Positive and Negative Photoion Spectroscopy Study of Monochlorothiophenes
journal contributionposted on 13.10.2011 by Yun-Feng Xu, Shan Xi Tian, Liuli Chen, Fu-Yi Liu, Liusi Sheng
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Photolysis dynamics of monochlorothiophenes (2- and 3-chlorothiophenes) is investigated using positive and negative photoion mass spectrometry combined with the synchrotron vacuum ultraviolet radiation. A dozen of the daughter cations are observed in the time-of-flight mass spectra, and their appearance energies are determined by the photoion efficiency spectroscopy measurements. At the energetic threshold, the concerted process rather than a stepwise reaction for C4H3SCl+ → C2HSCl+ + C2H2 and the ring-open isomers of the dehydrogenated thiophene cations (C4H3S+ and C4H2S+) formed in C4H3SCl+ → C4H3S+ + Cl and C4H2S+ + HCl are proposed on the basis of the B3LYP/6-311+G(3df,3pd) calculations. The chlorine anion (Cl–) is observed as the product of the photoion-pair dissociations in the energy range of 10.70–22.00 eV. A set of valence-to-Rydberg state transitions 12a′ → np (n = 6, 7, 8, 9, 10, etc.) and several series of vibrational excitations are tentatively assigned in the Cl– spectrum of 2-chlorothiophene in the lower energy range of 10.90–12.00 eV.