Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 

Abstract: We have characterized the protolytic equilibria of fluorescein and determined the spectroscopic properties of its protolytic forms. The protolytic constants relating the chemical activities (which at low ionic strength equal concentrations) of the cation, neutral form, anion and dianion are pK1 = 2.08, pK2 = 4.31, and pK3 = 6.43. All forms have rather high molar absorptivities being e437FH31 = 53 000, e434FH2 = 11 000, e453FH− = 29 000 (e472FH = 29 000) and e490F2 = 76 900 M−1 cm−1 for the cation, neutral form, anion and dianion, respectively. The dianion has the most intense fluorescence with a quantum yield of 0.93 but also the anion shows considerable fluorescence with a quantum yield of 0.37. The neutral and cationic species are upon excitation converted into the anion and fluoresce with quantum yields of about 0.30 and 0.18, respectively.

Abstract: Sixty pigments, minerals and media have been analysed by Fourier-transform Raman (FT-Raman) microscopy in order to assemble a database of reference FT-Raman spectra for scientists working at the Arts–Science interface. An earlier library of Raman spectra compiled using visible excitation has been extended by the addition of 22 further reference spectra obtained with 780.0, 647.1, 632.8 and/or 514.5 nm excitation. The relative merits of 1064 nm and visible excitation are discussed.

Abstract: The IR (3200–30 cm−1) spectra have been recorded for S-methyl-N,N-dimefhylthiocarbamate, (CH3)2NC(O)SCH3, and its isotopomers, S-d3, N-d6 and N-d9, for the gas and liquid. Additionally, the Raman spectra (3200–10 cm−1) for the solid and liquid, with qualitative depolarization ratios, have been obtained for all the isotopes. These data are interpreted on the basis that the s-cis conformer (the S-methyl group oriented eis to the carbonyl group) with Cs symmetry is the only form existing in all three phases for this molecule. A complete vibrational assignment proposed for the -d0 molecule is facilitated by the availability of spectral data for five different isotopomers. A normal coordinate analysis has been carried out utilizing ab initio calculations with the 3–21G* basis set. The potential energy distributions and ab initio calculated frequencies have allowed a clarification of some of the corresponding results obtained from experiment. Structural optimizations and potential surface scan have also been carried out by ab initio calculations with the 3–21G* basis set. These results are compared with some previous studies on this molecule as well as on similar molecules.

Abstract: To assist in the greatly increasing number of applications of Raman microscopy as a tool for non-intrusive, in situ archaeometric analysis, the Raman spectra of over 60 pigments, both natural and synthetic, known to have been in use before ≈ 1850 AD, have been studied by Raman microscopy. Fifty-six pigments have yielded high quality spectra which have been arranged, by colour, into a spectroscopic library for reference purposes. The spectroscopic files may be downloaded from http://www.ucl.ac.uk/chem/resources/raman/speclib.html