Vacuum Ultraviolet Photoionization of C3

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• 作者：Christophe Nicolas ; Jinian Shu ; Darcy S. Peterka ; Majdi Hochlaf ; Lionel Poisson ; Stephen R. Leone ; and Musahid Ahmed
• 刊名：Journal of the American Chemical Society
• 出版年：2006
• 出版时间：January 11, 2006
• 年：2006
• 卷：128
• 期：1
• 页码：220 - 226
• 全文大小：119K
• 年卷期：v.128,no.1(January 11, 2006)
• ISSN：1520-5126

文摘

Photoionization efficiency (PIE) curves for C₃ molecules produced by laser ablation are measuredfrom 11.0 to 13.5 eV with tunable vacuum ultraviolet undulator radiation. A step in the PIE curve versusphoton energy, obtained with N₂ as the carrier gas, supports the conclusion of very effective cooling of C₃to its linear ¹s/gifchars/Sigma.gif" BORDER=0 >_g⁺ ground state. The second step observed in the PIE curve versus photon energy could bethe first experimental evidence of the C₃⁺(²s/gifchars/Sigma.gif" BORDER=0 >_g⁺) excited state. The experimental results, complemented byab initio calculations, suggest a state-to-state vertical ionization energy of 11.70 ± 0.05 eV between theC₃(s/entities/Xtilde.gif">¹s/gifchars/Sigma.gif" BORDER=0 >_g⁺) and the C₃⁺(s/entities/Xtilde.gif">²s/gifchars/Sigma.gif" BORDER=0 >_u⁺) states. An ionization energy of 11.61 ± 0.07 eV between the neutral andionic ground states of C₃ is deduced using the data together with our calculations. Accurate ab initiocalculations are performed for both linear and bent geometries on the lowest doublet electronic states ofC₃⁺ using Configuration Interaction (CI) approaches and large basis sets. These calculations confirm thatC₃⁺ is bent in its electronic ground state, which is separated by a small potential barrier from the ²s/gifchars/Sigma.gif" BORDER=0 >_u⁺minimum. The gradual increase at the onset of the PIE curve suggests a geometry change between theground neutral and cationic states. The energies between several doublet states of the ion are theoreticallydetermined to be 0.81, 1.49, and 1.98 eV between the ²s/gifchars/Sigma.gif" BORDER=0 >_u⁺ and the ²s/gifchars/Sigma.gif" BORDER=0 >_g⁺, ²s/gifchars/Pi.gif" BORDER=0 >_u, ²s/gifchars/Pi.gif" BORDER=0 >_g excited states of C₃⁺,respectively.