title: First observation of the 3Πg3 state of C2: Born-Oppenheimer breakdown.
abstract: The 33Πgstate of the dicarbon molecule, C2, has been identified for the first time by a combination of resonant ionization spectroscopy, mass spectrometry, and high-level ab initio quantum chemical calculations. This marks the discovery of the final valence triplet state of C2spectroscopically accessible from the lowest triplet state. It is found to be vibronically coupled to the recently discovered 43Πgstate, necessitating vibronic calculations beyond the Born-Oppenheimer approximation to reconcile calculated rotational constants with observations. The 33Πgstate of C2is observed to have a much shorter fluorescence lifetime than expected, possibly pointing to predissociation by coupling to the unbound d3Πgstate.
authors.affiliation: School of Chemistry, UNSW, Sydney, New South Wales 2052, Australia.
authors.forename: O
authors.initials: O
authors.lastname: Krechkivska
authors.affiliation: School of Chemistry, UNSW, Sydney, New South Wales 2052, Australia.
authors.forename: B A
authors.identifier: 0000000201637690
authors.initials: BA
authors.lastname: Welsh
authors.affiliation: School of Chemistry, The University of Sydney, Sydney, New South Wales 2006, Australia.
authors.forename: G B
authors.initials: GB
authors.lastname: Bacskay
authors.affiliation: School of Chemistry, UNSW, Sydney, New South Wales 2052, Australia.
authors.forename: K
authors.initials: K
authors.lastname: Nauta
authors.affiliation: School of Chemistry, UNSW, Sydney, New South Wales 2052, Australia.
authors.forename: S H
authors.initials: SH
authors.lastname: Kable
authors.affiliation: School of Chemistry, UNSW, Sydney, New South Wales 2052, Australia.
authors.forename: T W
authors.identifier: 0000000166911438
authors.initials: TW
authors.lastname: Schmidt