Electronic absorption spectrum of a nonlinear carbon chain: trans-C6H4+.

The 2Bg-X2Au transition of a nonlinear carbon chain trans-C6H4+, and trans-C6D4+, has been observed in the gas phase. The spectra were detected in the 580 nm region by direct absorption with a cavity ringdown technique through a supersonic planar discharge. Though the rotational structure is not resolved, the band profiles were analyzed using a "total spectral fitting" procedure using ground-state constants calculated by the CASSCF and CASPT2 methods.

Electronic Ground and Excited State Spectroscopy of C(6)H and C(6)D.

Rotational transitions in the X(2)Pi ground state of C(6)H and C(6)D have been measured by Fourier transform microwave and millimeter-wave absorption spectroscopy. More than 150 rotational lines in the ground (2)Pi(3/2) and (2)Pi(1/2) ladders have been observed, allowing an accurate determination of the rotational, fine structure, lambda-doubling, and hyperfine coupling constants using a standard effective Hamiltonian for a molecule in an isolated (2)Pi electronic state. The molecular ground state constants are used to characterize the rotationally resolved origin band of the (2)Pi <-- X(2)Pi electronic transition observed by cavity ring-down laser absorption spectroscopy in a pulsed supersonic slit-jet discharge source.