J.D.W. van Voorst

Electron Spin Resonance of Fe(CN)5NO3− and Fe(CN)5NOH2−

It has been shown by means of ESR in aqueous, nonaqueous, and aprotic solution as well as in irradiated single crystals in the temperature range of 77°—300°K, that two paramagnetic species are obtained by reduction of pentacyanonitrosoferrate(II) which are in a protonation—deprotonation equilibrium. In support of the ESR data, electronic spectra have been investigated and pKa values have been determined by acidimetry and spectrophotometry. The spin density was calculated from ESR data of nFe(CN)5NO3− for n=56, 57 isotopes and found to be consistent with the lowest antibonding orbital being mainly π*NO.

C-nitroso compounds—II : On the photochemical and thermal formation of nitroxides from nitroso compounds, as studied by E.S.R.

Abstract It is demonstrated that nitroxides can be generated by photochemical or thermal decomposition of C-nitroso compounds. The nitroxide-formation takes place in both cases via the nitroso monomer. The influence of the wavelength on the photochemical reaction is discussed.

Bonding in Sandwich Compounds

A study is made of the bonding in sandwich compounds by means of ESR and susceptibility measurements. Data obtained for vanadocene and nickelocene are discussed in terms of various calculated MO schemes. The experimental results are compatible with the level order e2g ≲ a1g < e1g* for the highest‐bonding and lowest‐antibonding orbitals, all orbitals having a strong metal 3d character. The assignments given for the ground‐state configurations are quantitatively checked by comparison of calculated and experimental D and g values. Both spin–orbit and spin–spin coupling are shown to give a substantial contribution to the value of D. The excitation energies used in the perturbation calculation of the DLS and g values are obtained from a ligand‐field treatment of the low‐energy bands in the optical absorption spectra.

Zero-field splitting in the triplet ground state of nickelocene

Abstract The magnetic susceptibility of nickelocene was measured from 6.5° - 300°K. The measured curve can be fitted with the parameters: g‖ = 2.0

Singlet excited monomer and excimer absorptions of pyrene

Abstract The absorption and polarization spectra from the first excited singlet state of pyrene and the absorption spectrum of the pyrene excimer are presented. These results were obtained by laser flash spectroscopy using a frequency doubled ruby laser pulse of 6 nanoseconds halfwidth. A qualitative preliminary assignment of the bands is given.

SCF Cl calculations and assignment of the S1 → Sn absorption spectra of 1,1′-binaphthyl in different molecular conformations

Abstract An SCF calculation followed by extensive configuration interaction between all singly-excited singlet states has been performed for 1,1′-binaphthyl as a function of the dihedral angle. With these results an assignment of the electronic absorption bands in rigid and in fluid solution is given.

Intermediate strong coupling and vibrational redistribution effects in the S2 emission of pyrene

Abstract Upon excitation of pyrene in the third excited singlet state normal (τ = 75 nsec) and hot band (τ = 15 nsec) fluorescence of the second excited singlet has been observed. Both emissions exhibit intermediate strong coupling characteristics while the lifetime of the latter is also affected by a vibrational redistribution process.

Triplet excimer emission from pyrene single crystals

Abstract Two new, but distinct delayed emissions are found from pyrene single crystals in the temperature region 77°–300°K, which are attributed to the emission of two types of triplet excimer.

Sequence congestion and temperature effects on the fluorescence of isolated pyrene molecules

Abstract The temperature dependences of (i) the relative yield of the S2 fluorescence and (ii) the fluorescence decay times measured in the S1 and S2 emission regions of pyrene vapour have been measured at very low pressures. The results demonstrate that the thermal equilibrium distribution of vibrational energy in the electronic ground state of the molecule is transferred to the excited electronic state by the excitation process. This phenomenon is ascribed to sequence congestion effects.

Flash photolysis of negative aromatic ions in liquid solutions

Abstract Photo-oxidation of fluid solutions of negative aromatic ions at low temperatures results in the production of solvated electrons. Photolysis of the associated ion pairs of the negative aromatic ions and their alkali counterions at higher temperatures gives rise to the formation of a species composed of an alkali metal ion and a solvated electron, presumably to be considered as an ion pair. It has a characteristic single absorption band located at 12000 cm−1 for Na+, e− and at 9000 cm−1 for K+, e−.