title: Structure of pyridazine in the S1 state: experiment and theory.
abstract: The molecular structure of pyridazine in the first electronically excited state (S(1)) is deduced from the combined use of resonance-enhanced two-photon ionization and mass-analyzed threshold ionization spectroscopic methods. The equation-of-motion coupled-cluster single and double (EOM-CCSD) calculation gives the distorted planar geometry for the most stable structure of the S(1) pyridazine. The symmetry constraint of C(2v) is relaxed to that of C(s), and consequently many in-plane vibrational modes are found to be optically active in both S(1)-S(0) and D(0)-S(1) excitation spectra, being appropriately assigned from the comparison of their frequencies with ab initio values. This indicates that the S(1)-S(0) excitation is partially localized, and provides an alternative explanation for the long-standing spectroscopic puzzle in S(1) pyridazine.
authors.affiliation: Department of Chemistry and School of Molecular Sciences (BK21), KAIST, Daejeon 301-750, Korea.
authors.forename: Doo-Sik
authors.initials: DS
authors.lastname: Ahn
authors.forename: Kyo-Won
authors.initials: KW
authors.lastname: Choi
authors.forename: Sun Jong
authors.initials: SJ
authors.lastname: Baek
authors.forename: Young S
authors.initials: YS
authors.lastname: Choi
authors.forename: Sungyul
authors.initials: S
authors.lastname: Lee
authors.forename: Heechol
authors.initials: H
authors.lastname: Choi
authors.forename: Kyoung Koo
authors.initials: KK
authors.lastname: Baeck
authors.forename: Sang Kyu
authors.initials: SK
authors.lastname: Kim