Interaction of T 1 and S 1 States of h 4 ‐ and d 4 ‐Acetaldehyde Using a Quantum‐Beat Technique

Decays of fluorescence of h 4 ‐ and d 4 ‐acetaldehyde are measured. The quantum‐beat structure is observed for both isotopic species. This oscillatory phenomenon is due to interaction of the state S 1 (Ã′ A″) and T 1 . Below the dissociation threshold to form products methyl and formyl radicals, an upper limit of a lifetime is set at 195‐800 ns for perturbed triplet states of CD 3 CDO; the lifetime is calculated directly from the linewidth of Fourier‐transformed spectra. At excitation wavelength shorter than 316.12 nm, the transformed linewidth increases, indicating the onset of CD 3 + DCO formation.