We have measured the electron drift velocity, longitudinal diffusion, and the effective ionization coefficients in the gaseous mixture of CF3I–SF6 over the density-normalized electric field intensity E/N, from 375 to 500 Td (1 Td = 10−17 V cm2). A pulsed Townsend technique was used. Overall, the gas mixture compositions were varied from 50 to 90% CF3I. We have found that the limiting field strength E/N lim of the CF3I–SF6 mixture is superior to that of CF3I–N2, and always higher than that of SF6. Moreover, over the whole mixture range, the range of the limiting field strength for the CF3I–SF6 mixture is 360–437 Td, these limits corresponding for pure SF6 and CF3I, respectively.

In pre‐Hispanic Mesoamerica, pigments and dyes were used in the elaboration of a large variety of colored objects. Obtaining information regarding the objects' material composition is useful in restoration and preservation processes, as well as for recovering knowledge of its production technology and the context and history of the object. Yellow colors have been obtained from a large variety of Mexican natural resources. Although mineral yellow pigments, such as orpiment and oxides, are relatively easy to identify by nondestructive and noninvasive techniques (X‐ray fluorescence, Raman spectroscopy, fiber optics reflectance spectroscopy, and Fourier transform infrared spectroscopy), organic yellow colorants are difficult to analyze by these techniques. Therefore, most works dealing with the identification of yellow dyes use destructive methods such as liquid chromatography–mass spectrometry. The aim of this work is to elaborate a methodology based on Raman spectroscopy and surface‐enhanced Raman spectroscopy for the study of yellow colorants used in pre‐Hispanic and colonial Mexico, in order to aid in their identification by spectroscopic techniques. The yellow colorants selected for this work were extracted from local plants: zacatlaxcalli (Cuscuta tinctoria), old fustic (Maclura tinctoria), weld (Reseda luteola), marigold (Tagetes erecta), and xochipalli (Cosmos sulphureus).

No abstract

No abstract

One contribution of 14 to a theme issue 'Raman spectroscopy in art and archaeology'.