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Aims.The goal is to develop a database of rate coefficients for rotational state-to-state transitions in H2O + H2O collisions that is suitable for the modeling of energy transfer in nonequilibrium conditions, in which the distribution of rotational states of H2O deviates from local thermodynamic equilibrium. Methods.A two-temperature model was employed that assumed that although there is no equilibrium between all possible degrees of freedom in the system, the translational and rotational degrees of freedom can be expected to achieve their own equilibria independently, and that they can be approximately characterized by Boltzmann distributions at two different temperatures,TkinandTrot. Results.Upon introducing our new parameterization of the collisional rates, taking into account their dependence on bothTkinandTrot, we find a change of up to 20% in the H2O rotational level populations for both ortho and para-H2O for the part of the cometary coma where the nonequilibrium regime occurs.
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Non-equilibrium dynamics at the gas–liquid interface: State-resolved studies of NO evaporation from a benzyl alcohol liquid microjet
First measurements of internal quantum-state distributions for nitric oxide (NO) evaporating from liquid benzyl alcohol are presented over a broad range of temperatures, performed by liquid-microjet techniques in an essentially collision-free regime, with rotational/spin–orbit populations in the 2 Π 1/2,3/2 manifolds measured by laser-induced fluorescence. The observed rotational distributions exhibit highly linear (i.e., thermal) Boltzmann plots but notably reflect rotational temperatures ( T rot ) as much as 30 K lower than the liquid temperature ( T jet ). A comparable lack of equilibrium behavior is also noted in the electronic degrees of freedom but with populations corresponding to spin–orbit temperatures ( T SO ) consistently higher than T rot by ∼15 K. These results unambiguously demonstrate evaporation into a non-equilibrium distribution, which, by detailed-balance considerations, predict quantum-state-dependent sticking coefficients for incident collisions of NO at the gas–liquid interface. Comparison and parallels with previous experimental studies of NO thermal desorption and molecular-beam scattering in other systems are discussed, which suggests the emergence of a self-consistent picture for the non-equilibrium dynamics.
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- PAR ID:
- 10412964
- Date Published:
- Journal Name:
- The Journal of Chemical Physics
- Volume:
- 158
- Issue:
- 14
- ISSN:
- 0021-9606
- Page Range / eLocation ID:
- 144703
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1063/5.0143254
