Electron-Withdrawing Effects in the Photodissociation of CH2ICl To Form CH2Cl Radical, Simultaneously Viewed Through the Carbon K and Chlorine L2,3 X-ray Edges
A fundamental chlorine-containing radical, CH2Cl, is generated by the ultrafast photodissociation of CH2ICl at 266 nm and studied at both the carbon K edge (~284 eV) and chlorine L2,3 edge (~200 eV) by femtosecond X-ray transient absorption spectroscopy. The electronic structure of CH2Cl radical is characterized by a prominent new carbon 1s X-ray absorption feature at lower energy, resulting from a transition to the half-filled frontier carbon 2p orbital (singly occupied molecular orbital of the radical; SOMO). Shifts of other core-to-valence absorption features upon photodissociation of CH2ICl to yield ·CH2Cl indicate changes in the energies of core-level transitions of carbon and chlorine to the σ*(C-Cl) valence orbital. When the C-I bond breaks, loss of the electron-withdrawing iodine atom donates electron density back to carbon and shields the carbon 1s core level, resulting in a ~0.8 eV red shift of the carbon 1s to σ*(C-Cl) transition. Meanwhile, the 2p inner shell of the chlorine atom in the radical is less impacted by the iodine atom removal, as demonstrated by the observation of a ~0.6 eV blue shift of the transitions at the chlorine L2,3 edges, mainly due to the stronger C-Cl bond and the increased energy of the σ* (C-Cl) orbital. The results suggest that the shift in the carbon 1s orbital is greater than the shift in the σ* (C-Cl) orbital upon going from the closed-shell molecule to the radical. Ab initio calculations using the equation of motion coupled-cluster theory establish rigorous assignment and positions of the X-ray spectral features in the parent molecule and the location of the SOMO in the CH2Cl radical.
- Research Organization:
- Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES)
- Grant/Contract Number:
- AC02-05CH11231
- OSTI ID:
- 1542330
- Journal Information:
- Journal of the American Chemical Society, Vol. 140, Issue 41; ISSN 0002-7863
- Publisher:
- American Chemical Society (ACS)Copyright Statement
- Country of Publication:
- United States
- Language:
- English
Web of Science
Probing ultrafast C–Br bond fission in the UV photochemistry of bromoform with core-to-valence transient absorption spectroscopy
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journal | September 2019 |
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