C. Sandorfy

Vacuum ultraviolet and photoelectron spectra of fluoro‐chloro derivatives of methane

The photoelectron and vacuum ultraviolet absorption spectra (200–120 nm) of CF3Cl, CF3Br, CF2HCl, CFH2Cl, CFHCl2, CF2Cl2, and CFCl3 are reported and discussed. The lowest ionization potentials belong to the chlorine or bromine lone pair orbitals, the next highest ones to the bonding orbitals of mainly C–Cl or C–Br character. In the absorption spectra the lowest freuqency bands are due to weak valence‐shell type transitions. At higher freuqencies we find much stronger Rydberg type bands related to the first ionization potential. All absorption bands up to 84 000 cm−1 depart from chlorine or bromine lone pair orbitals. Some of the bands exhibit vibrational fine structure. An increase in the number of the fluorine atoms causes a shift to either higher or lower energies of the ionization potentials belonging to orbitals of mainly C–H or C–Cl character according to the cases while the lone pair ionization potentials and the absorption spectra shift to higher energies in all cases.

THE ELECTRONIC SPECTRA OF n-ALKANES,

Abstract The far ultraviolet absorption spectra of the eight first normal paraffin hydrocarbons were measured down to 1150 angstroms with a MePherson model 225 normal incidence vacuum monochromator completed with a model 665 double beam attachment under approximately 0.2 A resolution. Methane has a diffuse but not entirely structureless band system with a maximum at 1277 A. According to its intensity it should be relating to an allowed transition and must therefore be of the 1 F 2 ← 1 A 1 type. The other seven molecules all seem to have a weak which was predicted by Mulliken in the case of ethane and probably has similar origins in all these molecules. Towards shorter wavelengths strong bands follow. The first strong band system of ethane exhibits a relatively well-resolved vibrational fine structure. The transition is very probably of the 1 E ← 1 A 1 type. The first and second strong bands (and probably the following ones) show a systematic shift toward longer wavelengths and a corresponding increase in intensity. An attempt is made to interpret the spectra in terms of Mullikens united atom treatment of the excited configurations of methane and ethane and of the Pariser- and Parr-type calculations of Katagiri and Sandorfy.

The far-ultraviolet spectra of some simple alcohols and fluoroalcohols

Abstract The vacuum ultraviolet spectra from 2000 to 1200A of methanol, ethanol, n-propanol, iso-propanol and some of their fluorinated derivatives were measured in the gas phase. The spectra are discussed in terms of INDO and, when possible, RCNDO calculations including configuration interaction. The lowest frequency band turns out to be of the σ* - n type. It is followed by two Rydberg transitions, probably overlapping valence-shell transitions.

Anharmonicity and hydrogen bonding: Part III. Examples of strong bonds. General discussion

Abstract The first overtones of some OH and NH stretching vibrations affected by strong hydrogen bonding were measured. The anharmonicity shows a net increase with respect to the related “free” OH and NH vibrations. A general discussion based on the data of the present paper and two previous papers from this laboratory is presented. It is shown that conventional second-order perturbation theory is inadequate in dealing with the anharmonicity of vibrations influenced by hydrogen bonds. Better results are obtained when the off-diagonal terms of the quartic potential constant are included. The posssible effect of higher terms is qualitatively discussed and the relation between anharmonicity and the frequency shift caused by hydrogen bonding is examined. It is concluded that hydrogen bonding has a profound effect on anharmonicity.

Anharmonicity and hydrogen bonding: Part II. Examples of moderately strong OH⋯Y bonds

Abstract Frequencies and, when possible, intensities of the fundamental OH stretching bands and of their first and second overtones were measured for a number of alcohols, phenol, 1,2-propanediol, o-chlorophenol, salicylaldehyde, and orthonitrophenol. It is shown that the mechanical anharmonicity tends to increase for these vibrations as a consequence of medium strong hydrogen bonding. A decrease in mechanical anharmonicity seems to characterize weak hydrogen bonds only.

Comparative study of the vacuum ultraviolet absorption and photoelectron spectra of some simple ethers and thioethers

The vacuum ultraviolet absorption (from 220 to 120 nm) and photoelectron (from 6 to 21 eV) spectra of the following molecules are compared: tetrahydropyran, tetrahydrothiopyran, methylvinylether, methylvinylthioether, dihydropyran, and 4,4‐dimethyl‐2,3‐dihydrothiopyran. The great similarity between the photoelectron spectra of related ethers and thioethers is stressed. In the case of saturated thioethers the corresponding ultraviolet spectra are, however, very different, showing that the involvement of 3d orbitals is important in the low excited states of saturated sulfur compounds. The uv spectrum of tetrahydrothiopyran is interpreted in terms of at least five closely spaced Rydberg series that are of the s, p, or d type. They all converge to the first (S 3p) ionization potential. Both unsaturated ethers and thioethers have one π* ← π band on which s‐, p‐, and d‐type Rydberg series converging to the first (π‐type) IP are superimposed. There is no evidence for the participation of S 3d AOs in the low lyi...

Photoelectron and far‐ultraviolet spectra of CF3Br, CF2BrCl, and CF2Br2

The Hei photoelectron and vacuum ultraviolet spectra up to about 20 eV of CF3Be, CF2Br2, and CF2BrCl have been measured. In both spectra, we find bands at energies lower than in the corresponding chlorine derivatives. Otherwise, the spectra can be interpreted along similar lines. The lowest ionization potentials and the lowest frequency bands in the ultraviolet spectra are due to transitions from the bromine lone pair orbitals.

On the far-ultraviolet spectra of some simple aldehydes

Abstract : The spectra of acetaldehyde, its deuterated homologues, fluoromethyl and chloromethyl derivatives were measured in the ultraviolet down to 85,000/cm in the vapor state. An interpretation is proposed according to which, there are, in this part of the spectrum, three Rydberg transitions due to the lone pair electrons of oxygen which largely overlap, at least three valence-shell transitions. The spectra of thin solid films of some of these compounds were also measured. (Author)

On the general occurrence of the Ham effect in the electronic spectra of aromatic hydrocarbons

Abstract The first singlet-singlet band system of benzene, naphthalene, anthracene, and phenanthrene, was examined at 83°K in solid glasses containing 7% of CCl 3 F, CCl 4 , or C 2 F 4 Br 2 . An intensification of the 0-0 band is observed in all cases where it is symmetry forbidden or weak. It is suggested that the Ham effect offers a means of identifying forbidden band components in the electronic spectra of aromatic molecules. It is also suggested that the perturbation causing the Ham effect is essentially the same for all aromatic hydrocarbons. The near-infrared spectra of benzene and naphthalene were measured at 83°K in a solid glass formed by the 1:1 mixture of CCl 3 F and CF 2 BrCF 2 Br. The spectra show that the molecules are perturbed in their ground state as well as in their excited state.

A Low Temperature Infrared Study of Hydrogen Bonding in N-Alkylacetamides

The infrared spectra of N-methylacetamide and two other secondary amides were measured in solution at temperatures ranging from 22 to −190 °C in both the fundamental and the overtone regions. At least two hydrogen bonded species are found as association increases with decreasing temperature. The effect of hydrogen bond formation on the anharmonicity of the NH stretching vibration and on the NH stretching – NH bending coupling constant is examined.