title: Ground and low-lying excited states of propadienylidene (H2C=C=C:) obtained by negative ion photoelectron spectroscopy.
abstract: A joint experimental-theoretical study has been carried out on electronic states of propadienylidene (H(2)CCC), using results from negative-ion photoelectron spectroscopy. In addition to the previously characterized X(1)A(1) electronic state, spectroscopic features are observed that belong to five additional states: the low-lying ã(3)B(1) and b(3)A(2) states, as well as two excited singlets, Ã(1)A(2) and B(1)B(1), and a higher-lying triplet, c(3)A(1). Term energies (T(0), in cm(-1)) for the excited states obtained from the data are: 10,354±11 (ã(3)B(1)); 11,950±30 (b(3)A(2)); 20,943±11 (c(3)A(1)); and 13,677±11 (Ã(1)A(2)). Strong vibronic coupling affects the Ã(1)A(2) and B(1)B(1) states as well as ã(3)B(1) and b(3)A(2) and has profound effects on the spectrum. As a result, only a weak, broadened band is observed in the energy region where the origin of the B(1)B(1) state is expected. The assignments here are supported by high-level coupled-cluster calculations and spectral simulations based on a vibronic coupling Hamiltonian. A result of astrophysical interest is that the present study supports the idea that a broad absorption band found at 5450 Å by cavity ringdown spectroscopy (and coincident with a diffuse interstellar band) is carried by the B(1)B(1) state of H(2)CCC.
authors.affiliation: Institute for Theoretical Chemistry, Department of Chemistry and Biochemistry, The University of Texas at Austin, Austin, Texas 78712, USA.
authors.forename: John F
authors.initials: JF
authors.lastname: Stanton
authors.forename: Etienne
authors.initials: E
authors.lastname: Garand
authors.forename: Jongjin
authors.initials: J
authors.lastname: Kim
authors.forename: Tara I
authors.initials: TI
authors.lastname: Yacovitch
authors.forename: Christian
authors.initials: C
authors.lastname: Hock
authors.forename: Amanda S
authors.initials: AS
authors.lastname: Case
authors.forename: Elisa M
authors.initials: EM
authors.lastname: Miller
authors.forename: Yu-Ju
authors.initials: YJ
authors.lastname: Lu
authors.forename: Kristen M
authors.initials: KM
authors.lastname: Vogelhuber
authors.forename: Scott W
authors.initials: SW
authors.lastname: Wren
authors.forename: Takatoshi
authors.initials: T
authors.lastname: Ichino
authors.forename: John P
authors.initials: JP
authors.lastname: Maier
authors.forename: Robert J
authors.initials: RJ
authors.lastname: McMahon
authors.forename: David L
authors.initials: DL
authors.lastname: Osborn
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Neumark
authors.forename: W Carl
authors.initials: WC
authors.lastname: Lineberger