Electronic transitions of C6H4+ isomers: neon matrix and theoretical studies.
Three open-chain isomers of C6H4(+) and two cyclic ones were detected following mass-selective trapping in 6 K neon matrixes. The open-chain cations 5-hexene-1,3-diyne (CH2═CH-CC-CC-H)(+) and cis- (cis-HCC-CH═CH-CCH)(+) and trans-3-hexene-1,5-diyne (trans-HCC-CH═CH-CCH)(+), possess two absorption systems commencing at 609 and 373, 622 and 385, and 585 and 373 nm, respectively. They are assigned to the 1 (2)A" and 2 (2)A" ← X (2)A", 1(2)A2 and 2 (2)A2 ← X (2)B1, and 1 (2)Bg and 2 (2)B(g) ← X (2)A(u) electronic transitions of these cations. Two overlapping systems are detected at around 420 nm and tentatively assigned to the 1 (2)A" ← X (2)A" electronic transitions of propargyl cyclopropene and 2 (2)B1 ← X (2)A2 of o-benzyne cation structures. The assignment of the electronic transitions is based on theoretical vertical excitation energies calculated with CASPT2 and EOMEE-CCSDT methods for 12 isomers of C6H4(+). These have been carried out at the geometries optimized using several ab initio methods. Adiabatic excitation energies were calculated for the five identified isomers of C6H4(+).
Department of Chemistry, University of Basel , Klingelbergstrasse 80, CH-4056 Basel, Switzerland.
Jan
J
Fulara
Adam
A
Nagy
Karol
K
Filipkowski
Venkatesan S
VS
Thimmakondu
John F
JF
Stanton
John P
JP
Maier