15min:

J. LIU AND T. A. MILLER, Department of Chemistry, The Ohio State University, 120 W. 18th Avenue, Columbus, OH 43210, USA.

The - laser-induced-fluorescence (LIF) spectrum of jet-cooled iso-propoxy radical (i-C₃H₇O ) has been recorded. The observed rotational and fine structure of the origin band has been well simulated with rotational constants for both the and states and the electron spin-rotation constants of the state. The line intensities are well simulated with a parallel transition type, requiring the same symmetry for the as for the state (A '), which confirms the previous suggestion that going from ethoxy (C₂H₅O ) to iso-propoxy, the energy ordering of the in- and the out-of-plane half-filled p-orbitals is reversed and the ground state symmetry changes from A'' to A'. The fit rotational constants are consistent with those obtained from the quantum chemistry calculations. However, the fit spin-rotation constants, particularly the nonzero _aa with a-axis perpendicular to the C_s plane, can not be explained by second-order perturbation theory. Nevertheless they can be semi-quantitatively explained based on the transferability of the electron spin-molecular rotation tensor in the axis system defined by the half-filled p-orbital and the p -orbital using ethoxy as the reference molecule. The failure of the second-order perturbation theory, as well as that of the pure precession approximation, is due to the strong vibronic interaction between the near-degenerate and states. The vibrationless levels of these two states are separated by only 68 cm^-1 as determined in previous disperse-fluorescence study. The near degeneracy of the and states of iso-propoxy and reversal of the energy ordering going from ethoxy to iso-propoxy have also been demonstrated in quantum chemistry calculations. Based on the result of iso-propoxy, spin-rotation constants of other secondary alkoxy radicals can be predicted and used for the simulation of the - rovibronic spectra of these radicals. Specifically, analysis of the high-resolution LIF spectrum of cyclohexoxy (c-C₆H₁₁O ) is ongoing.