C.A. McDowell

X-ray photoelectron spectroscopy of copper compounds

The X-ray photoelectron spectra of some forty-six copper compounds and complexes have been measured. The chemical shifts obtained from accurate determinations of the binding energies have been qualitatively explained on the basis of the Pauling electronegativity concept using the group electronegatives of Huheey for the polyatomic counter anions. The chemical shifts of the copper atoms as well as the atoms in the ligands were found to be dependent not only on the oxidation state but also on the kind and number of ligand atoms. Intense satellite lines were found in the 2p and 2s bands of the cupric compounds; the number and splitting of the satellites were found to be sensitive to the chemical environment. A correlation was found between the satellite splitting and the binding energies and this is explained by a 3d→4s, 4p ‘shake-up’ mechanism.

Photoelectron Spectra of the Halogens

Photoelectron spectra of valence shell electrons in F2, Cl2, Br2, and I2 yield information on the molecular and electronic structure of the lowest several states of the corresponding positive ions, some of which is not available from previous spectroscopic studies. Spin–orbit fine structure is resolved for the ground 2Πg states of F2+ and Cl2+; values obtained are ζ = 337 ± 40 and 645 ± 40 cm−1, respectively. The first excited states of the ions are identified as 2Πu and approximate values of ζ = 2000–2200 and 6400 cm−1 obtained for Br2+ (A 2Πu) and I2+(A 2Πu), respectively. A state in F2+ reported previously [D. C. Frost, C. A. McDowell, and D. A. Vroom, J. Chem. Phys. 46, 4255 (1967)] to lie at ∼ 17.4 eV is not observed here and is attributed to nitrogen impurity. Vibrational frequencies for F2+ and Cl2+(X 2Πg) are in agreement with spectroscopic work. The corresponding frequencies for Br2+ and I2+ are ωe = 360 ± 40 and ∼ 220 cm−1. A change in bond length to Br2+(2Πg) of Δre ∼ (−)0.095 A is estimated fr...

X-ray photoelectron spectra of cobalt compounds

The X-ray photoelectron spectra of a variety of cobalt(II) and cobalt(III) complexes have been investigated. Intense satellite lines were observed for the 2p, 3s and 3p peaks in the case of the high spin cobalt(II) compounds, but not for low spin cobalt(III) complexes. The satellites of the 2p levels are best explained as arising from shake-up processes, whereas those of the 3s and 3p levels are thought to arise largely from multiplet (exchange) splitting of the levels. Multiplet splitting of the 2p level is small and responsible for an increase in the doublet separation of the 2p1/2, 2p3/2 spin-orbit levels of the high spin cobalt(II) compounds. The chemical shifts for cobalt differ for the 2p, 3s and 3p levels of the high spin cobalt(II) compounds. Those of the 2p and 3p levels of diamagnetic cobalt(III) and low spin cobalt(II) complexes are equal. The difference in the case of the high spin cobalt(II) compounds is thought to be due to the presence of unpaired 3d electrons.

High resolution solid state 13C NMR spectra of carbons bonded to nitrogen in a sample spinning at the magic angle

High resolution solid state 13C NMR spectra of amino acids and nitrile compounds have been obtained by a combination of cross‐polarization, dipolar decoupling, and magic angle spinning techniques (CP–MAS). The resonances of Cα and cyano carbons in the observed 13C spectra show asymmetric doublet patterns. This problem has been treated by using the adiabatic approximation since the 14N quadrupole interaction is much larger than the spinning frequency. Theoretical spectra have been simulated for these carbons and they show very good agreement with experimental observations.

Chemical shielding tensor and 13C–14N dipolar splitting in single crystals of L‐alanine

Chemical shielding tensors have been determined for three chemically distinct carbons in a single crystal of L‐alanine using proton‐enhanced 13C NMR. The results indicate that the most shielded direction is perpendicular to the sp2 plane for the carboxyl carbon and the C3 axis for the methyl carbon. 13C–14N dipolar splittings have been observed for the Ca carbon, causing further complication in spectral analysis. Since the 14N quadrupole coupling constant is of comparable order with the 14N Zeeman interaction, 14N quadrupole interaction is effective in the 13C–14N dipolar splittings. The 14N quadrupole effect is observed and demonstrated by calculation and the sign of the quadrupole coupling constant e2Qq has been determined to be positive. The chemical shielding tensor for the Ca carbon is determined by considering the 13C–14N dipolar interaction and the 14N quadrupole interaction. It is shown that the 14N quadrupole interaction causes the asymmetric doublet pattern in the 13C NMR signal for the Ca carbo...

