Non-Adiabatic Effects on Excited States of Vinylidene Observed with Slow Photoelectron Velocity-Map Imaging

详细信息    查看全文

• 作者：Jessalyn A. DeVineMarissa L. Weichman ; Xueyao ZhouJianyi Ma ; Bin JiangHua Guo ; Daniel M. Neumark
• 刊名：Journal of the American Chemical Society
• 出版年：2016
• 出版时间：December 21, 2016
• 年：2016
• 卷：138
• 期：50
• 页码：16417-16425
• 全文大小：603K
• ISSN：1520-5126

文摘

High-resolution slow photoelectron velocity-map imaging spectra of cryogenically cooled X̃²B₂ H₂CC^– and D₂CC^– in the region of the vinylidene triplet excited states are reported. Three electronic bands are observed and, with the assistance of electronic structure calculations and quantum dynamics on ab initio-based near-equilibrium potential energy surfaces, are assigned as detachment to the ³B₂ (T₁), b̃ ³A₂ (T₂), and à ¹A₂ (S₁) excited states of neutral vinylidene. This work provides the first experimental observation of the à singlet excited state of H₂CC. While regular vibrational structure is observed for the ã and à electronic bands, a number of irregular features are resolved in the vicinity of the b̃ band vibrational origin. High-level ab initio calculations suggest that this anomalous structure arises from a conical intersection between the ã and b̃ triplet states near the b̃ state minimum, which strongly perturbs the vibrational levels in the two electronic states through nonadiabatic coupling. Using the adiabatic electron affinity of H₂CC previously measured to be 0.490(6) eV by Ervin and co-workers [J. Chem. Phys. 1989, 91, 5974], term energies for the excited neutral states of H₂CC are found to be T₀(ã ³B₂) = 2.064(6), T₀(b̃ ³A₂) = 2.738(6), and T₀(à ¹A₂) = 2.991(6) eV.