State-resolved dynamics of dissociation of triplet acetaldehyde: Rate of appearance of fragment HCO and decay of excited states of parent molecule

We studied the state-resolved dynamics of acetaldehyde in electronically ex cited state (A) over tildeA " with high resolution, 0.025 cm(-1). Near a th reshold for dissociation into CH3 + HCO that is 1500-1750 cm(-1) above the vibrational ground state of acetaldehyde in (A) over barA ", the vibrationa l levels are investigated with laser-induced fluorescence. The rotational s tructures of four bands in this region are partially assigned. These assign ments allow us to determine the dependence of relaxation of individual rovi brational levels on energy as well as rotational quantum number J. The meas ured lifetimes vary with J as a result of an increased number of nuclear hy perfine T-1 states that couple with a selected vibrationally excited state. For these four vibrational levels the rate constants of fragment HCO appea rance are greater than decay for initially prepared excited states; this de viation implies that only a fraction of initially prepared states couple ef fectively to dissociation.