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Rydberg or Valence? The Long‐Standing Question in the UV Absorption Spectrum of 1,1′‐Bicyclohexylidene
Author(s) -
PérezHernández Guillermo,
González Leticia,
SerranoAndrés Luis
Publication year - 2008
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.200800454
Subject(s) - rydberg formula , excited state , chemistry , atomic physics , valence (chemistry) , absorption spectroscopy , photoexcitation , excitation , complete active space , molecular physics , physics , density functional theory , ionization , optics , computational chemistry , quantum mechanics , organic chemistry , basis set , ion
Abstract The electronic excited states of the olefin 1,1′‐bicylohexylidene (BCH) are investigated using multiconfigurational complete active space self‐consistent‐field second order perturbation theory in its multi‐state version (MS‐CASPT2). Our calculations undoubtedly show that the bulk of the intensity of the two unusually intense bands of the UV absorption of BCH measured with maxima at 5.95 eV and 6.82 eV in the vapor phase are due to a single π π * valence excitation. Sharp peaks reported in the vicinity of the low‐energy feature in the gas phase correspond to the beginning of the π3s R Rydberg series. By locating the origin of the π π * band at 5.63 eV, the intensity and broadening of the observed bands and their presence in solid phase is explained as the vibrational structure of the valence π π * transition, which underlies the Rydberg manifold as a quasi‐continuum.