14N quadrupole effects in CP-MAS 13C NMR spectra of organic compounds in the solid state

Abstract The high-resolution solid-state 13 C NMR spectra of 2,6-dimethyl-3-nitroaniline, glycylglycine, glycyl- l -alanine, and trimethylimidazole, were obtained by a combination of cross-polarization and magic-angle spinning techniques (CP-MAS). The 13 C NMR lines of the carbon atoms bonded to nitrogen in these compounds showed a characteristic line broadening or asymmetric doublet patterns. The theoretical lineshapes of the 13 C NMR lines arising from the carbon atoms bonded to nitrogen were calculated using the adiabatic approximation since the rate of change of the Zeeman-quadrupole Hamiltonian of nitrogen nucleus is very slow when compared to the speed of the spinning sample holder in the MAS experiment. In the calculation, an asymmetric quadrupole coupling tensor of nitrogen nucleus was considered. It was found that the calculated lineshapes are in good agreement with the experimentally observed lineshapes, and that the 14 N quadrupole coupling tensor was responsible for the lineshapes of the carbon atoms bonded to nitrogen. The sign of the quadrupole coupling constants of the nitro and amino nitrogens in 2,6-dimethyl-3-nitroaniline were determined to be negative from an analysis of the lineshapes. In the case of trimethylimidazole, it was found that the 13 C NMR signals of the C 4 and C 5 carbon atoms could also be assigned from a comparison of the theoretical and experimental lineshapes. This resolution of the C 4 and C 5 NMR resonances was possible because of the freezing-out of the tautomerism involving the NH bonds.

Evidence for multiplet splitting of 2p photoelectron lines of transition metal complexes

Abstract Differences in the 2p 1 2 –2p 3 2 energy separation have been observed between diamagnetic and paramagnetic transition metal ion complexes. These differences are interpreted in terms of the exchange splitting of the lines by the unpaired valence electrons in the case of the paramagnetic complexes.

A “magic echo” pulse sequence for the high-resolution NMR spectra of abundant spins in solids

Abstract We describe a new pulse sequence involving two time-reversal spin echoes (TREV) for the high-resolution NMR of abundant spins in solids. It is shown that for a cycle time longer than T 2 . TREV is apparently superior to the MREV-8 pulse sequence.

The photoelectron spectrum of HCP and comments on the first photoelectron band of HCN

Abstract The photoelectron spectrum of HCP has been obtained, Ionization potentials are found at 10.79 ± 0.01 eV (X 2 Π) and 12.86 ± 0.01 eV (A 2 Σ). By comparison with HCP, a new interpretation of the first photoelectron band of HCN has been proposed which involves a Renner-Teller interaction in the Σ + vibronic states of the molecular ion.

Valence‐Shell Ionization Potentials of Halomethanes by Photoelectron Spectroscopy. I CH3Cl, CH3Br, CH3I. Vibrational Frequencies and Vibronic Interaction in CH3Br+ and CH3Cl+

Photoelectron spectra of methyl chloride, methyl bromide, and methyl iodide obtained with 584‐A radiation yield in each case four of the five valence‐shell ionization potentials. Values of 11.29, 10.53, and 9.50 eV are obtained for the first ionization potentials, respectively, corresponding to ionization from halogen “lone‐pair” orbitals. Resolved vibrational structure allows determination of frequencies of the corresponding normal vibrations of the positive ions in several cases. Relative intensities of vibrational components in the first ionization potential are dictated by vibronic interaction. Approximate values of the Jahn–Teller parameters D for ν4, ν5, ν6 in CH3Br+ may be obtained from these intensities. Small values of D (D ≤ 0.1) suffice to produce sizeable modifications of intensity for the intermediate spin–orbit splittings observed in these ions.