When analyzed in the dry, powdered form, most of the hundreds of modern synthetic organic pig-ments that have been introduced throughout the 20th century can be effectively characterized by direct temperature-resolved mass spectrometry (DTMS) [S.Q. Lomax, M. Schilling, T. Learner, in: T. Learner, P. Smithen, J.W. Krueger, M. Schilling (Eds.), Modern Paints Uncovered, Getty Conservation Institute, Tate Modern, London, 2007, p. 105]. However, their detection in paint formulations is often far more difficult, as these pigments are usually present in only very low concentrations, due to their relatively high tint-ing strengths. The situation is also more complex when one attempts to identify these pigments from microscopic samples of paint taken from actual works of art, due to the frequent manipulation, mixing, or adulteration of paints by artists during their application. A project aiming to characterize the wide range of pigments found in the paints of Sam Francis (American, 1923-1994) prompted work to investi-gate more fully the sensitivity of a DTMS system by comparing various ionization conditions, including electron impact (EI) at 70 and 16 eV, and chemical ionization (CI) with iso-butane in both positive- and negative-ion modes. Overall, it was found that negative-ion CI conditions showed the best results for detecting the majority of synthetic organic pigments tested: the very limited fragmentation it produced in most of the pigments resulted in a much stronger and more readily detectable molecular ion that could be more easily distinguished from the lower m/z-value ions typically coming from other components in the paints.
Bouchard M, Rivenc R, Menke CA, Learner T. Micro-FTIR and Micro-RAMAN Study of Paints Used by Sam Francis. e-Preservation Science. 2009;6:27-37.
Raman microscopy and Fourier-transform infrared (FTIR) analyses were both utilized in a recent study of the paint-ing materials used by the American artist Sam Francis (1923-94), in particular a collection of sixty-four pots of custom-made, pre-mixed paints that were found in his Santa Monica studio after his death. Although other analyt-ical techniques were also used in this study, this paper reports on the performance of FTIR and Raman microscopy, with a particular emphasis on their relative ability to detect synthetic organic pigments. These pigments are often hard to detect in paint samples due to their very small particle size, and the fact that only minimal quantities are needed in some paint formulation to produce extremely vivid colours. In general, Raman microscopy was found to be more successful in detecting all pigments, both organic and inorganic. Sixteen different organic pigments were identi-fied by Raman microscopy in thirty-five of the paint sam-ples, including those from the azo, phthalocyanine, quinacridone, disazo, diarylide, dioxazine, indanthrone and perinone families. In contrast, FTIR only detected organic pigments successfully in eighteen of the paint samples, and in most of the cases where FTIR failed it was due to the strong and broad absorptions of the fillers. The inorganic pigments identified by Raman included natural and synthet-ic pigments such as hematite, goethite, magnetite, cobalt phosphate, cobalt titanate, ultramarine, amorphous materi-al such as graphite but also baryte and calcite fillers. FTIR was also effective in detecting fillers, but very few of the inorganic pigments. However, FTIR appeared much better suited to the detection of the binder, primarily an acrylic emulsion, which typically gave very strong and distinctive peaks, compared to the fairly weak and broad peaks visible with Raman microscopy. The two techniques appeared very complementary and the use of both was required to gather a complete understanding of Francis’ paints composition.


Steinbach C, ik MF\ arn\ \, Buck U, Brindle CA, Janda KC. Electron impact fragmentation of size-selected krypton clusters. The Journal of Physical Chemistry A. 2006;110(29):9108-9115.
Clusters of krypton are generated in a supersonic expansion and size selected by deflection from a helium target beam. By measuring angular distributions for different fragment masses and time-of-flight distributions for fixed deflection angles and fragment masses, the complete fragmentation patterns for electron impact ionization at 70 eV are obtained from the dimer to the heptamer. For each of the neutral Krn clusters studied, the main fragment is the monomer Kr ion with a probability fn1 90%. The probability of observing dimer + > Kr2 ions is much smaller than expected for each initial cluster size. The trimer ion Kr3 appears first from + + the neutral Kr5, and its fraction increases with increasing neutral cluster size n, but is always much smaller than that of the monomer or dimer. For neutral Kr7, all possible ion fragments are observed, but the monomer still represents 90% of the overall probability and fragments with n 3 contribute less than 1% of the total. > Aspects of the Krn cluster ionization process and the experimental measurements are discussed to provide possible reasons for the surprisingly high probability of observing fragmentation to the Kr monomer ion. +


Brindle CA, Chaban GM, Gerber B, Janda KC. Anharmonic vibrational spectroscopy calculations for (NH3)(HF) and (NH3)(DF): fundamental, overtone, and combination transitions. Physical Chemistry Chemical Physics. 2005;7(5):945-954.
In order to study the effects of hydrogen bonding on the spectroscopic properties of (NH3)(HF) and (NH3)(DF) complexes, vibrational spectra (including fundamental, overtone and combination transitions) were calculated using the vibrational self consistent field (VSCF) method. This ab initio VSCF method accounts for both one-dimensional anharmonicity and pair-wise mode-mode couplings for all vibrational modes of the molecule, using points on the potential energy surface (at the MP2/TZP level of theory in this study). An analysis of the coupling strength shows surprisingly important coupling effects from pair-wise interactions not expected to be major. This indicates the benefits of including all pair-wise mode-mode couplings for weakly bound systems. Hydrogen bonding induces  20% red shifts for the HF and DF stretch frequencies. The corrections due to anharmonicity for these modes are -6% and -5%, respectively. The anharmonic corrections for the intermolecular stretch of (NH3)(HF) and (NH3)(DF) are each about -5%. The NH3 umbrella motion has virtually no anharmonic correction in the complex, whereas free ammonia experiences a -15% correction. Also, the closing motion as well as the opening motion is restricted. The 1 + 1 combination transition of the proton stretching and intermolecular stretching modes has remarkably large intensity, larger even than the intensities for the first overtone of the proton stretching modes. The anharmonic frequency for the fundamental HF stretch, 3268 cm?1, is in good agreement with the experimental gas phase result, 3215 cm-1. A comparison to solid rare-gas matrix data shows that the VSCF frequencies are a consistent improvement over the harmonic approximation. The experimental data also support the use of the MP2 level of theory for the associated electronic structure calculations.