Studies of water evaporation with raman thermometry Franky Bernal 1,2 , Tony Rizzuto 3 and Richard Saykally 1,2 1 Department of Chemistry, University of California, USA, 2 Chemical Sciences Division, Lawrence Berkeley National Lab, USA, 3 Department of Chemistry, Elon University, USA A complete mechanistic description of water evaporation and condensation, inverse processes that govern a myriad of atmospheric phenomena, remains incomplete in modern science. Several groups have studied neat water in efforts to extract an evaporation coefficient, a parameter crucial in describing the kinetics of evaporation. Over the last few decades, the evaporation coefficient (γ) has been reported over the range 0.001 – 1. 1 The large dispersion in these measurements highlights the challenges associated with an accurate measurement of this quantity and the theory used to describe it. Our group has developed an experimental technique employing Raman Thermometry on liquid microjets in vacuum to determine the temperature of spherical microdroplets as they evaporate in a condensation-free environment. We previously reported γ for H 2 O and D 2 O as 0.62 +/- 0.09 2,3 , and found minimal change with added solutes such as ammonium sulfate and acetic acid. 4,5 However, Rizzuto et al recently found HCl solution concentration to have a significant impact on γ 6 . We are expanding these studies to other strong acids such as HBr and H 2 SO 4 , quantifying their effects on γ. Using a simple evaporation model based on the Hertz-Knudsen equation, we compare the extracted γ values of these acidic solutions to that of neat water. References 1. Marek, R.; Straub, J. Analysis of the Evaporation Coefficient and the Condensation Coefficient of Water. J. Heat Mass Transf. 2001 , 44 (1), 39–53. 2. Smith, J. D.; Cappa, C. D.; Drisdell, W. S.; Cohen, R. C.; Saykally, R. J. Raman Thermometry Measurements of Free Evaporation from Liquid Water Droplets. Am.Chem. Soc . 2006 , 128 , 12892−12898. 3. Drisdell, W. S.; Cappa, C. D.; Smith, J. D.; Saykally, R. J.; Cohen, R. C. Determination of the Evaporation Coefficient of D2O. Chem. Phys. Discuss . 2008 , 8, 8565−8583. 4. Duffey, K. C.; Shih, O.; Wong, N. L.; Drisdell, W. S.; Saykally, R. J.; Cohen, R. C. Evaporation Kinetics of Aqueous Acetic Acid Droplets: Effects of Soluble Organic Aerosol Components on the Mechanism of Water Evaporation. Chem. Chem. Phys . 2013 , 15 , 11634−11639. 5. Drisdell, W. S.; Saykally, R. J.; Cohen, R. C. On the Evaporation of Ammonium Sulfate Solution. Natl. Acad. Sci. U. S. A. 2009 , 106, 18897−18901. 6. Rizzuto, A. M.; Cheng, E. S.; Lam, R. K.; Saykally, R. J. Surprising Effects of Hydrochloric Acid on the Water Evaporation Coefficient Observed by Raman Thermometry. Phys. Chem. C 2017 , 121 (8), 4420–4425.
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