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1. Non-equilibrium dynamics at the gas–liquid interface: State-resolved studies of NO evaporation from a benzyl alcohol liquid microjet

   https://doi.org/10.1063/5.0143254  

   Ryazanov, Mikhail; Nesbitt, David J. (April 2023, The Journal of Chemical Physics)

   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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2. Ultraviolet Excitation of M-O ₂ (M = Phenalenone, Fluorenone, Pyridine, & Acridine) Complexes Resulting in ¹ O ₂

   https://doi.org/10.1021/acs.jpca.4c00143  

   Parsons, Bradley F.; Hulce, Martin R.; Ackerman, John R.; Reardon, Kylie A.; Pappas, Emerson S.; Kettler, Lauren E. (April 2024, The Journal of Physical Chemistry A)

   In our experiment, a trace amount of an organic molecule (M = 1H-phenalen-1-one, 9-fluorenone, pyridine, or acridine) was seeded into a gas mix consisting of 3% O₂ with a rare gas buffer (He or Ar) and then supersonically expanded. We excited the resulting molecular beam with ultraviolet light at either 355 nm (1H-phenalen-1-one, 9-fluorenone, or acridine) or 266 nm (pyridine) and used resonance enhanced multiphoton ionization (REMPI) spectroscopy to probe for formation of O₂ in the a ¹Δ_g state, ¹O₂. For all systems, the REMPI spectra demonstrates that ultraviolet excitation results in formation of ¹O₂ and the oxygen product is confirmed to be in the ground vibrational state and with an effective rotational temperature below 80 K. We then recorded the velocity map ion image of the ¹O₂ product. From the ion images we determined the center-of-mass translational energy distribution, P(E_T), assuming photodissociation of a bimolecular M-O₂ complex. We also report results from electronic structure calculations that allow for a determination of the M-O₂ ground state binding energy. We use the complex binding energy, the energy to form ¹O₂, and the adiabatic triplet energy for each organic molecule to determine the available energy following photodissociation. For dissociation of a bimolecular complex, this available energy may be partitioned into either center-of-mass recoil or internal degrees of freedom of the organic moiety. We use the available energy to generate a Prior distribution, which predicts statistical energy partitioning during dissociation. For low available energies, less than 0.2 eV, we find the statistical prediction is in reasonable agreement with the experimental observations. However, at higher available energies the experimental distribution is biased to lower center-of-mass kinetic energies compared with the statistical prediction, which suggests the complex undergoes vibrational predissociation. 

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3. Rate coefficients for rotational state-to-state transitions in H ₂ O + H ₂ O collisions for cometary and planetary applications, as predicted by mixed quantum-classical theory

   https://doi.org/10.1051/0004-6361/202245699  

   Mandal, Bikramaditya; Babikov, Dmitri (March 2023, Astronomy & Astrophysics)

   Aims. We present new calculations of collision cross sections for state-to-state transitions between the rotational states in an H 2 O + H 2 O system, which are used to generate a new database of collisional rate coefficients for cometary and planetary applications. Methods. Calculations were carried out using a mixed quantum-classical theory approach that is implemented in the code MQCT. The large basis set of rotational states used in these calculations permits us to predict thermally averaged cross sections for 441 transitions in para- and ortho-H 2 O in a broad range of temperatures. Results. It is found that all state-to-state transitions in the H 2 O + H 2 O system split into two well-defined groups, one with higher cross-section values and lower energy transfer, which corresponds to the dipole-dipole driven processes. The other group has smaller cross sections and higher energy transfer, driven by higher-order interaction terms. We present a detailed analysis of the theoretical error bars, and we symmetrized the state-to-state transition matrixes to ensure that excitation and quenching processes for each transition satisfy the principle of microscopic reversibility. We also compare our results with other data available from the literature for H 2 O + H 2 O collisions. 

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4. A Highly Water‐ and Air‐Stable Iron‐Containing MRI Contrast Agent Sensor for H ₂ O ₂

   https://doi.org/10.1002/chem.202201179  

   Karbalaei, Sana; Franke, Alicja; Jordan, Aubree; Rose, Cayla; Pokkuluri, P_Raj; Beyers, Ronald_J; Zahl, Achim; Ivanović‐Burmazović, Ivana; Goldsmith, Christian_R (June 2022, Chemistry – A European Journal)

   Abstract A highly water‐ and air‐stable Fe(II) complex with the quinol‐containing macrocyclic ligand H₄qp4 reacts with H₂O₂to yield Fe(III) complexes with less highly chelating forms of the ligand that have either one or twopara‐quinones. The reaction increases theT₁‐weighted relaxivity over four‐fold, enabling the complex to detect H₂O₂using clinical MRI technology. The iron‐containing sensor differs from its recently characterized manganese analog, which also detects H₂O₂, in that it is the oxidation of the metal center, rather than the ligand, that primarily enhances the relaxivity. 

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5. H ₃ ⁺ absorption and emission in local (U)LIRGs with JWST/NIRSpec: Evidence for high H ₂ ionization rates

   https://doi.org/10.1051/0004-6361/202451741  

   Pereira-Santaella, Miguel; González-Alfonso, Eduardo; García-Bernete, Ismael; Donnan, Fergus R; Santa-Maria, Miriam G; Goicoechea, Javier R; Lamperti, Isabella; Perna, Michele; Rigopoulou, Dimitra (September 2024, Astronomy & Astrophysics)

   We study the 3.4 − 4.4 μm fundamental rovibrational band of H₃⁺, a key tracer of the ionization of the molecular interstellar medium (ISM), in a sample of 12 local (d < 400 Mpc) (ultra)luminous infrared galaxies ((U)LIRGs) observed with JWST/NIRSpec. TheP,Q, andRbranches of the band are detected in 13 out of 20 analyzed regions within these (U)LIRGs, which increases the number of extragalactic H₃⁺detections by a factor of 6. For the first time in the ISM, the H₃⁺band is observed in emission; we detect this emission in three regions. In the remaining ten regions, the band is seen in absorption. The absorptions are produced toward the 3.4 − 4.4 μm hot dust continuum rather than toward the stellar continuum, indicating that they likely originate in clouds associated with the dust continuum source. The H₃⁺band is undetected in Seyfert-like (U)LIRGs where the mildly obscured X-ray radiation from the active galactic nuclei might limit the abundance of this molecule. For the detections, the H₃⁺abundances,N(H₃⁺)/N_H = (0.5 − 5.5)×10⁻⁷, imply relatively high ionization rates,ζ_H2, of between 3 × 10⁻¹⁶and > 4 × 10⁻¹⁵s⁻¹, which are likely associated with high-energy cosmic rays. In half of the targets, the absorptions are blueshifted by 50–180 km s⁻¹, which is lower than the molecular outflow velocities measured using other tracers such as OH 119 μm or rotational CO lines. This suggests that H₃⁺traces gas close to the outflow-launching sites before it has been fully accelerated. We used nonlocal thermodynamic equilibrium models to investigate the physical conditions of these clouds. In seven out of ten objects, the H₃⁺excitation is consistent with inelastic collisions with H₂in warm translucent molecular clouds (T_kin ∼ 250–500 K andn(H₂) ∼10^2 − 3cm⁻³). In three objects, dominant infrared pumping excitation is required to explain the absorptions from the (3,0) and (2,1) levels of H₃⁺detected for the first time in the ISM. 

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