Photodissociation of Sodium Iodide Clusters Doped with Small Hydrocarbons

Abstract

Marine aerosols consist of a variety of compounds and play an important role in many atmospheric processes. In the present study, sodium iodide clusters with their simple isotope pattern serve as model systems for laboratory studies to investigate the role of iodide in the photochemical processing of sea‐salt aerosols. Salt clusters doped with camphor, formate and pyruvate are studied in a Fourier transform ion cyclotron resonance mass spectrometer (FT‐ICR MS) coupled to a tunable laser system in both UV and IR range. The analysis is supported by ab initio calculations of absorption spectra and energetics of dissociative channels. We provide quantitative analysis of IRMPD measurements by reconstructing one‐photon spectra and comparing them with the calculated ones. While neutral camphor is adsorbed on the cluster surface, the formate and pyruvate ions replace an iodide ion. The photodissociation spectra revealed several wavelength‐specific fragmentation pathways, including the carbon dioxide radical anion formed by photolysis of pyruvate. Camphor and pyruvate doped clusters absorb in the spectral region above 290 nm, which is relevant for tropospheric photochemistry, leading to internal conversion followed by intramolecular vibrational redistribution, which leads to decomposition of the cluster. Potential photodissociation products of pyruvate in the actinic region may be formed with a cross section of <2×10−20 cm2, determined by the experimental noise level.

Infrared Spectroscopy of Size‐Selected Hydrated Carbon Dioxide Radical Anions CO2.−(H2O)n (n=2–61) in the C−O Stretch Region

“…The number of photons that are needed to evaporate a water molecule ranges from one to three, as discussed in the Supporting Information (Figure SI‐10) . For the presentation of a realistic spectrum that accounts for laser energy and irradiation time, the single photon cross‐section σ is calculated by a modified Lambert–Beer's law: …”

Decomposition of Copper Formate Clusters: Insight into Elementary Steps of Calcination and Carbon Dioxide Activation

“…[28] Heating during calcination is simulated via vibrational excitation of asymmetric CÀ O stretching vibrations, with tunable IR light provided by an EKSPLA NT273-XIR optical parametric oscillator. [29] The change in the mass to charge ratio upon decomposition induced by Infrared Multiple Photon Dissociation (IRMPD) is measured and followed as a function of time. Using Collision Induced Dissociation (CID) in addition to ESI, reaction intermediates like Cu(I) m (HCO 2 ) m + 1 À (m = 1, 2) were produced and investigated individually.…”

Evidence for lactone formation during infrared multiple photon dissociation spectroscopy of bromoalkanoate doped salt clusters

“…S1 . IR absorption cross sections are derived by assuming sequential photon absorption following first-order kinetics, as described in detail before, 59 not considering radiative cooling. The contribution of ambient black-body infrared radiative dissociation (BIRD) 63 was taken into account as much as possible.…”

“… 54 We have recently investigated the IR induced decomposition of copper formate, 55 , 56 and measured IRMPD spectra of CO 2 ∙– (H 2 O) n and Co(CO 2 )(H 2 O) n − . 57 , 58 Of particular interest to the present work, however, are our recent studies on salt clusters doped with organic molecules, where we used IRMPD to elucidate structural properties 59 , 60 and UV excitation to analyze the influence of the salt environment on glyoxylate photochemistry. 61 …”