Intramolecular charge transfer excitation induced by CH3O substitution in the 3-methoxy-1-propoxy radical. Issue 4 (21st January 2021)

• Record Type: Journal Article
• Authors: Xue, Junfei; Qin, Tai; Zu, Lily
• Is Part Of: Physical chemistry chemical physics. Volume 23:Issue 4(2020)
• Page Start: 2586
• Page End: 2593
• Publication Date: 2021-01-21
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.3
• DOI: 10.1039/d0cp06094a
• Languages: English
• ISSNs: 1463-9076

Abstract

Abstract : The charge-transfer excited state of 3-methoxy-1-propoxy has a conical intersection with the CO excited state, which changes its LIF spectrum. Abstract : The oxy-substituted alkoxy radicals are generated from the oxidation of ethers. Their degradation path affects ozone production and the formation of the secondary organic aerosol in the atmosphere. In this work, three alkoxy radicals with methoxy (CH3 O) substitution at β, γ, and δ carbon are studied using laser-induced fluorescence (LIF) spectroscopy and theoretical calculation methods. A charge transfer (CT) excited state induced by the CH3 O substitution is identified to be because of the intramolecular electron transfer from the C–O–C p orbital to the radical O p orbital. Comparison of the structure and CT transition strength between GGt and TTt conformers of the 3-methoxy-1-propoxy radical (CH3 OCH2 CH2 CH2 O) suggests that this long-range charge transfer effect is mainly a through-bond interaction. The CT excited state of CH3 OCH2 CH2 CH2 O has a conical intersection with the CO σ → O p excited state, which, hence, changes the LIF spectrum of the radical. Only the decomposition product HCHO was observed in the LIF spectrum of β substituted radical CH3 OCH2 CH2 O. For δ substituted radical CH3 OCH2 CH2 CH2 CH2 O, the substitution effect on the radical stability is negligible and its LIF spectrum is close to that of unsubstituted alkoxy radicals. The results provide information for understanding the degradation chemistry of oxygenated hydrocarbon molecules in the atmosphere.