Optical Constants of Sulfuric Acid; Application to the Clouds of Venus?

TLDR

The study aimed to determine the real and imaginary parts of the complex refractive index of sulfuric acid solutions by measuring spectral transmission and reflection in the visible and near‑infrared. Using Kramers‑Kronig phase‑shift analysis of reflection data collected at 300 K for solutions ranging from 95.6 % to 25 % by weight, the authors derived the refractive indices across 400–4000 cm⁻¹. The resulting optical constants—n over the full range and k in the near‑infrared with visible upper limits—enable interpretation of Venus cloud polarization and suggest that cloud droplets at 250 K contain more than 70 % sulfuric acid. Various possibilities are discussed.

Abstract

With the purpose of obtaining the real and imaginary parts of the complex refractive index N; = n + ik, we have made quantitative measurements of spectral transmission and reflection of sulfuric acid solutions in the visible and near infrared. On the basis of the results, we have obtained values for n throughout the entire region and values of k in the near infrared together with upper limits for k in the visible region. These optical constants can be used to interpret the results of polarization studies of solar radiation that has been scattered by the clouds of Venus. We have Kramers-Kronig phase-shift analysis to obtain values of n and k from reflection measurements in the intermediate infrared region (400-4000 cm(-1)). Our measurements were made at 300 K on sulfuric acid solutions having concentrations by weight of 95.6, 84.5, 75, 50, 38, and 25%. If the particles in the Venus clouds consist of liquid droplets of sulfuric acid at a temperature of 250 K, comparison of existing Venus data with our data suggests that the acid concentration is probably higher than 70%. Various possibilities are discussed.