Robert Withnall

Indigo, woad, and Tyrian Purple : Important vat dyes from antiquity to the present

Abstract This article reviews the origin, use and history of indigo, woad and Tyrian Purple, which are among the most ancient of dyes. The emphasis is on the chemistry of the production and syntheses of the dyes, together with some reference to the use of their spectroscopic properties as an aid to their identification in artefacts.

Synthesis, structural characterisation and Raman spectroscopy of the inorganic pigments lead tin yellow types I and II and lead antimonate yellow: their identification on medieval paintings and manuscripts

Lead tin yellow type I (Pb2SnO4) and type II (PbSn1–xSixO3) have each been prepared in a high-temperature furnace, and the preparative conditions defined. The crystal structure of type II has been refined from powder X-ray diffraction data and indicates that the Sn and Si atoms are randomly distributed over the same type of site with Sn/Si ratio ≈ 3/1 (i.e., x≈¼). The Raman spectra of each form and also that of lead antimonate yellow (Pb2Sb2O7) have been obtained. Raman microscopy is shown to be an effective technique whereby these inorganic yellow pigments as minute (≈ 1 µm) grains may be identified on medieval manuscripts and paintings.

Applications of fourier transform IR spectroscopy to the determination of photo-oxidation quantum yields for halocarbons

Abstract Fourier transform IR spectroscopy has been applied to the quantitative analysis of the products from the photo-oxidation of CF 2 Cl 2 and CF 3 Br by molecular oxygen. Φ 184.9 COF 2 for CF 2 Cl 2 -O 2 mixtures was measured as 1.08 ± 0.08 in good agreement with previous studies. Φ 184.9 COF 2 for CF 3 BrO 2 mixtures has been measured for the first time in this work, its value being 1.02 ± 0.08.

A fourier-transform infrared investigation of the gas-phase photolysis of nitrous oxide at 184.9 nm

The nitrous oxide actinometer at 184.9 nm has been investigated using Fourier-transform infrared spectroscopy as both a quantitative technique to determine Φ184.9NO and as a qualitative analytical method to observe secondary photoproducts in the system. The quantum-yield value of 1.0 ± 0.2 for Φ184.9NO obtained in this work must be regarded as a lower limit, because unquantifiable amounts of NO2 and BrNO were formed in the photolysis cell over the data collection period. In view of these results, the reported value for Φ184.9NO of 1.2 using chemiluminescence methods is recommended in preference to values of ca. 0.82 obtained by mass spectrometry.

Resonance-Raman spectra and excited-state geometry of the bis(µ-acetato)(µ-oxo) ruthenium(III) dimeric ion [Ru2(µ-O2CMe)2(µ-O)(py)6]2+(py = pyridine)

The Raman spectra of [Ru2(µ-O2CMe)2(µ-O)(py)6][PF6]2(py = pyridine) at resonance with the π–π* transition at 588 nm of the Ru–O–Ru bridge display a progression in ν1, νsym(RuORu), 597 cm–1, reaching 5ν1 and five subsidiary progressions in ν1. The spectra and associated excitation profiles have been used in conjunction with a transform method to establish that the Ru–O bond length increases by ≈ 1.2 pm on excitation to this excited state.