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

[[abstract]]We studied the state-resolved dynamics of acetaldehyde in electronically excited state (A) over tildeA " with high resolution, 0.025 cm(-1). Near a threshold for dissociation into CH3 + HCO that is 1500-1750 cm(-1) above the vibrational ground state of acetaldehyde in (A) over barA ", the vibrational levels are investigated with laser-induced fluorescence. The rotational structures of four bands in this region are partially assigned. These assignments allow us to determine the dependence of relaxation of individual rovibrational levels on energy as well as rotational quantum number J. The measured lifetimes vary with J as a result of an increased number of nuclear hyperfine T-1 states that couple with a selected vibrationally excited state. For these four vibrational levels the rate constants of fragment HCO appearance are greater than decay for initially prepared excited states; this deviation implies that only a fraction of initially prepared states couple effectively to dissociation.[[fileno]]2010306010035[[department]]化學