Electronic States of Aromatic Hydrocarbons: The Franck-Condon Principle and Geometries in Excited States

摘要: It is suggested that electronic transitions in aromatic hydrocarbons can profitably be characterized by a quantity R, where R2 the sum of squares bond length changes accompanying transition. R determines, via Franck-Condon principle, distribution intensity within vibrational envelope In polycyclic aromatics, values extracted from solution spectra, if intervals about 1400 cm-1 which commonly separate peaks are interpreted as defining quasi-progressions skeletal displacement vibration. Values so determined compared with computed orders excited states, using wave-functions Pariser. Such comparisons made for benzene, naphthalene, azulene, and anthracene. Agreement good. The calculated tabulated. an Appendix, angles rings on assumption observed minimize σ-bond strain energy. Angles ground states naphthalene anthracene, two naphthalene. state geometries deduced depicted.