Optical measurement of the evaporation of sulfuric acid droplets

Abstract

Single micron-size sulfuric acid droplets are levitated in vacuum in a quadrupole trap through which passes the beam from a He–Ne laser. Scattered light is monitored by a fixed detector as cavity resonances are excited in the evaporating droplet. Mie-Debye theory is used to determine particle size, which, with kinetic theory, yields vapor pressure. Over the temperature range studied, −10 to +30°C, the vapor pressure of pure sulfuric acid is lnp(Torr) = (20.70 ± 1.74) − (9360 ± 499)/T(K).