Cross-section measurements of multilayer automotive paint samples using combined Raman spectroscopy and LIBS.

Multilayer automotive paint samples can be important evidence in forensic investigations but due to their inherent complexity it is a challenging task to analyze them. We herein present a method for a comprehensive chemical sample characterization based on the subsequent measurements of paint samples with Raman spectroscopy and laser induced breakdown spectroscopy (LIBS) at the same sampling points along the cross-sections of the paints. The method requires minimal sample preparation because the layers do not have to be separated. In combination with multivariate data analysis (namely k-means) the proposed method provides information both on the distribution of molecular compounds as well as elements which could then be used for the discrimination of different paints. Eight different samples were investigated and individual chemical profiles were found whereby a spatial resolution of close to 10 µm could be demonstrated. Investigation of different samples of the same origin showed similar profiles revealing the reproducibility of the proposed method. We therefore believe that our approach could be a good addition to the methods used so far for the analysis of paint samples.

pH-Dependent Flavin Adenine Dinucleotide and Nicotinamide Adenine Dinucleotide Ultraviolet Resonance Raman (UVRR) Spectra at Intracellular Concentration.

The ultraviolet resonance Raman spectra of the adenine-containing enzymatic redox cofactors nicotinamide adenine dinucleotide and flavin adenine dinucleotide in aqueous solution of physiological concentration are compared with the aim of distinguishing between them and their building block adenine in potential co-occurrence in biological materials. At an excitation wavelength of 266 nm, the spectra are dominated by the strong resonant contribution from adenine; nevertheless, bands assigned to vibrational modes of the nicotinamide and the flavin unit are found to appear at similar signal strength. Comparison of spectra measured at pH 7 with data obtained pH 10 and pH 3 shows characteristic changes when pH is increased or lowered, mainly due to deprotonation of the flavin and nicotinamide moieties, and protonation of the adenine, respectively.

Mode-selective O-H stretching relaxation in a hydrogen bond studied by ultrafast vibrational spectroscopy.

The ultrafast relaxation of the excited O-H stretching vibration is studied by ultrafast infrared-pump/infrared-probe and infrared-pump/Raman-probe spectroscopy. We demonstrate a 200 fs lifetime of the hydrogen-bonded O-H stretching mode in 2-(2'-hydroxy-5'-methyl-phenyl)benzotriazole (TINUVIN P). O-H stretching relaxation occurs through a few major channels that all involve combination and overtone bands of modes with considerable in-plane O-H bending character. In particular, the mode, which contains the largest O-H bending contribution, plays a prominent role for primary processes of intramolecular vibrational energy redistribution. Theoretical calculations of vibrational energy transfer rates based on a Fermi golden rule approach account for the experimental findings.