The determination of the complex refractive indices of some concentrated aqueous salt solutions at submillimetre wavelengths

Recent developments in far infrared laser spectrometry and dispersive Fourier transform spectrometry have allowed the full spectral variation of both parts of the complex refractive indices of some aqueous salt solutions in the spectral region 25–450 cm^?1 to be determined. The salts studied were LiCl, LiClO₄, NaCl, NaClO₄, NaI, KCl, KBr, KI, KF, MgCl₂, Mg(ClO₄) and Bu₄NBr (tetrabutylammonium bromide). The results show that in the presence of some electrolytes the optical constants of the solution differ significantly from those of pure water, and that in localised spectral regions the absorption can be many times less than that of pure water.     

The origin of fluorescence from trans-trans diphenylbutadiene

Fluorescence decay time and yield of trans-trans diphenylbutadiene in methylcyclohexane/isohexane and propylene glycol were measured between ?50 and +50°C. The radiative rate parameter is independent of solvent and temperature, with a mean value of 8.2 × 10⁸ s^?1. This is similar to trans-stilbene but unlike longer polyenes, and is consistent with emission from ¹B^*_u rather than the low-lying ¹Ag^*_g state.     

Stable isotope analysis of white-tailed deer teeth as a paleoenvironmental proxy at the Maya site of La Joyanca,northwestern Petén,Guatemala*

ABSTRACT

Carbon and oxygen isotopes ratios from herbivore teeth have previously been used as paleo-environmental proxies in temperate zones. However, their utility in tropical zones remains uncertain. In this study, sequential sub-samples from white-tailed deer (Odocoileus virginianus) teeth (second and third molars) from the Maya archaeological site of La Joyanca, located in northwestern Petén, Guatemala, show that δ¹⁸O of enamel carbonate corresponds broadly to modern observed precipitation δ¹⁸O over the 10-month period of tooth formation, capturing rainfall seasonality. The analyses also detect significant diachronic differences in the δ¹⁸O between the periods 1100–1000 BP (850–950 A.D.) and 1000–900 BP (950–1050 A.D.) at La Joyanca. The δ¹³C in both periods are indicative of a C₃-plant based diet, which suggests cultivation of maize did not differentially affect deer diet during this period.     

Effect of available volumes on radial distribution functions

The traditional method of analyzing solution structuring properties of solutes using atom–atom radial distribution functions (rdfs) can give rise to misleading interpretations when the volume occupied by the solute is ignored. It is shown by using the examples of O(4) in α- and β-D-allose that a more reliable interpretation of rdfs can be obtained by normalising the rdf using the available volume, rather than the traditional volume of a spherical shell. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 363–367, 1998     

The photophysics of trans-stilbene

The fluorescence lifetime of trans-stilbene in dilute methylcyclohexane/iso-hexane solution has been measured and the mean S₁ radiative (k_F), radiationless (k_I) and cis-isomerization (k_C) rate parameters have been determined from ?90 to 60°C. S_i consists of a fluorescent trans (¹B_u^*) state (k_F⁰ = 6.0 × 10⁸ s^?1) which undergoes reversible thermal-activated rotational internal conversion (ΔH = 1.75 kcal mole^?1, ΔS = 10.6 cal deg^?1 mole^?1) to a non-fluorescent perp (¹A_g^*) state. p(¹A_g^*) lies 610 cm^?1 above t (¹B_u^*) with an intermediate S₁ potential maximum. p(¹A_g^*) undergoes internal conversion(k_I.^∞ = 5.8 × 10⁸ s^?1) to p (¹A_g) leading to cis-isomerization. This is the main isomerization channel over the whole temperature range.