The umbrella motion of core-excited CH3 and CD3 methyl radicals

• An accurate experimental and theoretical study of the lowest core excitationof CH3 and CD3 methyl radicals is presented. The complexvibrational structure of the lowest band of the x-ray absorptionspectrum (XAS) is due to the large variation of themolecular geometry, which is planar in the ground state andpyramidal in the core-excited state. The XAS spectra of thetwo radicals were recorded at high resolution and assigned bytheoretical simulations of the spectra, taking into account the couplingof symmetrical stretching and symmetrical bending (umbrellalike) deformations of theradicals. An excellent agreement between experimental and theoretical spectral profilesallowed us to accurately characterize the vibrational structure of theelectronic transition. The similarities, as well as the differences, ofthe peculiar vibrational progression observed for the two radicals areexplained by the strong anharmonicity along the umbrella coordinate andby the isotopic variation, leading to a different probing ofthe double-well potential energy surface of the core excited stateduring the nuclear motion.

Nyckelord

excited states

free radicals

ground states

molecular configurations

organic compounds

potential energy surfaces

vibrational states

X-ray scattering

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