Characterisation and classification of automotive clear coats with Raman spectroscopy and chemometrics for forensic purposes

Abstract

The clear coats from a collection of automotive paint samples of 139 vehicles, covering a range of Australian and international vehicle manufacturers and sold in Western Australia, were characterised using FT-Raman spectroscopy. Principal component analysis (PCA) revealed 19 distinct classes that were associated with the vehicles' manufacturer and model, and in the case of Australian manufacturers, the years of manufacture. Linear discriminant analysis based on the PCA groupings gave excellent discrimination between the groups with 96.9% of the calibration set and 97.6% of the validation set being correctly classified. Although the sample set comprised only vehicles available in Australia, the methodology used is universal and hence applicable in any jurisdiction that is willing and able to generate a statistically significant data set and maintain and update it as new vehicles appear on the market. A FT-Raman spectroscopy-based database would rapidly provide information regarding vehicle origin and manufacture and hence generate investigative leads for questioned paint samples found at incident sites.

Recent advances in linear and non‐linear Raman spectroscopy. Part XI

“…More specifically, the clear coats from a collection of automotive paint samples of 139 vehicles, covering a range of Australian and international vehicle manufacturers and sold in Western Australia, were characterised using FT‐Raman spectroscopy. Although the sample set comprised only vehicles available in Australia, the methodology used is universal and hence applicable in any jurisdiction that is willing and able to generate a statistically significant data set and maintain and update it as new vehicles appear on the market …”

“…Although the sample set comprised only vehicles available in Australia, the methodology used is universal and hence applicable in any jurisdiction that is willing and able to generate a statistically significant data set and maintain and update it as new vehicles appear on the market. [194] 20 | VIBRATIONAL STUDIES IN CHEMISTRY Accurate vibrational analysis of medium sized molecules can be easily achieved these days to a high degree of reliability and accuracy resulting from the combination of IR absorption and Raman scattering measurements with quantum chemistry calculations typically using density functional theory (DFT). In keeping with recent JRS policy, papers reporting routine vibrational quantum analyses without a novel Raman aspect are referred to other journals for consideration.…”

Appearance and Spectroscopic Characterization of Automotive Coatings for Forensic Purposes

“…binder. 59 The peak at roughly 978 cm -1 is ascribed to melamine triazine ring breathing. The clear coat spectrum of sample 3 (middle) exhibited the characteristic acrylic peaks in the 1300 cm -1 to 1800 cm -1 region, and styrene peaks at lower frequencies.…”

“…This was expected as near-IR lasers have been shown to induce less fluorescence in the literature. 43,59 The pigments identified in the base coat spectra are noted with their CI name. to the absolute frequency measurement in IR spectroscopy.…”

“…The 1595 cm -1 peak is due to some aromatic derivative, likely the quadrant stretch of some benzene derivative used in the clear coat. 59 Styrene was ruled out as it exhibits a strong, characteristic peak at 1000 cm -1 , which man-ifests at a positive factor loading in PC 1. The 1732 cm -1 peak is the characteristic carbonyl stretch, attributed to the acrylic binder of most of the clear coats examined.…”