Negative ion photoelectron spectra of ISO3–, IS2O3–, and IS2O4– intermediates formed in interfacial reactions of ozone and iodide/sulfite aqueous microdroplets

Abstract

Three short-lived, anionic intermediates, ISO, ISO, and ISO, are detected during reactions between ozone and aqueous iodine/sulfur oxide microdroplets. These species may play an important role in ozone-driven inorganic aerosol formation; however their chemical properties remain largely unknown. This is the issue addressed in this work using negative ion photoelectron spectroscopy (NIPES) and ab initio modeling. The NIPE spectra reveal that all of the three anionic species are characterized by high adiabatic detachment energies (ADEs) - 4.62 ± 0.10, 4.52 ± 0.10, and 4.60 ± 0.10 eV for ISO, ISO, and ISO, respectively. Vibrational progressions with frequencies assigned to the S-O symmetric stretching modes are discernable in the ground state transition features. Density functional theory calculations show the presence of several low-lying isomers involving different bonding scenarios. Further analysis based on high level CCSD(T) calculations reveal that the lowest energy structures are characterized by the formation of I-S and S-S bonds and can be structurally viewed as SO linked with I, IS, and ISO for ISO, ISO, and ISO, respectively. The calculated ADEs and vertical detachment energies are in excellent agreement with the experimental results, further supporting the identified minimum energy structures. The obtained intrinsic molecular properties of these anionic intermediates and neutral radicals should be useful to help understand their photochemical reactions in the atmosphere.

Molecular Specificity and Proton Transfer Mechanisms in Aerosol Prenucleation Clusters Relevant to New Particle Formation

“…We have studied several atmospherically important inorganic ions and their hydrates, including halogen oxides BrO 2,3 – and IO 2–4 – , iodine sulfur oxides ISO 3 – , IS 2 O 3 – , and IS 2 O 4 – , iodate clusters IO 3 – (HIO 3 ), IO 3 – (H 2 O) n , and hydrated bicarbonate clusters HCO 3 – (H 2 O) n . Detailed geometric and electronic structures have been unveiled for these ions and their corresponding neutrals to better understand their photochemical reactions in the atmosphere.…”

Sulfuric acid and aromatic carboxylate clusters H2SO4·ArCOO−: Structures, properties, and their relevance to the initial aerosol nucleation

“…[8] We have been interested in characterizing the small pre-nucleation clusters relevant to NPF, especially organic acid containing clusters, by combining negative ion photoelectron spectroscopy (NIPES) and quantum chemical calculations. [30][31][32][33][34][35][36][37] For example, we have shown that succinic acid molecule, HO 2 C(CH 2 ) 2 CO 2 H, is capable of stabilizing the bisulfate ion HSO 4 − and its own conjugate base succinate ion, HO 2 C(CH 2 ) 2 CO 2 − , indicating significant thermodynamic advantage of organic molecules in promoting bisulfate clusters and organic aerosol particles formation. [30,34] Most recently, we have studied the deprotonated sulfuric acid-formic acid anionic cluster [H 2 SO 4 •HCOOH−H + ] − , and found that the charge delocalization accompanying formation of two strong hydrogen bonds is strong enough to compensate the proton affinity imbalance in forming H 2 SO 4 •HCOO − cluster.…”

Spectroscopic Signature of Proton Location in Proton Bound HSO4–·H+·X– (X = F, Cl, Br, and I) Clusters

“…In general, the agreement is reasonably good, particularly, the trend captured by calculations for X = Cl, Br, and I agrees excellently with the experiment (Figure ). We also simulated the density of states (DOS) spectra of the most stable and high lying isomers for each cluster to compare with the experimental spectra (Figure S3), based on theoretically generalized Koopmans’ theorem (GKT), , in which the observed spectral features can be viewed as originating from one electron removal from the occupied molecular orbitals of the anion (this method works particularly well for closed-shell species − ). In all cases, the simulated DOS spectra based on the most stable structures shown in Figure give better agreement with the experiments, further supporting our analysis.…”