Electronic ground and excited state spectroscopy of C6H and C6D

Rotational transitions in the X(2)Pi ground state of C6H and C6D have been measured by Fourier transform microwave and millimeter-wave absorption spec troscopy. 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 consta nts using a standard effective Hamiltonian for a molecule in an isolated Zn electronic state. The molecular ground state constants are used to charact erize the rotationally resolved origin band of the (2)Pi <-- X(2)Pi: electr onic transition observed by cavity ring-down laser absorption spectroscopy in a pulsed supersonic slit-jet discharge source. From these data, spectros copic constants for the excited electronic state are determined. (C) 1999 A cademic Press.