James Ferguson

The Effects of Exchange Interactions in the Spectra of Octahedral Manganese. II. Compounds

Earlier experimental work (J. Ferguson, H.J. Guggenheim and Y. Tanabe, J. appl. Phys. 36 (1965) 1046, Phys. Rev. Letters 14 (1965) 737) on the Mn pair spectrum of KZnF 3 :Mn and the spectrum of KMnF 3 has been extended. The narrow bands of KMnF 3 and RbMnF 3 have been assigned and their abnormally high intensities established. The transition is an electric dipole one and oscillator strength (∼9.5×10 -7 for the 4000 A absorption) is temperature independent, corresponding to an allowed transition. The experimentally observed features of the pair absorption suggest a possible form of interaction between radiation and paramagnetic ion pair. The origin of this interaction is discussed and an order of magnitude argument is given to support the proposed mechanism. Related problems such as exchange interaction in excited states and the spectra of the concentrated materials are also considered.

A spectroscopic study of the photodimerization of anthracene sandwich dimers in dianthracene

The photodimerization of anthracene sandwich pairs embedded in dianthracene single crystals has been studied by absorption and fluorescence spectroscopy over a wide range of temperature (6–295 K). An excimer state has been found to be the intermediate state in the formation of the dianthracene. The fluorescence efficiency of the sandwich pair is unity at very low temperature while the quantum yield for the dimerization process is unity at high temperatures. The thermal activation energy for the photodimerization process has been determined directly as well as from temperature dependence measurements of the fluorescence intensity. The two methods yield 590 ± 25 cm-1 and 611 ± 20 cm-1 respectively for this energy. Corresponding measurements were also carried out with the perdeuterated anthracene sandwich dimer. These show a marked deuterium effect.

High resolution MCD spectroscopy of transition metal ions in fluoride crystals

A brief description of a high-resolution circular dichrograph is given. For MCD measurements a 0·52 T permanent magnet and silica flow tubes are used to obtain data with variable sample temperatures as low as 4·2 K. The MCD results provide an unambiguous assignment of the 4 A 1g and 4 Eg a states of Mn2+ in KMgF3 and KZnF3. The 4 Eg a state lies 90–100 cm-1 below 4 A 1g . A theoretical analysis of the MCD results confirms the assignment of the 4 A 1g state, while an analysis of the spin-orbit splitting of the 4 Eg a state has been carried out using all 252 |αLSJMJ > functions of the d5 configuration. The observed positions of the three components of 4 Eg a are accurately accounted for by Dq values appropriate to KMgF3 and KZnF3 and a spin-orbit coupling constant of approximately 300 cm-1.

Absorption studies of acid-base equilibria of dye solutions

Abstract The spectral behaviour of neutral molecules of acridine orange, 3,6-diaminoacridine and rhodoamine B dissolved in ethanol has been studied. Contrary to previous conclusions, the neutral molecules do not dimerize in ethanol solutions. The spectral changes, thought to involve dimer—monomer

A model for the interpretation of the electronic spectra of the complex ions M(bpy)32+ (M = Fe, Ru, Os) in D3 and C2 sites

Abstract A theoretical model of the electronic structure of the metal-to-ligand charge-transfer states of the complex ions M(bpy)32+ (M = Fe, Ru, Os) is described. It is applied to new spectroscopic data obtained for these ions in two host crystals. In one host the site symmetry of the guest is close to D3, while in the other it is C2. The model has four parameters, the spin-orbit coupling constant of M2+, the trigonal field splitting of the metal-ion d orbitals, the trigonal field splitting of the ligand orbitals and an exchange integral between the metal-ion d electrons and the ligand π electrons. Analyses of the absorption spectra are consistent with the energy order e ′ a1 for the metal-ion d orbitals. The major source of the charge-transfer intensity comes from the transfer term. A detailed analysis of the luminescence from Ru(bpy)32+ in both crystal hosts shows that three E states are involved and the model accounts for all of the essential features of the luminescence.

Electronic spectroscopy of M(bpy)2+3 (M = Fe, Ru, Os), Cr(bpy)3+3 and related compounds

Abstract Absorption and luminescence spectroscopy of the title compounds have been studied in single crystals, PVA foils and alcohol solutions. Particular attention has been given to crystal sites with defined symmetry (D 3 and C 2 for Fe, Ru, Os). The effect of 4,4′ substitution in bpy has been studied for Fe, Ru, and OS complexes and significant intensity flow out of the ligand absorption bands into the metal to ligand charge transfer bands has been found for Ru and Os, consistent with back π-bonding. CD, CPL, MCD, MCPL and time resolved luminescence spectroscopy have been used to help make assignments. All of these data support a delocalized description of the luminescent states, except in fluid solutions where a viscosity dependent relaxation to a localized charge transfer state occurs. The first detailed investigation of the excited states of chromium (III) trisbipyridine in crystals is reported.

The origins of the colours of yellow, green and blue sapphires

The absorption spectra of natural yellow sapphires are shown to be due to single Fe3+ and Fe3+  O2−  Fe3+ pairs, with the latter dominant. Blue and green sapphires have spectra dominated by Fe3+  O2−  Ti4+ and Fe2+  O2−  Fe3+ pairs.

The assignment of the luminescent states of Ru(bpy)2+3. MCPL and time-resolved luminescence at 2.0 K

The luminescent states of Ru(bpy)2+3 are shown to be not in thermal equilibrium below ≈6 K. Time-resolved luminescence spectra and MCPL spectra show that the emission comes from E states. The assignments preclude the possibility of static localization of charge in the luminescent states.

Localization of electronic excitation energy in Ru(2,2′-bipyridine)2(2,2′-bipyridine-4,4′-dicarboxylic acid)2+ and related complexes

Abstract The absorption spectra of Ru(2,2′-bipyridine) 2 (2,2′-bipyridine-4,4′-dicarboxylic acid) 2+ (I) and its diethyl ester (II) are closely related and are both significantly different from the spectra of the mono-protonated (Ia) and deprotonated (Ib) complexes. Luminescence polarization measurements show that for I and II the luminescent states have the transferred electron in the bipy-4,4′(COOH) 2 and bipy-4,4′(COOEt) 2 ligands, respectively, rather than in the unsubstituted bipy ligands.

Conformation effects in the spectroscopy and photochemistry of 1,2-di(9-anthryl)ethane. A model for the anthracene “excimer”

Abstract Single crystals of the photocycloadduct of 1,2-di(9-anthryl)ethane have been prepared and used as host matrices for the spectroscopic study of the photocleaved sandwich dimer. Similar studies were also carried out in a variety of rigid glasses which were then allowed to soften under controlled conditions. The various spectroscopic and photochemical properties have been interpreted in terms of different conformations of the anthracene moieties.