Non-equilibrium thermodynamics of the gasliquid interface: Measurement of the Onsager heat of transport for nitrous oxide at the surface of water

The Onsager heat of transport, Q*, for nitrous oxide at the surface of water has been measured by using high-resolution diode-laser spectroscopy to monitor the partial pressure of N₂O as a function of the temperature difference across a 5-mm vapour gap above the water surface. The metal surface above the vapour gap was conditioned with ammonia prior to the measurements, to enable efficient thermal accommodation at that surface, which allowed the temperature difference to be as large as 15 K. We find Q* 6.6 ± 0.85 kJ mol¹, so that Q*/RT is 2.9 at T 275.15 K. These experiments are a necessary preliminary to a planned series of measurements of Q* for CO₂ at the surface of simulated sea water.