title: Towards experimental determination of conical intersection properties: a twin state based comparison with bound excited states.
abstract: The energy and approximate structure of certain S(0)/S(1) conical intersections (CI) are shown computationally to be deducible from those of two bound states: the first triplet (T(1)), which is iso-energetic with the CI, and the second excited singlet state (S(2)). This is demonstrated for acepentalene (I) and its perfluoro derivative (II) using the twin state concept for three states systems and based on the fact that the triplet T(1) is almost degenerate with the CI. The stable S(2) (C(3v) configuration) state exhibits unusual exaltation of Jahn-Teller active degenerate mode-ν(JT) = 2058 cm(-1) (∼500 cm(-1) higher than analogous e-mode of the symmetric (C(3v)) T(1) and the dianion I(-2) or any C-C vibration of the Jahn-Teller distorted (C(s)) ground state minimum). The acepentalene molecule, whose rigid structure and possibility to attain the relatively high symmetry C(3v) configuration, is a particularly suitable candidate for this purpose.
authors.affiliation: Institute of Chemistry and the Farkas Center for Light Induced Processes, The Hebrew University of Jerusalem, 91904 Jerusalem, Israel. shmuel@fh.huji.ac.il
authors.forename: Shmuel
authors.initials: S
authors.lastname: Zilberg
authors.forename: Yehuda
authors.initials: Y
authors.lastname: Haas