Journal of Computer Chemistry, Japan
Online ISSN : 1347-3824
Print ISSN : 1347-1767
ISSN-L : 1347-1767
Letters (Selected Paper)
Assignment of the First 275-nm Absorption System of Phenyl Isocyanate by Quantum-Chemistry Calculation
Yuto NAGANUMADaisuke ISHIBASHIKatsuhiko OKUYAMA
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2021 Volume 20 Issue 4 Pages 129-131

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Abstract: Electronic spectra for the first 275-nm absorption system of phenyl isocyanate observed in a room temperature and in a jet were assigned with an assistance of quantum-chemistry calculation. All vibronic bands in a jet were diffuse with a width of 18 cm−1, indicating the lower limit of the life time was 204 fs. A suitable pair of a theoretical method and a basis set was selected among combinations of B3LYP, CAM-B3LYP, and MP2 and 18 kinds of basis sets on the basis of molecular-orbital energies and the rotational constant spectroscopically observed. B3LYP/cc-pVTZ and B3YP/aug-cc-pVDZ gave us good results. Time-dependent calculation was performed by two pairs. It was found out that the 275-nm absorption system was assigned as the first ππ* and third excited state and that twonπ* states with a very small oscillator strength were lying in the infrared and visible region. The fast relaxation process observed in a jet was due to an internal conversion to two nπ* states.

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