| Title: |
Quasi-symmetry effects in the threshold photoelectron spectrum of methyl isocyanate. |
| Authors: |
Harper, Oliver J.1, Coudert, Laurent H.1 laurent.coudert@u-psud.fr, Loison, Jean-Christophe2, Gans, Bérenger1, Douin, Stéphane1, Garcia, Gustavo A.3, Guillemin, Jean-Claude4, Boyé-Péronne, Séverine1 |
| Source: |
Journal of Chemical Physics. 8/21/2020, Vol. 153 Issue 7, p074308-1-074308-13. 13p. |
| Subject Terms: |
*PHOTOELECTRON spectra, *ELECTRON cloud effect, *SYNCHROTRON radiation, *IONIZATION energy, *METHYL groups, *PHOTOELECTRONS |
| Abstract: |
The vacuum-ultraviolet threshold photoelectron spectrum of methyl isocyanate CH3NCO has been recorded from 10.4 eV to 12 eV using synchrotron radiation and a coincidence technique allowing for a mass-discrimination of the photoelectron signal. A significant improvement is achieved over previous investigations as this experimental setup leads to a much more resolved spectrum. Ten sharp peaks and a broad feature spanning 1.2 eV were recorded. This spectrum consists of X̃+ 2A″←X̃¹A′ and Ã+ 2A′←X̃ ¹A′ ionizing transitions. For the former, the adiabatic ionization energy was determined experimentally to be 10.596(6) eV; for the latter, its value was estimated to be 10.759(50) eV. Seven sharp peaks could be assigned to vibrational modes of the cation X̃+ 2A″ and neutral X̃¹A′ ground electronic states involving only the NCO group atoms. Theoretical modeling of the threshold photoelectron spectrum has proven difficult as methyl isocyanate is a non-rigid molecule displaying large amplitude internal rotation of the methyl group and ∠CNC bending mode, leading to the quasi-symmetry. With the help of ab initio calculations, a theoretical model in which these two large amplitude motions are included in addition to the five small amplitude vibrational modes involving NCO group atoms is proposed. Comparison with the experimental spectrum shows that the broad feature and the strongest peak line positions are well accounted for; their intensities are also fairly well reproduced after adjusting a few parameters. [ABSTRACT FROM AUTHOR] |
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| Database: |
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