A.R.H. Cole

High resolution wavenumber standards for the infrared (Technical Report)

The calibration of high resolution infrared spectra is generally more precise than accurate. This is the case even when they are recorded with Fourier transform interferometers. The present document aims at improving the accuracy of wavenumber measurements in the infrared by recommending a selection of spectral lines as wavenumber standards for absolute calibration in the range from about 4 to about 7000 cm(-1). The uncertainties of these wavenumber standards range from 4+/-1x10(-3) to +/-1x10(-6) cm(-1). Sources of frequency standards, on which the wavenumber determinations are based, are also given.

Vibrational spectra of glyoxal, monodeuteroglyoxal and dideuteroglyoxal

Abstract All i.r.-active vibrations of C2H2O2, C2HDO2 and C2D2O have been studied under resolution sufficient to allow the determination of accurate band centres from the rotational structure. The low frequency torsion v7, which is responsible for the appearance of hot bands, has been investigated in detail and accurate vibrational spacings measured up to the fifth level. The nearly-harmonic character of these spacings is proof that the glyoxal molecule is planar. A Coriolis interaction occurs between the torsion and v12, the antisymmetric skeletal bending vibration.

Solvent effects in infra-red spectra. OE and SH stretching vibrations

Abstract The intensities, band widths and frequencies of the OH stretching vibrations of methanol, tert. -butanol and phenol, and of the SH stretching vibrations of tert. -butyl mercaptan and thiophenol in a range of solvents are reported and discussed in terms of current solvent effect theories. Similar solvent dependences were found for the hydroxyl and thiol solutes in the more strongly bonding solvents suggesting that hydrogen bond forces were operative in both cases. For the hydroxyl compounds, the frequency shifts were found to be related to the electron densities at centres of negative charge on the solvent molecules.

The dipole moment of the CH bond in benzene derivatives from infrared intensities

Abstract Infrared intensity measurements on an out-of-plane CH bending vibration of benzene and fifty methyl- and halo-benzenes lead to a value of 0·64 ± 0·01 D for the dipole moment of the sp 2 CH bond, with indications that the polarity is C − H + . Some anomalously broad absorption bands of n -alkylbenzenes are interpreted in terms of steric interference between the substituent and the ortho-hydrogen atoms.

Rotational fine structure of an infra-red of butadiene and the length of the central CC bond

Abstract The rotational fine structure of the type- C band of butadiene at 908 cm −1 has been recorded under considerably higher resolution than previously the Q structure fully resolved from hot bands arising from molecules in excited levels of the torsional mode. The analysis as an approximate symmetric top gives A″ — B″ = 1·245 ± 0·002 cm −1 which with the accurate B″ value of 0·1413 ± 0·0002 cm −1 determined by M arais et al . by Raman spectroscopy and a number of plausible assumptions leads to values of r (CC) = 1·464 ± 0·003 A and ∠(CCC) = 123·2 ± 0·2°. The central carbon—carbon bond length is significantly shorter than that obtained earlier by electron diffraction and is now consistent with the distance of C sp2 C sp2 distance of cyclo -octatetraene.

Solvent effects on the infra-red frequency and intensity of the nitrile vibration in aceto-, propio-, benzo- and phthalo-nitriles

The nitrile frequency displacements relative to the vapour are substantial but almost independent of solvent. The intensities are conversely very solvent-dependent, those in chloroform being for example over twice those in isooctane. Neither effect is explained by current theoretical treatments. The authors suggest that the high local field of the CN group may modify solvent properties. The CN intensity in the aromatic nitriles is greater than in the aliphatic, and the intensity ratio between benzo- and phthalonitrile is accounted for by the Hammett σ-factor. The empirical solvent sequence found by Archibald and Pullin for CO frequencies is also valid for CN intensities, which when plotted solvent by solvent correlate linearly with each other and also with CO frequencies. The same correlation exists approximately for CN frequencies.

Solvent effects on out-of-plane CH bending absorption of benzene derivatives

Abstract Infrared frequency and intensity measurements on a CH out-of-plane bending mode of benzene and some of its derivatives dissolved in solvents of different polarity have been used to test theories of solvent effects. None of the equations involving solvent dielectric constant and/or refractive index is capable of predicting accurately the observed effects.

The energy of a hydrogen bond by infra-red spectroscopy

Abstract Intensity measurements at different temperatures on the hydroxyl stretching absorption band are used to determine the energy of the hydrogen bond formed between a substituted cyclo hexanol ( trans -dihydrocryptol) and a cyclic ether (dioxan) in tetrachloroethylene solutions. Allowance is made for the temperature variation of the intensity of non-bonded hydroxyl groups and the hydrogen bond energy found is 3·2 ± 0·3 kcal/mole.

Water vapour spectra for the calibration of infrared spectrometers

Abstract An improved set of diagrams and tables is presented to augment those in the IUPAC Tables of Wavenumbers for the Calibration of Infrared Spectrometers.