method calculations. V. Raman scattering activities and infrared absorption intensities for H 2O, D 2O, CH 4 and CD 4

Finite-field perturbation methods are applied in calculating polarisabilities, polarisability gradients, dipole moments and dipole moment gradients at the SCF level for H 2O, D 2O, CH 4 and CD 4. The corresponding Raman scattering activities and infrared absorption intensities are calculated and compared with experimental and other theoretical determinations.

Infrared absorption intensities of methyl acetylene

The infrared absorption intensities of the fundamental bands of CH3CCH, CD3CCH and CH3CCD were measured in the gas phase by the pressure broadening technique. Out of 32 possible sign combinations of (∂p/∂Qi) for each of a1 and e species, only one combination was selected for both species, utilizing the isotopic data, Coriolis information, and the CNDO calculation. Thus, the polar tensor and the effective charges were obtained, as well as the dipole moment derivatives with respect to primitive coordinates. Comparison of these parameter values with those of other molecules suggests that the methyl hydrogens in methyl acetylene resemble those in methyl halides rather than those in saturated hydrocarbons, while the acetylenic hydrogen seems to retain the property in acetylene molecule itself. On the other hand, the CNDO method was not found very successful in this molecule as in propane, cyclopropane, or benzene. In particular, its capability to predict intensity parameter values concerned with the acetylenic group of this molecule was found fairly poor.

Absolute infrared intensities of cyclopropane-d and cyclopropane-d6: Dipole moment derivatives and polar tensors

Integrated infrared absorption intensities for the fundamental vibrations of gas-phase cyclopropane-d0 and cyclopropane-d6 were experimentally determined using nitrogen pressure-broadening techniques. Although the experimental data are insufficient to resolve the relative sign combinations for the (∂P/∂Qi) and (∂P/∂Sj) charge distribution parameters in the A2′′ symmetry species, a definitive relative sign choice is indicated for the E′ dipole moment gradients. The normal coordinate transformations required for the dipole derivative analysis are based on the highly reliable force field derived by Duncan and Burns [J. Mol. Spectrosc. 30, 253 (1969)]. For ease both in computing the atomic polar tensor elements of cyclopropane and in comparing cyclopropane force constants and dipole derivatives to related systems, the Duncan and Burns potential function is recast in terms of a set of more convenient internal valence force constants. (∂P/∂Qii) dipole gradients determined by semiempirical CNDO/2 molecular orbital calculations are used to indicate a preferred sign for the dipole derivatives. Atomic polar tensors for the carbon and hydrogen atoms of cyclopropane are calculated and compared to those for methane and ethylene. The effective charge parameter for the hydrogen atom in cyclopropane is also discussed.

Absolute Intensity Measurement of Infrared Absorption by the Use of CO2 Laser Source

Abstract The absolute infrared absorption intensities have been measured for the QR0(0) line (ν3 fundamental) of methyl fluoride and the RR8(9) line (ν6 fundamental) of methyl iodide by the use of CO2 laser lines of P(16) and P(8), respectively. The observed intensities, Γ, were: 12500±4300 cm2·mol−1 for the ν3 band of methyl fluoride and 1040±40 cm2·mol−1 for the ν6 band of methyl iodide.

Isotope effect on the zero point energy shift upon condensation. I. Formulation and application to ethylene, methane, and fluoromethanes

A method of evaluating the isotope effect (IE) on the zero point energy (ZPE) shift upon condensation due to the London dispersion forces in the liquid has been formulated. It is expressed to the first order, as a product of an isotope-independent liquid factor and a factor of isotopic differences in gas-phase properties. The theory has been tested by calculating the effective atomic charges for carbon and hydrogen in ethylene, according to the CNDO/2 molecular orbital algorithm, and it correctly predicts the magnitude of the IE on the ZPE shift and the first-order sum rules involving the isotopic ethylenes. However, it fails to explain the difference in vapor pressures of isotopic isomers. The theory has also been applied to the D/H and to the 13C/12C isotope effects in methane and fluoromethanes. The results obtained from the CNDO/2 calculations have been compared with the experimental values of the total infrared absorption intensities and of the IE on the ZPE shift of isotopic methanes. Based on these calculations, the molecular properties that enhance the stronger dispersion forces in the liquid phase between the lighter molecules than between the isotopically heavier molecules, and hence favor a large IE on the ZPE shift, have been deduced.

Infrared absorption intensities of formyl fluoride

The i.r. absorption intensities of gaseous HCOF and DCOF have been measured under high pressure. The intensity analysis has been carried out, and the derivatives of molecular dipole-moment with respect to a bond stretching or a valence angle deformation have been determined as intensity vectors by the least squares method. Assuming the directions of intensity vectors are those calculated by the CNDO/2 or INDO method, their magnitudes have been determined as follows: a CH = − 0.22, a CO = − 2.90 and a CF = − 5.02( D/Å). Above values are close to those of intensity vectors of unsaturated fluorocarbons. The effect of π electrons on the intensity vectors is briefly discussed.