New (A)over-tilde-(X)over-tilde vibronic bands of laser-vaporized C3

The laser-induced fluorescence (LIF) spectrum for the (A)over-tilde(1)pi(u)-(X)over-tilde (1)sigma(g)(+) band of C-3 was observed under jet-cooled conditions. On the basis of our previous report [Chem. Phys. Lett. 242, 435 (1995)], in which the nu(3) fundamental in the (A)over-tilde(1)pi(u) state was determined to be 541.7(1) cm(-1) through the first identification of the (A)over-tilde(0,0,1)-(X)-over-tilde(0,0,1) hot-band transition, we extended the measurements of the nu(3) related key bands; the high-resolution spectra (delta nu similar-to 0.08 cm(-1)) of eight vibronically allowed sigma(u)(+)-sigma(g)(+)-type transitions and two pi(g)-Sigma(u)(+) hot-band transitions were measured, and their rotational structures were analyzed. The determined band-origin wave numbers and the symmetries of the rotational structures led to firm assignments of the vibrational levels in the (A)over-tilde(1)pi(u) state. Using the vibrational level energies of the (A)over-tilde(0,0,nu(3)) (nu(3)=1-3) levels, the anharmonic potential along the nu(3) mode in the (A)over-tilde(1)pi(u) state was estimated to have double minima with a barrier height of 284.3 cm(-1) at the linear configuration. (C) 1998 American Institute of Physics.