Gas-phase electronic spectra of C18 and C22 rings -: art. no. 034305

The electronic spectra of C-18 and C-22 in the 15 150-36 900 cm(-1) range have been detected in the gas phase by a mass-selective resonant two-color two-photon ionization technique coupled to a laser ablation source. The spectra were assigned to several electronic systems of monocyclic cumulenic isomers with a D-9h symmetry for C-18 and D-11h for C-22, based on time-dependent-density-functional calculations and reactivity with respect to H-2. The best cooling conditions were achieved with Kr as the buffer gas, and the origin of the (A) over tilde (1)A(2)''<-(X) over tilde (1)A(1)' transition of C-18 at 592.89 nm shows a pair of 1 cm(-1) broadbands spaced by 1.5 cm(-1). The next electronic transitions exhibited much broader, similar to 30 (in the visible) to 200 cm(-1) (in ultraviolet range), features. The spectrum of C-22 exhibits an absorption pattern similar to C-18, except that the narrow features to the red are missing; the oscillator strength of the (A) over tilde <-(X) over tilde transition is predicted to be low. (c) 2005 American Institute of Physics.