Benzene Vapor Pressures at Titan Temperatures: First Microbalance Results

Abstract

The vapor pressure of crystalline benzene (C6H6) has been measured for the first time with a quartz-crystal microbalance under ultrahigh vacuum conditions from about 135 to 160 K, temperatures relevant for Titan’s atmosphere. Good agreement is found with the most recent thermodynamic analysis of higher-temperature literature results, but there is less satisfactory agreement with recently published low-temperature data obtained with a different laboratory method. An enthalpy of sublimation of 49.7 ± 0.1 kJ mol−1 for benzene is reported, and a few brief comments are made concerning the connections between our new data and Titan’s atmosphere. Supporting our benzene results are new vapor-pressure measurements for crystalline H2O ice and crystalline cyclohexane (C6H12). The latter are the first of their type and enable the two sets of recently published vapor pressures for solid benzene to be brought into close agreement.