Effect of methyl rotation on the electronic spectrum of the methyl peroxy radical

Recent experiments have prompted a theoretical investigation of the effect of methyl rotation on the A-X electronic spectrum of the CH3O2 and CD3O2 radicals. Quantum chemistry calculations have mapped the potential for the methyl rotation. Using these results, we calculate the torsional eigenvalues for both the A and X states and simulate the A-X spectrum. We find that the simulation captures the salient features of the spectrum. These features include torsional sequence structure, whose band contours change dramatically as the lower level nears the barrier, as well as atypical torsional transitions occurring from levels near the top and above the barrier. Experimental barrier heights are deduced for both the X and A states of methyl peroxy by modestly scaling the calculated potential to best reproduce the observed spectra. (C) 2007 American Institute of Physics.