Cl. Huang et al., State-resolved dissociation dynamics of triplet acetaldehyde near the dissociation threshold to form CH3+HCO, J CHEM PHYS, 112(4), 2000, pp. 1797-1803
We studied the state-resolved dynamics of S-1 acetaldehyde to product chann
els with quantum-beat spectroscopy. Two bands near the threshold of dissoci
ation to radical products CH3 + HCO in a supersonic jet, displaying most qu
antum-beat features, are recorded with resolution 0.025 cm(-1). Evaluated o
n the basis of a simple asymmetric rotor, the origins of these two bands 14
(0)(2-)15(0)(1) and another denoted # are 31 275.045(1) and 31 523.263(1) c
m(-1); effective rotational constants of excited state are A = 5.7883(1), 5
.0408(3), B = 0.33269(2), 0.32320(2) and C = 0.31026(2), 0.32091(2) cm(-1),
respectively; large A value results from lack of consideration of torsiona
l motion. For these two vibrational levels most rotational states (about 70
percent) display quantum-beat features attributed to coherently excited si
nglet-triplet eigenstates. The linewidth in transformed spectra for level #
, similar to 125 cm(-1) below the dissociation threshold, increases with in
creasing total angular momentum J whereas level 14(2-)15(1) that is 375 cm(
-1) below shows a small linewidth independent of J. This is because correla
tion of the triplet state with dissociation to form radical products result
s in a decreased lifetime of the triplet state in the tunneling region. A s
ystematic dependence on rotational quantum number implies Coriolis-induced
vibrational coupling of triplet states to dissociating continuum on the exi
t side of the dissociation barrier. (C) 2000 American Institute of Physics.
[S0021-9606(00)00704-2].