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Title:Spectroscopically Identifying From Gas-phase Reactions Of Distonic Benzonitrileh+ Radical Ions In An Ion-trap Mass Spectrometer
Author(s):Shiels, Oisin J.
Contributor(s):Trevitt, Adam J.; Blanksby, Stephen J.; Silva, Gabriel da; Kelly, P. D.; Marlton, Samuel
Subject(s):Instrument/Technique Demonstration
Abstract:Benzonitrile was recently detected in the interstellar medium and currently remains the largest aromatic molecule identified. Subsequent reactions with benzonitrile and related cations are good candidates to form polycyclic aromatic molecules (PAHs), potentially contributing to the UIB band. Previous investigations into the reactions of the three distonic radical isomers of the benzonitrile cation with ethylene and acetylene have identified that these reactions are barrierless and should proceed within the ultra-low temperatures of the interstellar medium – but what products do these reactions form? Expanding on this previous work, the reactions of the 2-dehydrobenzonitrileH$^+$ distonic radical cation + propyne (CHCCH$_3$) were investigated using a combination of computational and experimental techniques. Experimental investigations, performed within the room temperature linear ion-trap reveal that multiple product channels arise, ranging from: C$_{3}$H$_{4}$ addition [M + 40]$^{+}$, C$_{2}$H$_{3}$ loss following C$_3$H$_4$ addition [M + 40 - 27]$^{+}$, double C$_3$H$_4$ addition [M + 40 + 40]$^{+}$, and H-atom loss following secondary C$_{3}$H$_{4}$ addition [M + 40 + 40 - 1]$^{+}$. Targeting the double C$_3$H$_4$ addition, calculations suggest that two tri-cyclic PAH isomers are energetically favourable products. To assign these putative tri-cyclic PAHs, photodissociation action spectroscopy experiments were performed to structurally characterise these secondary addition products. Exploiting the ion trap, these reaction products can be selectively isolated, stored and then subjected to tunable laser photons. Photodissociation action spectra are recorded by tracking the yield of photoproduct ions as a function of photon energy. Spectra are compared to Franck-Condon simulations and good matches are found with the two tri-cylcic PAH products. These experiments allow us to definitely assign the reaction products, giving us a new measurement to benchmark calculations against.
Issue Date:2021-06-23
Publisher:International Symposium on Molecular Spectroscopy
Genre:Conference Paper / Presentation
Date Available in IDEALS:2021-09-24

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