Complex refractive index of Titan's aerosol analogues in the 200-900 nm domain

The main gas-phase constituents of Titan's upper atmosphere, N-2 and CH4, are photolyzed and radiolyzed by solar photons and magnetospheric electrons, respectively. The primary products of these chemical interactions evolve to heavier organic compounds that are likely to associate into the particles of haze layers that hide Titan's surface. The different theories and models that have been put forward to explain the characteristics and properties of the haze composites require a knowledge of their optical properties, which are determined by the complex refractive index. We present a new set of values for refractive index n and extinction coefficient k calculated directly from the transmittance and reflectance curves exhibited by a laboratory analogue of Titan's aerosols in the 200900 nm range. Improvements in the aerosol analogue quality have been made. The effects of variables such as the uncertainty in sample thickness, aerosol porosity, and amount of scattered light on the final n and k values are assessed and discussed. Within the studied wavelength domain, n varies from 1.53 to 1.68 and k varies from 2.62 x 10(-4) to 2.87 x 10(-2). These final n and k values should be considered as a new reference to modelers who compute the properties of Titan's aerosols in trying to explain the atmospheric dynamics and surface characteristics. (C) 2002 Elsevier Science (USA).