title: Electronic transitions of C₅H₃⁺ and C₅H₃: neon matrix and CASPT2 studies.
abstract: Two absorption systems of C5H3(+) starting at 350 and 345 nm were detected following mass-selective deposition of m/e = 63 ions in a 6 K neon matrix. These are assigned to the 1 (1)A1 ← X (1)A1 electronic transition of 1,2,3,4-pentatetraenylium H2CCCCCH(+) (isomer B(+)) and 1 (1)B2 ← X (1)A1 of penta-1,4-diyne-3-ylium HCCCHCCH(+) (C(+)). The absorptions of neutral C5H3 isomers with onsets at 434.5, 398.3, 369.0, and 267.3 nm are also detected. The first two systems are assigned to the 1 (2)B1 ← X (2)B1 and 1 (2)A2 ← X (2)B1 transitions of isomer B and C, respectively, and the latter two to ethynylcyclopropenyl (A) and 3-vinylidenecycloprop-1-enyl (D) radicals. The structural assignments are based on the adiabatic excitation energies calculated with the MS-CASPT2 method. A vibrational analysis of the electronic spectra, based on the calculated harmonic frequencies, supports this.
authors.affiliation: Department of Chemistry, University of Basel, Klingelbergstrasse 80, CH-4056 Basel, Switzerland.
authors.forename: Jan
authors.initials: J
authors.lastname: Fulara
authors.affiliation: Department of Chemistry, University of Basel, Klingelbergstrasse 80, CH-4056 Basel, Switzerland.
authors.forename: Arghya
authors.initials: A
authors.lastname: Chakraborty
authors.affiliation: Department of Chemistry, University of Basel, Klingelbergstrasse 80, CH-4056 Basel, Switzerland.
authors.forename: Adam
authors.initials: A
authors.lastname: Nagy
authors.affiliation: Department of Chemistry, University of Basel, Klingelbergstrasse 80, CH-4056 Basel, Switzerland.
authors.forename: Karol
authors.initials: K
authors.lastname: Filipkowski
authors.affiliation: Department of Chemistry, University of Basel, Klingelbergstrasse 80, CH-4056 Basel, Switzerland.
authors.forename: John P
authors.initials: JP
authors.lastname: Maier