Forensic Scientist, Washington State Crime Laboratory, Washington State Patrol, Seattle, WA
(Received 6 June 1995; accepted 6 October 1995)
A survey of U.S. automobile original topcoats (1974–1989) for binder and pigment compositions has been conducted using infrared spectroscopy. Data were obtained from panels of the Reference Collection of Automotive Paints for single layer topcoats, excluding basecoat/clearcoat finishes. This paper describes the occurrence in these topcoats of acrylonitrile, a copolymer used in some acryiic melamine enamels, and iron ferrocyanide, an inorganic pigment used in some blue and green paints. Both of these components produce characteristic C≡N stretching fundamentals, which occur in a spectral region devoid of other significant absorptions. Because of this, they are usually easy to detect and assign, and since the spectra of most U.S. automobile original topcoats do not contain these peaks, their presence can serve as useful markers for identifying certain topcoats when used in conjunction with microscopic data. Of particular significance for hit-and-run cases, acrylonitrile absorptions occur predominantly for some topcoats used on certain Ford/Chrysler/Jeep/American Motor vehicles manufactured before 1985, with the majority of these used on Fords from the 1970s. Polyurethane isocyanate N=C=O stretching absorptions, which also occur in this same spectral region, were not detected for any of the topcoats of this study.
Paper ID: JFS13924J