Cooper Joseph C, Holland David M P, Ingle Rebecca A, Bonanomi Matteo, Faccialà Davide, De Oliveira Nelson, Abid Abdul R, Bachmann Julien, Bhattacharyya Surjendu, Borne Kurtis, Bosch Michael, Centurion Martin, Chen Keyu, Forbes Ruaridh J G, Lam Huynh V S, Odate Asami, Rudenko Artem, Venkatachalam Anbu S, Vozzi Caterina, Wang Enliang, Weber Peter M, Ashfold Michael N R, Kirrander Adam, Rolles Daniel
Physical and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, Oxford OX1 3QZ, United Kingdom.
STFC, Daresbury Laboratory, Warrington WA4 2DS, United Kingdom.
J Chem Phys. 2024 Feb 14;160(6). doi: 10.1063/5.0187707.
The absolute photoabsorption cross sections of norbornadiene (NBD) and quadricyclane (QC), two isomers with chemical formula C7H8 that are attracting much interest for solar energy storage applications, have been measured from threshold up to 10.8 eV using the Fourier transform spectrometer at the SOLEIL synchrotron radiation facility. The absorption spectrum of NBD exhibits some sharp structure associated with transitions into Rydberg states, superimposed on several broad bands attributable to valence excitations. Sharp structure, although less pronounced, also appears in the absorption spectrum of QC. Assignments have been proposed for some of the absorption bands using calculated vertical transition energies and oscillator strengths for the electronically excited states of NBD and QC. Natural transition orbitals indicate that some of the electronically excited states in NBD have a mixed Rydberg/valence character, whereas the first ten excited singlet states in QC are all predominantly Rydberg in the vertical region. In NBD, a comparison between the vibrational structure observed in the experimental 11B1-11A1 (3sa1 ← 5b1) band and that predicted by Franck-Condon and Herzberg-Teller modeling has necessitated a revision of the band origin and of the vibrational assignments proposed previously. Similar comparisons have encouraged a revision of the adiabatic first ionization energy of NBD. Simulations of the vibrational structure due to excitation from the 5b2 orbital in QC into 3p and 3d Rydberg states have allowed tentative assignments to be proposed for the complex structure observed in the absorption bands between ∼5.4 and 7.0 eV.
降冰片二烯（NBD）和四环烷（QC）是化学式为C₇H₈的两种同分异构体，它们在太阳能存储应用中引起了广泛关注。利用SOLEIL同步辐射设施的傅里叶变换光谱仪，测量了这两种异构体从阈值到10.8 eV的绝对光吸收截面。NBD的吸收光谱呈现出一些与向里德堡态跃迁相关的尖锐结构，叠加在几个归因于价电子激发的宽带上。尖锐结构在QC的吸收光谱中也有出现，不过不太明显。利用计算得到的NBD和QC电子激发态的垂直跃迁能量和振子强度，对一些吸收带进行了归属。自然跃迁轨道表明，NBD中的一些电子激发态具有混合的里德堡/价电子特征，而QC中的前十个激发单重态在垂直区域主要都是里德堡态。在NBD中，将实验中11B₁ - 11A₁（3sa₁ ← 5b₁）带中观察到的振动结构与弗兰克 - 康登和赫兹伯格 - 特勒模型预测的结构进行比较，需要对带起源和先前提出的振动归属进行修正。类似的比较促使对NBD的绝热第一电离能进行修正。对QC中从5b₂轨道激发到3p和3d里德堡态所产生的振动结构进行模拟，使得能够对在约5.4至7.0 eV吸收带中观察到的复杂结构提出初步归属。
