Specific Molecular Orbitals Research Articles

Tuning Spin-State Preference by Substituents: A Case Study of Thianthrene Dication

We report an effective example of π-conjugated systems showing the reverse spin-state preferences depending on the substitution patterns. It is shown that 2,3,7,8- and 1,4,6,9-tetramethoxy-substituted thianthrenes have different electronic structures owing to destabilization of the specific frontier molecular orbitals. On the basis of the hybrid Hartree−Fock/density functional method (B3LYP/6-31G*), the singlet−triplet energy gaps are estimated to be −10.7 and +8.8 kcal/mol for 2,3,7,8- and 1,4,6,9-substituted thianthrenes, respectively. Moreover, it is also shown that nuclear independent chemical shift (NICS), the index of local aromaticity for polycyclic π-conjugated systems, is closely correlated with the spin-state preferences of the present thianthrene system.

Sputtering of organic molecular monolayers self-assembled onto Ag(1 1 1) and Au(1 1 1) surfaces

Metastable-induced electron spectroscopy (MIES), X-ray and UV photoelectron spectroscopies (UPS) were employed to study sputtering kinetics of monolayers of hexadecanethiol (HDT) molecules, CH 3(CH 2) 15SH, self-assembled on Au(1 1 1) and Ag(1 1 1) substrates under 800 eV He +-ion bombardment in the dose range up to 1.3×10 16 cm –2. A distinct low-level damage stage extending up to a dose of about 8×10 13 cm –2 could be distinguished in sputtering kinetics of the HDT/Ag system. The bands of enhanced electron emission from specific molecular orbitals arising in the difference MIES and UPS spectra and evolving in the course of ion irradiation of HDT/Ag and HDT/Au were identified by juxtaposing with the spectra of hexadecane and octadiene. In both systems, ion bombardment was found to induce the formation of CC double bonds. The character of sputtering kinetics depends on the substrate. The HDT/Au system is characterized by a considerably higher rate of destruction of the film, with the initial sputtering yield being nearly twice as great as that for HDT/Ag.

A photoelectron study of the inner valence molecular orbitals of N 2O

Photoelectron spectra are reported for the inner and outer valence regions of N#2#O for several photon energies up to 120 eV. The outer valence region is characterized by four well resolved bands which can be assigned to ionisation from specific molecular orbitals. In contrast, the inner valence region displays a complex structure, composed of many overlapping lines, extending to a binding energy of approximately 45 eV. The experimental data are compared with theoretical calculations and with a spectrum recorded using X-ray excitation. Several of the features observed in the inner valence region can be interpreted with the aid of theoretical predictions.

The Photoelectronspectra of Halogen Substituted Glyoxals

Abstract The photoelectronspectra of three symmetrical single(E)-oxalyl dihalides (X=F,Cl,Br) have been measured. The ionisation potentials between 8–16 eV have been determined and assigned to specific molecular orbitals. The spectra have been interpreted by a simple localized molecular orbital model including spin-orbit coupling. The assignments have been compared with the results of an iterative extended Huckel MO-calculation and the SCF-MO calculations of Frost1.

The photoelectron spectra of amides, thioamides, ureas and thioureas

The photoelectron spectra of some amides, thioamides, ureas and thioureas have been measured over the range 7—20 eV. Ionisation potentials have been determined and in some cases associated with ionisation processes from specific molecular orbitals. Some of the energy levels in related molecules have been correlated, and values of the lowest ionisation potentials have been considered in relation to the formation of intermolecular complexes.

Photoelectron spectra of vinyl and allyl halides

Photoelectron spectra of vinyl halides, vinyl methyl ether, allyl halides and allyl alcohol have been measured in. the range 6–21 eV. Ionization potentials have been determined for each molecule, and assigned in some cases to specific molecular orbitals. Vibrational structure has been found with some of the bands. In the case of allyl halides, one of the bands appears to show splitting due to spin-orbit coupling. The ionization potentials have been correlated in the related structural series.

Photoelectron spectroscopy of hydrogen-bonded systems: spectra of monomers, dimers and mixed complexes of carboxylic acids

By cooling the target chamber of a photoelectron spectrometer, the photoelectron spectra of dimers and mixed complexes of carboxylic acids have been obtained. By comparison of the spectra with each other and with those of the monomers, it has been possible to assign several bands to ionization from specific molecular orbitals. Hydrogen-bonding changes most ionization potentials of the monomers but not by more than about 0.5 eV. In particular, the ionization potential of an electron from a non-bonding orbital on the proton donor group is decreased and that from a non-bonding orbital on the electron donor group is increased. This is consistent with most theories of hydrogen bonding. In the mixed complexes it makes the first ionization potential higher than that of the free acids, dimers, however, are complicated by the initial degeneracy of their orbitals and this results in their first ionization potential being lower than for the free acid. There is also some evidence that the hydrogen bonds in a complex between different acids are of unequal strength.

X-ray spectroscopic studies of bonding in transition metal germanides

The electronic structure of transition metal germanides has been studied by X-ray spectroscopy. The germanides were the M 1.67Ge, MGe and MGe 2 compounds, where M was Ni, Co, Fe, Mn. The changes in distribution of the 3 d-4 s-4 p bonding electrons for both the metal and germanium were investigated by measurement of the K β 5 X-ray spectrum intensity and shape. The intensities of the K β 5 spectra of Fe, Co, and Ni increased in the germanides. This indicates increased overlap of the metal 3 d-4 p electrons. The intensities of the germanium K β 5 and the manganese K β 5 spectra decreased in the germanides. The K β 5 intensities have been correlated with regard to specific molecular orbitals involving the symmetry of the covalent metal-germanium bonds in the compounds.