Spectroscopic characterization of two peroxyl radicals during the O2-oxidation of the methylthio radical

Zhuang Wu,Joseph S Francisco,Bifeng Zhu,Xin Shao,Tarek Trabelsi,Lina Wang,Xiaoqing Zeng,Bo Lu

doi:10.1038/s42004-022-00637-z

Zhuang Wu, Joseph S Francisco + Show 6 more

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https://doi.org/10.1038/s42004-022-00637-z

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Abstract

The atmospheric oxidation of dimethyl sulfide (DMS) yields sulfuric acid and methane sulfonic acid (MSA), which are key precursors to new particles formed via homogeneous nucleation and further cluster growth in air masses. Comprehensive experimental and theoretical studies have suggested that the oxidation of DMS involves the formation of the methylthio radical (CH3S•), followed by its O2-oxidation reaction via the intermediacy of free radicals CH3SOx• (x = 1–4). Therefore, capturing these transient radicals and disclosing their reactivity are of vital importance in understanding the complex mechanism. Here, we report an optimized method for efficient gas-phase generation of CH3S• through flash pyrolysis of S-nitrosothiol CH3SNO, enabling us to study the O2-oxidation of CH3S• by combining matrix-isolation spectroscopy (IR and UV–vis) with quantum chemical computations at the CCSD(T)/aug-cc-pV(X + d)Z (X = D and T) level of theory. As the key intermediate for the initial oxidation of CH3S•, the peroxyl radical CH3SOO• forms by reacting with O2. Upon irradiation at 830 nm, CH3SOO• undergoes isomerization to the sulfonyl radical CH3SO2• in cryogenic matrixes (Ar, Ne, and N2), and the latter can further combine with O2 to yield another peroxyl radical CH3S(O)2OO• upon further irradiation at 440 nm. Subsequent UV-light irradiation (266 nm) causes dissociation of CH3S(O)2OO• to CH3SO2•, CH2O, SO2, and SO3. The IR spectroscopic identification of the two peroxyl radicals CH3SOO• and CH3S(O)2OO• is also supported by 18O- and 13C-isotope labeling experiments.

Highlights

The atmospheric oxidation of dimethyl sulfide (DMS) yields sulfuric acid and methane sulfonic acid (MSA), which are key precursors to new particles formed via homogeneous nucleation and further cluster growth in air masses
Dimethyl sulfide (DMS, CH3SCH3) is the most abundant biogenic volatile organic sulfur compound (VOSC) that is produced through enzymatic lysis of dimethylsulfoniopropionate (DMSP) in the oceans[1,2,3]
CH3SO3 can either dissociate (→ CH3 + SO3) or undergo hydrogen abstraction to furnish sulfuric acid (SO3 + H2O → H2SO4) and methane sulfonic acid (CH3SO3H, MSA)[9], respectively. Both acids are key precursors to new particles formed via homogeneous nucleation and subsequent cluster growth in air masses[13,14]

Summary

Introduction

The atmospheric oxidation of dimethyl sulfide (DMS) yields sulfuric acid and methane sulfonic acid (MSA), which are key precursors to new particles formed via homogeneous nucleation and further cluster growth in air masses. Dimethyl sulfide (DMS, CH3SCH3) is the most abundant biogenic volatile organic sulfur compound (VOSC) that is produced through enzymatic lysis of dimethylsulfoniopropionate (DMSP) in the oceans[1,2,3]. DMS plays a key role in the organosulfur cycle with an estimated annual flux of about 30 teragrams of sulfur in the atmosphere[4,5]. The removal of DMS under marine atmospheric boundary layer (MABL) conditions involves biological consumption, seaatmosphere exchange, and oxidation reactions. The atmospheric oxidation of DMS to condensable products contributes to the formation of secondary sulfate aerosols that affect Earth’s climate by scattering solar irradiation and simultaneously acting as cloud condensation nuclei (CCN)[6,7]. The details about the oxidation mechanism of DMS are of vital importance in understanding the interplay between atmospheric chemistry and climate change[8] The atmospheric oxidation of DMS can proceed through the OH-addition pathway (Fig. 1), resulting the stepwise formation of additional VOSCs dimethyl sulfoxide (DMSO, CH3S(O)CH3), and methanesulfinic acid (CH3S(O) OH)[15,16,17,18,19,20,21,22]

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