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   https://doi.org/10.1103/PhysRevA.85.033421  

   Zhang, Bin ; Yuan, Jianmin ; Zhao, Zengxiu ( March 2012 , Physical Review A)
2. Ambient ionization mass spectrometry: real-time, proximal sample processing and ionization

   https://doi.org/10.1039/c7ay00948h  

   Javanshad, R. ; Venter, A. R. ( January 2017 , Analytical Methods)

   The definition of ambient ionization is updated from “no sample preparation” to sample preparation proximal and in real time with the ionization and analysis step. We differentiate between ambient ionization methods and the direct and hyphenated techniques. Ambient ionization has been reviewed many times and we summarise some of the approaches that reviews have taken to categorize the many ambient ionization methods. Due to the large number of permutations, frequent redundancy and complexity of the 80+ techniques developed so far, none of the review classifications is successful in classifying all the ambient ionization methods based on the chosen scheme. Likewise our classification based on major sample preparation method also fails at finding a good category for every method, but it does highlight the central role that real-time, proximal sample preparation plays in ambient analysis. 

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3. Strong-field ionization of water. II. Electronic and nuclear dynamics en route to double ionization

   https://doi.org/10.1103/PhysRevA.104.023108  

   Cheng, Chuan ; Streeter, Zachary L. ; Howard, Andrew J. ; Spanner, Michael ; Lucchese, Robert R. ; McCurdy, C. William ; Weinacht, Thomas ; Bucksbaum, Philip H. ; Forbes, Ruaridh ( August 2021 , Physical Review A)
4. Characterizing Extreme Emission-line Galaxies. I. A Four-zone Ionization Model for Very High-ionization Emission*

   https://doi.org/10.3847/1538-4357/ac141b  

   Berg, Danielle A. ; Chisholm, John ; Erb, Dawn K. ; Skillman, Evan D. ; Pogge, Richard W. ; Olivier, Grace M. ( November 2021 , The Astrophysical Journal)

   Abstract Stellar population models produce radiation fields that ionize oxygen up to O +2 , defining the limit of standard H ii region models (<54.9 eV). Yet, some extreme emission-line galaxies, or EELGs, have surprisingly strong emission originating from much higher ionization potentials. We present UV HST/COS and optical LBT/MODS spectra of two nearby EELGs that have very high-ionization emission lines (e.g., He ii λλ 1640,4686 C iv λλ 1548,1550, [Fe v ] λ 4227, [Ar iv ] λλ 4711,4740). We define a four-zone ionization model that is augmented by a very high-ionization zone, as characterized by He +2 (>54.4 eV). The four-zone model has little to no effect on the measured total nebular abundances, but does change the interpretation of other EELG properties: we measure steeper central ionization gradients; higher volume-averaged ionization parameters; and higher central T e , n e , and log U values. Traditional three-zone estimates of the ionization parameter can underestimate the average log U by up to 0.5 dex. Additionally, we find a model-independent dichotomy in the abundance patterns, where the α /H abundances are consistent but N/H, C/H, and Fe/H are relatively deficient, suggesting these EELGs are α /Fe-enriched by more than three times. However, there still is a high-energy ionizing photon production problem (HEIP 3 ). Even for such α /Fe enrichment and very high log U s, photoionization models cannot reproduce the very high-ionization emission lines observed in EELGs. 

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5. Fast methods for tracking grain coagulation and ionization: II. Extension to thermal ionization

   https://doi.org/10.1051/0004-6361/202142551  

   Marchand, P. ; Guillet, V. ; Lebreuilly, U. ; Mac Low, M.-M. ( October 2022 , Astronomy & Astrophysics)

   Thermal ionization is a critical process at temperatures T  > 10 3 K, particularly during star formation. An increase in ionization leads to a decrease in nonideal magnetohydrodynamics (MHD) resistivities, which has a significant impact on protoplanetary disks and protostar formation. We developed an extension of the fast computational ionization method presented in our recent paper to include thermal ionization. The model can be used to inexpensively calculate the density of ions and electrons and the electric charge of each size of grains for an arbitrary size distribution. This tool should be particularly useful for the self-consistent calculation of nonideal MHD resistivities in multidimensional simulations, especially of protostellar collapse and protoplanetary disks. 

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