Quantum-state-resolved studies of aqueous evaporation dynamics: NO ejection from a liquid water microjet
Abstract
This work presents the first fully quantum-state-resolved measurements of a solute molecule evaporating from the gas–liquid interface in vacuum. Specifically, laser-induced fluorescence detection of NO(2Π1/2, 3/2, v = 0, J) evaporating from an ∼5 mM NO–water solution provides a detailed characterization of the rotational and spin–orbit distributions emerging from a ⌀4–5 μm liquid microjet into vacuum. The internal-quantum-state populations are found to be well described by Boltzmann distributions, but corresponding to temperatures substantially colder (up to 50 K for rotational and 30 K for spin–orbit) than the water surface. The results therefore raise the intriguing possibility of non-equilibrium dynamics in the evaporation of dissolved gases at the vacuum–liquid-water interface. In order to best interpret these data, we use a model for evaporative cooling of the liquid microjet and develop a model for collisional cooling of the nascent NO evaporant in the expanding water vapor. In particular, the collisional-cooling model illustrates that, despite the 1/r drop-off in density near the microjet greatly reducing the probability of collisions in the expanding water vapor, even small inelastic cross sections (≲ 20 Å2) could account for the experimentally observed temperature differences. The current results do not rule out the possibility of non-equilibrium evaporation dynamics, but certainly suggest that correct interpretation of liquid-microjet studies, even under conditions previously considered as “collision-free,” may require more careful consideration of residual collisional dynamics.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Jan 23, 2019
- Source ID
- 10.1063/1.5083050
Entities
People
- David J. Nesbitt
- Mikhail Ryazanov
Organizations
- Air Force Office of Scientific Research
- National Science Foundation
- University of Colorado